New materials and structures for photovoltaics

NASA Astrophysics Data System (ADS)

Zunger, Alex; Wagner, S.; Petroff, P. M.

1993-01-01

Despite the fact that over the years crystal chemists have discovered numerous semiconducting substances, and that modern epitaxial growth techniques are able to produce many novel atomic-scale architectures, current electronic and opto-electronic technologies are based but on a handful of ˜10 traditional semiconductor core materials. This paper surveys a number of yet-unexploited classes of semiconductors, pointing to the much-needed research in screening, growing, and characterizing promising members of these classes. In light of the unmanageably large number of a-priori possibilities, we emphasize the role that structural chemistry and modern computer-aided design must play in screening potentially important candidates. The basic classes of materials discussed here include nontraditional alloys, such as non-isovalent and heterostructural semiconductors, materials at reduced dimensionality, including superlattices, zeolite-caged nanostructures and organic semiconductors, spontaneously ordered alloys, interstitial semiconductors, filled tetrahedral structures, ordered vacancy compounds, and compounds based on d and f electron elements. A collaborative effort among material predictor, material grower, and material characterizer holds the promise for a successful identification of new and exciting systems.

Low-power nanophotonics: material and device technology

NASA Astrophysics Data System (ADS)

Thylén, Lars; Holmstrom, Petter; Wosinski, Lech; Lourdudoss, Sebastian

2013-05-01

Development in photonics for communications and interconnects pose increasing requirements on reduction of footprint, power dissipation and cost, as well as increased bandwidth. Nanophotonics integrated photonics has been viewed as a solution to this, capitalizing on development in nanotechnology and an increased understanding of light matter interaction on the nanoscale. The latter can be exemplified by plasmonics and low dimensional semiconductors such as quantum dots (QDs). In this scenario the development of improved electrooptic materials is of great importance, the electrooptic polymers being an example, since they potentially offer superior properties for optical phase modulators in terms of power and integratability. Phase modulators are essential for e.g. the rapidly developing advanced modulation formats, since phase modulation basically can generate any type of modulation. The electrooptic polymers, in combination with plasmonics nanoparticle array waveguides or nanostructured hybrid plasmonic media can give extremely compact and low power dissipation modulators. Low-dimensional semiconductors, e.g. in the shape of QDs, can be employed for modulation or switching functions, offering possibilities for scaling to 2 or 3 dimensions for advanced switching functions. In both the high field confinement plasmonics and QDs, the nanosizing is due to nearfield interactions, albeit being of different physical origin in the two cases. Epitaxial integration of III-V structures on Si plays an important role in developing high-performance light sources on silicon, eventually integrated with silicon electronics. A brief remark on all-optical vs. electronically controlled optical switching systems is also given.

Electrically pumped edge-emitting photonic bandgap semiconductor laser

DOEpatents

Lin, Shawn-Yu; Zubrzycki, Walter J.

2004-01-06

A highly efficient, electrically pumped edge-emitting semiconductor laser based on a one- or two-dimensional photonic bandgap (PBG) structure is described. The laser optical cavity is formed using a pair of PBG mirrors operating in the photonic band gap regime. Transverse confinement is achieved by surrounding an active semiconductor layer of high refractive index with lower-index cladding layers. The cladding layers can be electrically insulating in the passive PBG mirror and waveguide regions with a small conducting aperture for efficient channeling of the injection pump current into the active region. The active layer can comprise a quantum well structure. The quantum well structure can be relaxed in the passive regions to provide efficient extraction of laser light from the active region.

The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdul-Jabbar, N. M.; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Kalkan, B.

2014-08-04

We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10–11 GPa in contrast to those with aperiodic structures, which amorphize around 7–8 GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga{sub 2}SeTe{sub 2} provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This ismore » corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.« less

Flexible metal-semiconductor-metal device prototype on wafer-scale thick boron nitride layers grown by MOVPE.

PubMed

Li, Xin; Jordan, Matthew B; Ayari, Taha; Sundaram, Suresh; El Gmili, Youssef; Alam, Saiful; Alam, Muhbub; Patriarche, Gilles; Voss, Paul L; Paul Salvestrini, Jean; Ougazzaden, Abdallah

2017-04-11

Practical boron nitride (BN) detector applications will require uniform materials over large surface area and thick BN layers. To report important progress toward these technological requirements, 1~2.5 µm-thick BN layers were grown on 2-inch sapphire substrates by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties were carefully characterized and discussed. The thick layers exhibited strong band-edge absorption near 215 nm. A highly oriented two-dimensional h-BN structure was formed at the film/sapphire interface, which permitted an effective exfoliation of the thick BN film onto other adhesive supports. And this structure resulted in a metal-semiconductor-metal (MSM) device prototype fabricated on BN membrane delaminating from the substrate. MSM photodiode prototype showed low dark current of 2 nA under 100 V, and 100 ± 20% photoconductivity yield for deep UV light illumination. These wafer-scale MOVPE-grown thick BN layers present great potential for the development of deep UV photodetection applications, and even for flexible (opto-) electronics in the future.

Mesoscopic Free Path of Nonthermalized Photogenerated Carriers in a Ferroelectric Insulator.

PubMed

Gu, Zongquan; Imbrenda, Dominic; Bennett-Jackson, Andrew L; Falmbigl, Matthias; Podpirka, Adrian; Parker, Thomas C; Shreiber, Daniel; Ivill, Mathew P; Fridkin, Vladimir M; Spanier, Jonathan E

2017-03-03

We show how finite-size scaling of a bulk photovoltaic effect-generated electric field in epitaxial ferroelectric insulating BaTiO_{3}(001) films and a photo-Hall response involving the bulk photovoltaic current reveal a large room-temperature mean free path of photogenerated nonthermalized electrons. Experimental determination of mesoscopic ballistic optically generated carrier transport opens a new paradigm for hot electron-based solar energy conversion, and for facile control of ballistic transport distinct from existing low-dimensional semiconductor interfaces, surfaces, layers, or other structures.

Study of low dimensional SiGe island on Si for potential visible Metal-Semiconductor-Metal photodetector

NASA Astrophysics Data System (ADS)

Rahim, Alhan Farhanah Abd; Zainal Badri, Nur'Amirah; Radzali, Rosfariza; Mahmood, Ainorkhilah

2017-11-01

In this paper, an investigation of design and simulation of silicon germanium (SiGe) islands on silicon (Si) was presented for potential visible metal semiconductor metal (MSM) photodetector. The characterization of the performances in term of the structural, optical and electrical properties of the structures was analyzed from the simulation results. The project involves simulation using SILVACO Technology Computer Aided Design (TCAD) tools. The different structures of the silicon germanium (SiGe) island on silicon substrate were created, which were large SiGe, small SiGe, combination SiGe and bulk Ge. All the structures were tested for potential Metal Semiconductor Metal (MSM) photodetector. The extracted data such as current versus voltage characteristic, current gain and spectral response were obtained using ATLAS SILVACO tools. The performance of SiGe island structures and bulk Ge on Si substrate as (MSM) photodetector was evaluated by photo and dark current-voltage (I-V) characteristics. It was found that SiGe islands exhibited higher energy band gap compared to bulk Ge. The SiGe islands current-voltage characteristics showed improved current gain compared to bulk Ge. Specifically the enhancement of the islands gain was contributed by the enhanced photo currents and lower dark currents. The spectral responses of the SiGe islands showed peak response at 590 nm (yellow) which is at the visible wavelength. This shows the feasibility of the SiGe islands to be utilized for visible photodetections.

On the current drive capability of low dimensional semiconductors: 1D versus 2D

DOE PAGES

Zhu, Y.; Appenzeller, J.

2015-10-29

Low-dimensional electronic systems are at the heart of many scaling approaches currently pursuit for electronic applications. Here, we present a comparative study between an array of one-dimensional (1D) channels and its two-dimensional (2D) counterpart in terms of current drive capability. Lastly, our findings from analytical expressions derived in this article reveal that under certain conditions an array of 1D channels can outperform a 2D field-effect transistor because of the added degree of freedom to adjust the threshold voltage in an array of 1D devices.

Confinement and Diffusion Effects in Dynamical Nuclear Polarization in Low Dimensional Nanostructures

NASA Astrophysics Data System (ADS)

Henriksen, Dan; Tifrea, Ionel

2012-02-01

We investigate the dynamic nuclear polarization as it results from the hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. The natural confinement provided by low dimensional nanostructures is responsible for an efficient nuclear spin - electron spin hyperfine coupling [1] and for a reduced value of the nuclear spin diffusion constant [2]. In the case of optical pumping, the induced nuclear spin polarization is position dependent even in the presence of nuclear spin diffusion. This effect should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for the case of GaAs quantum well structures.[4pt] [1] I. Tifrea and M. E. Flatt'e, Phys. Rev. B 84, 155319 (2011).[0pt] [2] A. Malinowski and R. T. Harley, Solid State Commun. 114, 419 (2000).

α,ω-dihexyl-sexithiophene thin films for solution-gated organic field-effect transistors

NASA Astrophysics Data System (ADS)

Schamoni, Hannah; Noever, Simon; Nickel, Bert; Stutzmann, Martin; Garrido, Jose A.

2016-02-01

While organic semiconductors are being widely investigated for chemical and biochemical sensing applications, major drawbacks such as the poor device stability and low charge carrier mobility in aqueous electrolytes have not yet been solved to complete satisfaction. In this work, solution-gated organic field-effect transistors (SGOFETs) based on the molecule α,ω-dihexyl-sexithiophene (DH6T) are presented as promising platforms for in-electrolyte sensing. Thin films of DH6T were investigated with regard to the influence of the substrate temperature during deposition on the grain size and structural order. The performance of SGOFETs can be improved by choosing suitable growth parameters that lead to a two-dimensional film morphology and a high degree of structural order. Furthermore, the capability of the SGOFETs to detect changes in the pH or ionic strength of the gate electrolyte is demonstrated and simulated. Finally, excellent transistor stability is confirmed by continuously operating the device over a period of several days, which is a consequence of the low threshold voltage of DH6T-based SGOFETs. Altogether, our results demonstrate the feasibility of high performance and highly stable organic semiconductor devices for chemical or biochemical applications.

Effects of sudden density changes in disordered superconductors and semiconductors

NASA Astrophysics Data System (ADS)

Assi, Hiba; Chaturvedi, Harshwardhan; Pleimling, Michel; Täuber, Uwe

Vortices in type-II superconductors in the presence of extended, linear defects display the strongly pinned Bose glass phase at low temperatures. This disorder-dominated thermodynamic state is characterized by suppressed lateral flux line fluctuations and very slow structural relaxation kinetics: The vortices migrate between different columnar pinning centers to minimize the mutual repulsive interactions and eventually optimize the system's pinning configuration. To monitor the flux lines' late-time structural relaxations, we employ a mapping between an effectively two-dimensional Bose glass system and a modified Coulomb glass model, originally developed to describe disordered semiconductors at low temperatures. By means of Monte Carlo simulations, we investigate the effects of the introduction of random bare site energies and sudden changes in the vortex or charge carrier density on the soft Coulomb gap that appears in the density of states due to the emerging spatial anticorrelations. The non-equilibrium relaxation properties of the Bose and Coulomb glass states and the ensuing aging kinetics are studied through the two-time density autocorrelation function and its various scaling forms. Research supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-09ER46613.

Quantized conductance doubling and hard gap in a two-dimensional semiconductor-superconductor heterostructure.

PubMed

Kjaergaard, M; Nichele, F; Suominen, H J; Nowak, M P; Wimmer, M; Akhmerov, A R; Folk, J A; Flensberg, K; Shabani, J; Palmstrøm, C J; Marcus, C M

2016-09-29

Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards topological matter is by coupling a 2D electron gas with strong spin-orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e 2 /h, consistent with theory. The hard-gap semiconductor-superconductor system demonstrated here is amenable to top-down processing and provides a new avenue towards low-dissipation electronics and topological quantum systems.

Spectroscopic characterization of III-V semiconductor nanomaterials

NASA Astrophysics Data System (ADS)

Crankshaw, Shanna Marie

III-V semiconductor materials form a broad basis for optoelectronic applications, including the broad basis of the telecom industry as well as smaller markets for high-mobility transistors. In a somewhat analogous manner as the traditional silicon logic industry has so heavily depended upon process manufacturing development, optoelectronics often relies instead on materials innovations. This thesis focuses particularly on III-V semiconductor nanomaterials, detailed characterization of which is invaluable for translating the exhibited behavior into useful applications. Specifically, the original research described in these thesis chapters is an investigation of semiconductors at a fundamental materials level, because the nanostructures in which they appear crystallize in quite atypical forms for the given semiconductors. Rather than restricting the experimental approaches to any one particular technique, many different types of optical spectroscopies are developed and applied where relevant to elucidate the connection between the crystalline structure and exhibited properties. In the first chapters, for example, a wurtzite crystalline form of the prototypical zincblende III-V binary semiconductor, GaAs, is explored through polarization-dependent Raman spectroscopy and temperature-dependent photoluminescence, as well as second-harmonic generation (SHG). The altered symmetry properties of the wurtzite crystalline structure are particularly evident in the Raman and SHG polarization dependences, all within a bulk material realm. A rather different but deeply elegant aspect of crystalline symmetry in GaAs is explored in a separate study on zincblende GaAs samples quantum-confined in one direction, i.e. quantum well structures, whose quantization direction corresponds to the (110) direction. The (110) orientation modifies the low-temperature electron spin relaxation mechanisms available compared to the usual (001) samples, leading to altered spin coherence times explored through a novel spectroscopic technique first formulated for the rather different purpose of dispersion engineering for slow-light schemes. The frequency-resolved technique combined with the unusual (110) quantum wells in a furthermore atypical waveguide experimental geometry has revealed fascinating behavior of electron spin splitting which points to the possibility of optically orienting electron spins with linearly polarized light---an experimental result supporting a theoretical description of the phenomenon itself only a few years old. Lastly, to explore a space of further-restricted dimensionality, the final chapters describe InP semiconductor nanowires with dimensions small enough to be considered truly one-dimensional. Like the bulk GaAs of the first few chapters, the InP nanowires here crystallize in a wurtzite structure. In the InP nanowire case, though, the experimental techniques explored for characterization are temperature-dependent time-integrated photoluminescence at the single-wire level (including samples with InAsP insertions) and time-resolved photoluminescence at the ensemble level. The carrier dynamics revealed through these time-resolved studies are the first of their kind for wurtzite InP nanowires. The chapters are thus ordered as a progression from three (bulk), to two (quantum well), to one (nanowire), to zero dimensions (axially-structured nanowire), with the uniting theme the emphasis on connecting the semiconductor nanomaterials' crystallinity to its exhibited properties by relevant experimental spectroscopic techniques, whether these are standard methods or effectively invented for the case at hand.

An Assessment of Critical Dimension Small Angle X-ray Scattering Metrology for Advanced Semiconductor Manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Settens, Charles M.

2015-01-01

Simultaneous migration of planar transistors to FinFET architectures, the introduction of a plurality of materials to ensure suitable electrical characteristics, and the establishment of reliable multiple patterning lithography schemes to pattern sub-10 nm feature sizes imposes formidable challenges to current in-line dimensional metrologies. Because the shape of a FinFET channel cross-section immediately influences the electrical characteristics, the evaluation of 3D device structures requires measurement of parameters beyond traditional critical dimension (CD), including their sidewall angles, top corner rounding and footing, roughness, recesses and undercuts at single nanometer dimensions; thus, metrologies require sub-nm and approaching atomic level measurement uncertainty. Synchrotron criticalmore » dimension small angle X-ray scattering (CD-SAXS) has unique capabilities to non-destructively monitor the cross-section shape of surface structures with single nanometer uncertainty and can perform overlay metrology to sub-nm uncertainty. In this dissertation, we perform a systematic experimental investigation using CD-SAXS metrology on a hierarchy of semiconductor 3D device architectures including, high-aspect-ratio contact holes, H2 annealed Si fins, and a series of grating type samples at multiple points along a FinFET fabrication process increasing in structural intricacy and ending with fully fabricated FinFET. Comparative studies between CD-SAXS metrology and other relevant semiconductor dimensional metrologies, particularly CDSEM, CD-AFM and TEM are used to determine physical limits of CD-SAXS approach for advanced semiconductor samples. CD-SAXS experimental tradeoffs, advice for model-dependent analysis and thoughts on the compatibility with a semiconductor manufacturing environment are discussed.« less

Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films.

PubMed

Zhang, Yi; Ugeda, Miguel M; Jin, Chenhao; Shi, Su-Fei; Bradley, Aaron J; Martín-Recio, Ana; Ryu, Hyejin; Kim, Jonghwan; Tang, Shujie; Kim, Yeongkwan; Zhou, Bo; Hwang, Choongyu; Chen, Yulin; Wang, Feng; Crommie, Michael F; Hussain, Zahid; Shen, Zhi-Xun; Mo, Sung-Kwan

2016-04-13

High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.

Electronic structure, surface doping, and optical response in epitaxial WSe 2 thin films

DOE PAGES

Zhang, Yi; Ugeda, Miguel M.; Jin, Chenhao; ...

2016-03-14

High quality WSe 2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe 2/BLG. We observe that a bilayer of WSe 2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct–indirect band gap crossover to trilayer WSe 2. In the monolayer limit, WSe 2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observedmore » among all the MX 2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe 2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Lastly, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.« less

Using surfaces, ligands, and dimensionality to obtain desired nanostructure properties

NASA Astrophysics Data System (ADS)

Nagpal, Prashant; Singh, Vivek; Ding, Yuchen

2014-03-01

Nanostructured materials are intensively investigated to obtain material properties different from their bulk counterparts. It has been demonstrated that nanoscaled semiconductor can have interesting size, shape and morphology dependent optoelectronic properties. But the effect of surfaces, ligands and dimensionality (0D quantum dots to 2D nanosheets) has been largely unexplored. Here, we will show how tuning the surface and dimensionality can affect the electronic states of the semiconductor, and how these states can play an important role in their fundamental photophysical properties or thermal transport. Using the specific case for silicon, we will show how ``new'' surface states in small uniform can lead to light absorption/emission without phonon assistance, while hindering the phonon-drag of charge carriers leading to low Seebeck coefficient for thermoelectric applications. These measurements will shed light on designing appropriate surface, size, and dimensionality for desired applications of nanostructured films.

Structural defects in cubic semiconductors characterized by aberration-corrected scanning transmission electron microscopy.

PubMed

Arroyo Rojas Dasilva, Yadira; Kozak, Roksolana; Erni, Rolf; Rossell, Marta D

2017-05-01

The development of new electro-optical devices and the realization of novel types of transistors require a profound understanding of the structural characteristics of new semiconductor heterostructures. This article provides a concise review about structural defects which occur in semiconductor heterostructures on the basis of micro-patterned Si substrates. In particular, one- and two-dimensional crystal defects are being discussed which are due to the plastic relaxation of epitaxial strain caused by the misfit of crystal lattices. Besides a few selected examples from literature, we treat in particular crystal defects occurring in GaAs/Si, Ge/Si and β-SiC/Si structures which are studied by high-resolution annular dark-field scanning transmission electron microscopy. The relevance of this article is twofold; firstly, it should provide a collection of data which are of help for the identification and characterization of defects in cubic semiconductors by means of atomic-resolution imaging, and secondly, the experimental data shall provide a basis for advancing the understanding of device characteristics with the aid of theoretical modelling by considering the defective nature of strained semiconductor heterostructures. Copyright © 2016 Elsevier B.V. All rights reserved.

Enhanced Exciton and Photon Confinement in Ruddlesden-Popper Perovskite Microplatelets for Highly Stable Low-Threshold Polarized Lasing.

PubMed

Li, Mingjie; Wei, Qi; Muduli, Subas Kumar; Yantara, Natalia; Xu, Qiang; Mathews, Nripan; Mhaisalkar, Subodh G; Xing, Guichuan; Sum, Tze Chien

2018-06-01

At the heart of electrically driven semiconductors lasers lies their gain medium that typically comprises epitaxially grown double heterostuctures or multiple quantum wells. The simultaneous spatial confinement of charge carriers and photons afforded by the smaller bandgaps and higher refractive index of the active layers as compared to the cladding layers in these structures is essential for the optical-gain enhancement favorable for device operation. Emulating these inorganic gain media, superb properties of highly stable low-threshold (as low as ≈8 µJ cm -2 ) linearly polarized lasing from solution-processed Ruddlesden-Popper (RP) perovskite microplatelets are realized. Detailed investigations using microarea transient spectroscopies together with finite-difference time-domain simulations validate that the mixed lower-dimensional RP perovskites (functioning as cladding layers) within the microplatelets provide both enhanced exciton and photon confinement for the higher-dimensional RP perovskites (functioning as the active gain media). Furthermore, structure-lasing-threshold relationship (i.e., correlating the content of lower-dimensional RP perovskites in a single microplatelet) vital for design and performance optimization is established. Dual-wavelength lasing from these quasi-2D RP perovskite microplatelets can also be achieved. These unique properties distinguish RP perovskite microplatelets as a new family of self-assembled multilayer planar waveguide gain media favorable for developing efficient lasers. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High Efficiency Thermoelectric Materials and Devices

NASA Technical Reports Server (NTRS)

Kochergin, Vladimir (Inventor)

2013-01-01

Growth of thermoelectric materials in the form of quantum well super-lattices on three-dimensionally structured substrates provide the means to achieve high conversion efficiency of the thermoelectric module combined with inexpensiveness of fabrication and compatibility with large scale production. Thermoelectric devices utilizing thermoelectric materials in the form of quantum well semiconductor super-lattices grown on three-dimensionally structured substrates provide improved thermoelectric characteristics that can be used for power generation, cooling and other applications..

Method for determining the composition and orientation of III-V {001} semiconductor surfaces

NASA Astrophysics Data System (ADS)

Sung, M. M.; Kim, C.; Rabalais, J. W.

1996-09-01

A method for determining the composition and orientation of III-V {001} semiconductor surfaces is presented and applications are described. The information is obtained from the techniques of time-of-flight scattering and recoiling spectrometry (TOF-SARS), using the composition from azimuth-specific elemental accessibilities (CASEA) method, and low energy electron diffraction (LEED). The azimuth-specific elemental accessibilities (ASEA) are measured experimentally and calculated from the number of accessible atoms in the unit cell and from three-dimensional trajectory simulations using the SARIC program. The in situ analyses identify the 1st-layer elemental species and determine the orientation of the reconstructed surface symmetry elements with respect to the bulk crystallographic directions. This is demonstrated for the III-V {001} compound semiconductor surfaces of GaAs and InAs in the (4 × 2) and (4 × 2) phases and InP in the (4 × 2) phase. The analyses confirm the missing-row-dimer (MRD) structure for GaAs and InAs in which the missing row direction is parallel to the direction of the 1st-layer multimers (dimers) and the missing-row-trimer-dimer (MRTD) structure for InP in which the missing row direction is perpendicular to the direction of the 1st-layer multimers (trimers).

New two-dimensional V-V binary compounds with a honeycomb-like structure: a first-principles study

NASA Astrophysics Data System (ADS)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Wang, Ling-Ling

2018-03-01

We systematically search for the stable structures of two-dimensional (2D) V-V binary compounds with honeycomb-like structure by using the first-principles calculation. We identify 26 stable structures out of 54 2D V-V compounds based on various assessments of stabilities: total energy, thermodynamics, and mechanics. Among them, 12 2D V-V compounds are previously unrecognized structures. For each class V-V isomer, the most stable structures are found to be β-AsP, β-SbAs, α-BiAs, α-BiSb, α 2-SbP, and α 2-BiP. For all isomers of the AsP, they are always stable, and hence PAs monolayer is most likely to be prepared experimentally. All the stable structures are semiconductors with bandgaps ranging from 0.06 eV to 2.52 eV at the Heyd-Scuseria-Ernzerhof level. Therefore, they are potential materials for versatile semiconductor devices. Our findings provide a new clue to facilitate the design of 2D materials for potential applications.

Probing Carrier Transport and Structure-Property Relationship of Highly Ordered Organic Semiconductors at the Two-Dimensional Limit.

PubMed

Zhang, Yuhan; Qiao, Jingsi; Gao, Si; Hu, Fengrui; He, Daowei; Wu, Bing; Yang, Ziyi; Xu, Bingchen; Li, Yun; Shi, Yi; Ji, Wei; Wang, Peng; Wang, Xiaoyong; Xiao, Min; Xu, Hangxun; Xu, Jian-Bin; Wang, Xinran

2016-01-08

One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ∼3  nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.

Probing Carrier Transport and Structure-Property Relationship of Highly Ordered Organic Semiconductors at the Two-Dimensional Limit

NASA Astrophysics Data System (ADS)

Zhang, Yuhan; Qiao, Jingsi; Gao, Si; Hu, Fengrui; He, Daowei; Wu, Bing; Yang, Ziyi; Xu, Bingchen; Li, Yun; Shi, Yi; Ji, Wei; Wang, Peng; Wang, Xiaoyong; Xiao, Min; Xu, Hangxun; Xu, Jian-Bin; Wang, Xinran

2016-01-01

One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ˜3 nm . Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.

Large-area, laterally-grown epitaxial semiconductor layers

DOEpatents

Han, Jung; Song, Jie; Chen, Danti

2017-07-18

Structures and methods for confined lateral-guided growth of a large-area semiconductor layer on an insulating layer are described. The semiconductor layer may be formed by heteroepitaxial growth from a selective growth area in a vertically-confined, lateral-growth guiding structure. Lateral-growth guiding structures may be formed in arrays over a region of a substrate, so as to cover a majority of the substrate region with laterally-grown epitaxial semiconductor tiles. Quality regions of low-defect, stress-free GaN may be grown on silicon.

Quantum states and optical responses of low-dimensional electron hole systems

NASA Astrophysics Data System (ADS)

Ogawa, Tetsuo

2004-09-01

Quantum states and their optical responses of low-dimensional electron-hole systems in photoexcited semiconductors and/or metals are reviewed from a theoretical viewpoint, stressing the electron-hole Coulomb interaction, the excitonic effects, the Fermi-surface effects and the dimensionality. Recent progress of theoretical studies is stressed and important problems to be solved are introduced. We cover not only single-exciton problems but also few-exciton and many-exciton problems, including electron-hole plasma situations. Dimensionality of the Wannier exciton is clarified in terms of its linear and nonlinear responses. We also discuss a biexciton system, exciton bosonization technique, high-density degenerate electron-hole systems, gas-liquid phase separation in an excited state and the Fermi-edge singularity due to a Mahan exciton in a low-dimensional metal.

Effect of Γ-X band mixing on the donor binding energy in a Quantum Wire

NASA Astrophysics Data System (ADS)

Vijaya Shanthi, R.; Jayakumar, K.; Nithiananthi, P.

2015-02-01

To invoke the technological applications of heterostructure semiconductors like Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD), it is important to understand the property of impurity energy which is responsible for the peculiar electronic & optical behavior of the Low Dimensional Semiconductor Systems (LDSS). Application of hydrostatic pressure P>35kbar drastically alters the band offsets leading to the crossover of Γ band of the well & X band of the barrier resulting in an indirect transition of the carrier and this effect has been studied experimentally and theoretically in a QW structure. In this paper, we have investigated the effect of Γ-X band mixing due to the application of hydrostatic pressure in a GaAs/AlxGa1-xAs QWW system. The results are presented and discussed for various widths of the wire.

Copper Vacancies and Heavy Holes in the Two-Dimensional Semiconductor KCu 3–xSe 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rettie, Alexander J. E.; Sturza, Mihai; Malliakas, Christos D.

The two-dimensional material KCu 3–xSe 2 was synthesized using both a K 2Se 3 flux and directly from the elements. It crystallizes in the CsAg 3S 2 structure (monoclinic space group C2/m with a = 15.417(3) Å, b = 4.0742(8) Å, c = 8.3190(17) Å, and β = 112.94(3)°), and single-crystal refinement revealed infinite copper-deficient [Cu 3–xSe 2]– layers separated by K + ions. Thermal analysis indicated that KCu 3–xSe 2 melts congruently at ~755 °C. UV–vis spectroscopy showed an optical band gap of ~1.35 eV that is direct in nature, as confirmed by electronic structure calculations. Electronic transport measurementsmore » on single crystals yielded an in-plane resistivity of ~6 × 10 –1 Ω cm at 300 K that has a complex temperature dependence. The results of Seebeck coefficient measurements were consistent with a doped p-type semiconductor (S = +214 μV K –1 at 300 K), with doping being attributed to copper vacancies. Transport is dominated by low-mobility (on the order of 1 cm 2 V –1 s –1) holes caused by relatively flat valence bands with substantial Cu 3d character and a significant concentration of Cu ion vacancy defects (p ~ 10 19 cm –3) in this material. In conclusion, electronic band structure calculations showed that electrons should be significantly more mobile in this structure type.« less

Copper Vacancies and Heavy Holes in the Two-Dimensional Semiconductor KCu 3–xSe 2

DOE PAGES

Rettie, Alexander J. E.; Sturza, Mihai; Malliakas, Christos D.; ...

2017-06-21

The two-dimensional material KCu 3–xSe 2 was synthesized using both a K 2Se 3 flux and directly from the elements. It crystallizes in the CsAg 3S 2 structure (monoclinic space group C2/m with a = 15.417(3) Å, b = 4.0742(8) Å, c = 8.3190(17) Å, and β = 112.94(3)°), and single-crystal refinement revealed infinite copper-deficient [Cu 3–xSe 2]– layers separated by K + ions. Thermal analysis indicated that KCu 3–xSe 2 melts congruently at ~755 °C. UV–vis spectroscopy showed an optical band gap of ~1.35 eV that is direct in nature, as confirmed by electronic structure calculations. Electronic transport measurementsmore » on single crystals yielded an in-plane resistivity of ~6 × 10 –1 Ω cm at 300 K that has a complex temperature dependence. The results of Seebeck coefficient measurements were consistent with a doped p-type semiconductor (S = +214 μV K –1 at 300 K), with doping being attributed to copper vacancies. Transport is dominated by low-mobility (on the order of 1 cm 2 V –1 s –1) holes caused by relatively flat valence bands with substantial Cu 3d character and a significant concentration of Cu ion vacancy defects (p ~ 10 19 cm –3) in this material. In conclusion, electronic band structure calculations showed that electrons should be significantly more mobile in this structure type.« less

Low-dimensional materials for organic electronic applications

NASA Astrophysics Data System (ADS)

Beniwal, Sumit

This thesis explores the self-assembly, surface interactions and electronic properties of functional molecules that have potential applications in electronics. Three classes of molecules - organic ferroelectric, spin-crossover complex, and molecules that assemble into a 2D semiconductor, have been studied through scanning tunneling microscopy and surfacesensitive spectroscopic methods. The scientific goal of this thesis is to understand the self-assembly of these molecules in low-dimensional (2D) configurations and the influence of substrate on their properties.

Template-Assisted Hydrothermal Growth of One-Dimensional Zinc Oxide Nanowires for Photocatalytic Application.

PubMed

Ma, Shuai-Shuai; Xu, Peng; Cai, Zhi-Lan; Li, Qing; Ye, Zhao-Lian; Zhou, Yu-Ming

2018-07-01

One-dimensional (1D) semiconductor ZnO nanowires have been successfully synthesized by a novel soft-chemical hydrothermal method with allylpolyethoxy amino carboxylate (AA-APEA) at low temperature. Their structure and properties have been characterized by a series of techniques, including X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM). It was found that ZnO nanowires with diameters around 50 nm and lengths up to about several micrometers are well-distributed. The photocatalytic activity toward degradation of methylene blue (MB) aqueous solution under ultraviolet (UV) was investigated and the results showed that the ZnO nanowires exhibit a markedly higher photoactivity compared to the ZnO nanoparticles which were obtained without AA-APEA polymer assistant, and it can be ascribed to the special 1D morphology of the ZnO nanowires. In particular, the rate of degradation of the ZnO nanowires was 11 times faster than that of ZnO nanoparticles. In addition, the ZnO nanowires could be easily recycled in UV photocatalytic activity. These observations could promote new applications of photocatalyst for wastewater treatment utilizing oxide semiconductor nanostructures.

Low-threshold voltage ultraviolet light-emitting diodes based on (Al,Ga)N metal-insulator-semiconductor structures

NASA Astrophysics Data System (ADS)

Liang, Yu-Han; Towe, Elias

2017-12-01

Al-rich III-nitride-based deep-ultraviolet (UV) (275-320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal-insulator-semiconductor UV light-emitting Schottky diodes with low turn-on voltages of <3 V, which are about half those of typical (Al,Ga)N p-i-n diodes. Our devices use a thin AlN film as the insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al x Ga1- x N semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.

Microgravity

NASA Image and Video Library

2004-04-15

A semiconductor's usefulness is determined by how atoms are ordered within the crystal's underlying three-dimensional structure. While this mercury telluride and cadmium telluride alloy sample mixes completely in Earth -based laboratories, convective flows prevent them from mixing uniformly.

Nonlinear structures: Cnoidal, soliton, and periodical waves in quantum semiconductor plasma

NASA Astrophysics Data System (ADS)

Tolba, R. E.; El-Bedwehy, N. A.; Moslem, W. M.; El-Labany, S. K.; Yahia, M. E.

2016-01-01

Properties and emerging conditions of various nonlinear acoustic waves in a three dimensional quantum semiconductor plasma are explored. A plasma fluid model characterized by degenerate pressures, exchange correlation, and quantum recoil forces is established and solved. Our analysis approach is based on the reductive perturbation theory for deriving the Kadomtsev-Petviashvili equation from the fluid model and solving it by using Painlevé analysis to come up with different nonlinear solutions that describe different pulse profiles such as cnoidal, soliton, and periodical pulses. The model is then employed to recognize the possible perturbations in GaN semiconductor.

Nonlinear structures: Cnoidal, soliton, and periodical waves in quantum semiconductor plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tolba, R. E., E-mail: tolba-math@yahoo.com; El-Bedwehy, N. A., E-mail: nab-elbedwehy@yahoo.com; Moslem, W. M., E-mail: wmmoslem@hotmail.com

2016-01-15

Properties and emerging conditions of various nonlinear acoustic waves in a three dimensional quantum semiconductor plasma are explored. A plasma fluid model characterized by degenerate pressures, exchange correlation, and quantum recoil forces is established and solved. Our analysis approach is based on the reductive perturbation theory for deriving the Kadomtsev-Petviashvili equation from the fluid model and solving it by using Painlevé analysis to come up with different nonlinear solutions that describe different pulse profiles such as cnoidal, soliton, and periodical pulses. The model is then employed to recognize the possible perturbations in GaN semiconductor.

Possible High Thermoelectric Power in Semiconducting Carbon Nanotubes ˜A Case Study of Doped One-Dimensional Semiconductors˜

NASA Astrophysics Data System (ADS)

Yamamoto, Takahiro; Fukuyama, Hidetoshi

2018-02-01

We have theoretically investigated the thermoelectric properties of impurity-doped one-dimensional semiconductors, focusing on nitrogen-substituted (N-substituted) carbon nanotubes (CNTs), using the Kubo formula combined with a self-consistent t-matrix approximation. N-substituted CNTs exhibit extremely high thermoelectric power factor (PF) values originating from a characteristic of one-dimensional materials where decrease in the carrier density increase both the electrical conductivity and the Seebeck coefficient in the low-N regime. The chemical potential dependence of the PF values of semiconducting CNTs has also been studied as a field-effect transistor and it turns out that the PF values show a noticeable maximum in the vicinity of the band edges. This result demonstrates that "band-edge engineering" will be crucial for solid development of high-performance thermoelectric materials.

Single layer of MX3(M = Ti, Zr; X = S, Se, Te): a new platform for nano-electronics and optics

NASA Astrophysics Data System (ADS)

Jin, Yingdi; Li, Xingxing; Yang, Jinlong

A serial of two dimensional titanium and zirconium trichalcogenides nanosheets MX3 (M=Ti, Zr; X=S, Se, Te) are investigated based on first-principles calculations. The evaluated low cleavage energy indicates that stable two dimensional monolayers can be exfoliated from their bulk crystals in experiment. Electronic studies reveal very rich electronic properties in these monolayers, including metallic TiTe3 and ZrTe3, direct band gap semiconductor TiS3 and indirect band gap semiconductors TiSe3, ZrS3 and ZrSe3. The band gaps of all the semiconductors are between 0.57~1.90 eV, which implies their potential applications in nano-electronics. And the calculated effective masses demonstrate highly anisotropic conduction properties for all the semiconductors. Optically, TiS3 and TiSe3 monolayers exhibit good light absorption in the visible and near-infrared region respectively, indicating their potential applications in optical devices. In particular, the highly anisotropic optical absorption of TiS3 monolayer suggests it could be used in designing nano optical waveguide polarizers.

Perfect absorption of modified-molybdenum-disulfide-based Tamm plasmonic structures

NASA Astrophysics Data System (ADS)

Wang, Xiaoyu; Wang, Jicheng; Hu, Zheng-Da; Sang, Tian; Feng, Yan

2018-06-01

The two-dimensional semiconductor materials of transition metal molybdenum disulfide display various special optical properties in the interaction of matter and light. In this work, we study the strong coupling between the two-dimensional materials’ excitons and Tamm plasmon polaritons (TPPs). To enhance the interaction between light and matter, we introduce the grating modulation in the traditional Tamm structure. By adjusting the structure parameters of the grating-modified Tamm system, we achieve perfect absorption in the visible region. Our research results will pave the way for the application of ultrathin polarization optical devices.

Vertical dielectric screening of few-layer van der Waals semiconductors.

PubMed

Koo, Jahyun; Gao, Shiyuan; Lee, Hoonkyung; Yang, Li

2017-10-05

Vertical dielectric screening is a fundamental parameter of few-layer van der Waals two-dimensional (2D) semiconductors. However, unlike the widely-accepted wisdom claiming that the vertical dielectric screening is sensitive to the thickness, our first-principles calculation based on the linear response theory (within the weak field limit) reveals that this screening is independent of the thickness and, in fact, it is the same as the corresponding bulk value. This conclusion is verified in a wide range of 2D paraelectric semiconductors, covering narrow-gap ones and wide-gap ones with different crystal symmetries, providing an efficient and reliable way to calculate and predict static dielectric screening of reduced-dimensional materials. Employing this conclusion, we satisfactorily explain the tunable band gap in gated 2D semiconductors. We further propose to engineer the vertical dielectric screening by changing the interlayer distance via vertical pressure or hybrid structures. Our predicted vertical dielectric screening can substantially simplify the understanding of a wide range of measurements and it is crucial for designing 2D functional devices.

Computational models for the berry phase in semiconductor quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prabhakar, S., E-mail: rmelnik@wlu.ca; Melnik, R. V. N., E-mail: rmelnik@wlu.ca; Sebetci, A.

2014-10-06

By developing a new model and its finite element implementation, we analyze the Berry phase low-dimensional semiconductor nanostructures, focusing on quantum dots (QDs). In particular, we solve the Schrödinger equation and investigate the evolution of the spin dynamics during the adiabatic transport of the QDs in the 2D plane along circular trajectory. Based on this study, we reveal that the Berry phase is highly sensitive to the Rashba and Dresselhaus spin-orbit lengths.

Observations of cavity polaritons in one-dimensional photonic crystals containing a liquid-crystalline semiconductor based on perylene bisimide units

NASA Astrophysics Data System (ADS)

Sakata, T.; Suzuki, M.; Yamamoto, T.; Nakanishi, S.; Funahashi, M.; Tsurumachi, N.

2017-10-01

We investigated the optical transmission properties of one-dimensional photonic crystal (1D-PC) microcavity structures containing the liquid-crystalline (LC) perylene tetracarboxylic bisimide (PTCBI) derivative. We fabricated the microcavity structures for this study by two different methods and observed the cavity polaritons successfully in both samples. For one sample, since the PTCBI molecules were aligned in the cavity layer of the 1D-PC by utilizing a friction transfer method, vacuum Rabi splitting energy was strongly dependent on the polarization of the incident light produced by the peculiar optical features of the LC organic semiconductor. For the other sample, we did not utilize the friction transfer method and did not observe such polarization dependence. However, we did observe a relatively large Rabi splitting energy of 187 meV, probably due to the improvement of optical confinement effect.

Large Bandgap Shrinkage from Doping and Dielectric Interface in Semiconducting Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Comfort, Everett; Lee, Ji Ung

2016-06-01

The bandgap of a semiconductor is one of its most important electronic properties. It is often considered to be a fixed property of the semiconductor. As the dimensions of semiconductors reduce, however, many-body effects become dominant. Here, we show that doping and dielectric, two critical features of semiconductor device manufacturing, can dramatically shrink (renormalize) the bandgap. We demonstrate this in quasi-one-dimensional semiconducting carbon nanotubes. Specifically, we use a four-gated device, configured as a p-n diode, to investigate the fundamental electronic structure of individual, partially supported nanotubes of varying diameter. The four-gated construction allows us to combine both electrical and optical spectroscopic techniques to measure the bandgap over a wide doping range.

Carbon nanotube-based three-dimensional monolithic optoelectronic integrated system

NASA Astrophysics Data System (ADS)

Liu, Yang; Wang, Sheng; Liu, Huaping; Peng, Lian-Mao

2017-06-01

Single material-based monolithic optoelectronic integration with complementary metal oxide semiconductor-compatible signal processing circuits is one of the most pursued approaches in the post-Moore era to realize rapid data communication and functional diversification in a limited three-dimensional space. Here, we report an electrically driven carbon nanotube-based on-chip three-dimensional optoelectronic integrated circuit. We demonstrate that photovoltaic receivers, electrically driven transmitters and on-chip electronic circuits can all be fabricated using carbon nanotubes via a complementary metal oxide semiconductor-compatible low-temperature process, providing a seamless integration platform for realizing monolithic three-dimensional optoelectronic integrated circuits with diversified functionality such as the heterogeneous AND gates. These circuits can be vertically scaled down to sub-30 nm and operates in photovoltaic mode at room temperature. Parallel optical communication between functional layers, for example, bottom-layer digital circuits and top-layer memory, has been demonstrated by mapping data using a 2 × 2 transmitter/receiver array, which could be extended as the next generation energy-efficient signal processing paradigm.

FIESTA ROC: A new finite element analysis program for solar cell simulation

NASA Technical Reports Server (NTRS)

Clark, Ralph O.

1991-01-01

The Finite Element Semiconductor Three-dimensional Analyzer by Ralph O. Clark (FIESTA ROC) is a computational tool for investigating in detail the performance of arbitrary solar cell structures. As its name indicates, it uses the finite element technique to solve the fundamental semiconductor equations in the cell. It may be used for predicting the performance (thereby dictating the design parameters) of a proposed cell or for investigating the limiting factors in an established design.

High-efficiency photovoltaic cells

DOEpatents

Yang, H.T.; Zehr, S.W.

1982-06-21

High efficiency solar converters comprised of a two cell, non-lattice matched, monolithic stacked semiconductor configuration using optimum pairs of cells having bandgaps in the range 1.6 to 1.7 eV and 0.95 to 1.1 eV, and a method of fabrication thereof, are disclosed. The high band gap subcells are fabricated using metal organic chemical vapor deposition (MOCVD), liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE) to produce the required AlGaAs layers of optimized composition, thickness and doping to produce high performance, heteroface homojunction devices. The low bandgap subcells are similarly fabricated from AlGa(As)Sb compositions by LPE, MBE or MOCVD. These subcells are then coupled to form a monolithic structure by an appropriate bonding technique which also forms the required transparent intercell ohmic contact (IOC) between the two subcells. Improved ohmic contacts to the high bandgap semiconductor structure can be formed by vacuum evaporating to suitable metal or semiconductor materials which react during laser annealing to form a low bandgap semiconductor which provides a low contact resistance structure.

Advanced thermoelectric materials with enhanced crystal lattice structure and methods of preparation

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1998-01-01

New skutterudite phases including Ru.sub.0.5 Pd.sub.0.5 Sb.sub.3, RuSb.sub.2 Te, and FeSb.sub.2 Te, have been prepared having desirable thermoelectric properties. In addition, a novel thermoelectric device has been prepared using skutterudite phase Fe.sub.0.5 Ni.sub.0.5 Sb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using powder metallurgy techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities and good Seebeck coefficients. These materials have low thermal conductivity and relatively low electrical resistivity, and are good candidates for low temperature thermoelectric applications.

Significantly improved dielectric performances of nanocomposites via loading two-dimensional core-shell structure Bi2Te3@SiO2 nanosheets

NASA Astrophysics Data System (ADS)

Chen, Jianwen; Wang, Xiucai; Yu, Xinmei; Fan, Yun; Duan, Zhikui; Jiang, Yewen; Yang, Faquan; Zhou, Yuexia

2018-07-01

Polymer/semiconductor-insulator nanocomposites can display high dielectric constants with a relatively low dissipation factor under low electric fields, and thus seem to promising for high energy density capacitors. Here, a novel nanocomposite films is developed by loading two-dimensional (2D) core-shell structure Bi2Te3@SiO2 nanosheets in the poly (vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) polymer matrix. The 2D Bi2Te3 nanosheets were prepared through simple microwave-assisted method. The experimental results suggesting that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the dielectric constant, dielectric loss, AC conductivity, and breakdown strength of composites films. The composite films load with 10 vol.% 2D Bi2Te3@SiO2 nanosheets exhibits a high dielectric constant of 70.3 at 1 kHz and relatively low dielectric loss of 0.058 at 1 kHz. The finite element simulation of electric field and electric current density distribution revealed that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the energy loss, local electric field strength, and breakdown strength of composite films. Therefore, this work will provide a promising route to achieve high-performance capacitors.

Room temperature strong light-matter coupling in three dimensional terahertz meta-atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paulillo, B., E-mail: bruno.paulillo@u-psud.fr; Manceau, J.-M., E-mail: jean-michel.manceau@u-psud.fr; Colombelli, R., E-mail: raffaele.colombelli@u-psud.fr

2016-03-07

We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice themore » Rabi frequency (2Ω{sub Rabi}), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperature.« less

Pseudo-Jahn-Teller Distortion in Two-Dimensional Phosphorus: Origin of Black and Blue Phases of Phosphorene and Band Gap Modulation by Molecular Charge Transfer.

PubMed

Chowdhury, Chandra; Jahiruddin, Sheik; Datta, Ayan

2016-04-07

Phosphorene (Pn) is stabilized as a layered material like graphite, yet it possess a natural direct band gap (Eg = 2.0 eV). Interestingly, unlike graphene, Pn exhibits a much richer phase diagram which includes distorted forms like the stapler-clip (black Pn, α form) and chairlike (blue Pn, β form) structures. The existence of these phases is attributed to pseudo-Jahn-Teller (PJT) instability of planar hexagonal P6(6-) rings. In both cases, the condition for vibronic instability of the planar P6(6-) rings is satisfied. Doping with electron donors like tetrathiafulvalene and tetraamino-tetrathiafulvalene and electron acceptors like tetracyanoquinodimethane and tetracyanoethylene convert blue Pn into N-type and black Pn into efficient P-type semiconductors, respectively. Interestingly, pristine blue Pn, an indirect gap semiconductor, gets converted into a direct gap semiconductor on electron or hole doping. Because of comparatively smaller undulation in blue Pn (with respect to black Pn), the van der Waals interactions between the dopants and blue Pn is stronger. PJT distortions for two-dimensional phosphorus provides a unified understanding of structural features and chemical reactivity in its different phases.

Ultrafast all-optical imaging technique using low-temperature grown GaAs/AlxGa1 - xAs multiple-quantum-well semiconductor

NASA Astrophysics Data System (ADS)

Gao, Guilong; Tian, Jinshou; Wang, Tao; He, Kai; Zhang, Chunmin; Zhang, Jun; Chen, Shaorong; Jia, Hui; Yuan, Fenfang; Liang, Lingliang; Yan, Xin; Li, Shaohui; Wang, Chao; Yin, Fei

2017-11-01

We report and experimentally demonstrate an ultrafast all-optical imaging technique capable of single-shot ultrafast recording with a picosecond-scale temporal resolution and a micron-order two-dimensional spatial resolution. A GaAs/AlxGa1 - xAs multiple-quantum-well (MQW) semiconductor with a picosecond response time, grown using molecular beam epitaxy (MBE) at a low temperature (LT), is used for the first time in ultrafast imaging technology. The semiconductor transforms the signal beam information to the probe beam, the birefringent delay crystal time-serializes the input probe beam, and the beam displacer maps different polarization probe beams onto different detector locations, resulting in two frames with an approximately 9 ps temporal separation and approximately 25 lp/mm spatial resolution in the visible range.

A splitting scheme based on the space-time CE/SE method for solving multi-dimensional hydrodynamical models of semiconductor devices

NASA Astrophysics Data System (ADS)

Nisar, Ubaid Ahmed; Ashraf, Waqas; Qamar, Shamsul

2016-08-01

Numerical solutions of the hydrodynamical model of semiconductor devices are presented in one and two-space dimension. The model describes the charge transport in semiconductor devices. Mathematically, the models can be written as a convection-diffusion type system with a right hand side describing the relaxation effects and interaction with a self consistent electric field. The proposed numerical scheme is a splitting scheme based on the conservation element and solution element (CE/SE) method for hyperbolic step, and a semi-implicit scheme for the relaxation step. The numerical results of the suggested scheme are compared with the splitting scheme based on Nessyahu-Tadmor (NT) central scheme for convection step and the same semi-implicit scheme for the relaxation step. The effects of various parameters such as low field mobility, device length, lattice temperature and voltages for one-space dimensional hydrodynamic model are explored to further validate the generic applicability of the CE/SE method for the current model equations. A two dimensional simulation is also performed by CE/SE method for a MESFET device, producing results in good agreement with those obtained by NT-central scheme.

On the application of quantum transport theory to electron sources.

PubMed

Jensen, Kevin L

2003-01-01

Electron sources (e.g., field emitter arrays, wide band-gap (WBG) semiconductor materials and coatings, carbon nanotubes, etc.) seek to exploit ballistic transport within the vacuum after emission from microfabricated structures. Regardless of kind, all sources strive to minimize the barrier to electron emission by engineering material properties (work function/electron affinity) or physical geometry (field enhancement) of the cathode. The unique capabilities of cold cathodes, such as instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, cold emission, small size and/or low voltage operation characteristics, commend their use in several advanced devices when physical size, weight, power consumption, beam current, and pulse repletion frequency are important, e.g., RF power amplifier such as traveling wave tubes (TWTs) for radar and communications, electrodynamic tethers for satellite deboost/reboost, and electric propulsion systems such as Hall thrusters for small satellites. The theoretical program described herein is directed towards models to evaluate emission current from electron sources (in particular, emission from WBG and Spindt-type field emitter) in order to assess their utility, capabilities and performance characteristics. Modeling efforts particularly include: band bending, non-linear and resonant (Poole-Frenkel) potentials, the extension of one-dimensional theory to multi-dimensional structures, and emission site statistics due to variations in geometry and the presence of adsorbates. Two particular methodologies, namely, the modified Airy approach and metal-semiconductor statistical hyperbolic/ellipsoidal model, are described in detail in their present stage of development.

Cathodoluminescence study of one-dimensional free-standing widegap-semiconductor nanostructures: GaN nanotubes, Si3N4 nanobelts and ZnS/Si nanowires.

PubMed

Sekiguchi, Takashi; Hu, Junqing; Bando, Yoshio

2004-01-01

Luminescence properties of one-dimensional free-standing widegap-semiconductor nanostructures were characterized by means of cathodoluminescence (CL). GaN nanopipes, alpha-Si3N4 nanobelts and ZnS/Si nanowires were fabricated by a catalyst-free method, namely grown in an induction furnace from powders. After the observation of morphology by scanning electron microscopy as well as the confirmation of their crystal structures by transmission electron microscopy, their CL spectra and images were observed. The CL spectra mapping as well as the monochromatic CL imaging revealed the variation of the luminescence spectra of different nanowires as well as that along a single wire. These results revealed the optical features of nanostructures.

Extreme Soft Limit Observation of Quantum Hall Effect in a 3-d Semiconductor

NASA Astrophysics Data System (ADS)

Bleiweiss, Michael; Yin, Ming; Amirzadeh, Jafar; Preston, Harry; Datta, Timir

2004-03-01

We report on the evidence for quantum hall effect at 38K and in magnetic fields (B) as low as 1k-Orsted. Our specimens were semiconducting, carbon replica opal (CRO) structures. CRO are three dimensional bulk systems where the carbon is grown by CVD into the porous regions in artificial silica opals. The carbon forms layers on top of the silica spheres as eggshells. The shells are of uneven thickness and are perforated at the contacts points of the opal spheres and form a closed packed, three dimensional crystal structure. Plateaus in inverse R_xy that are conjugated with well-defined Subnikov-deHass modulations in R_xx were observed. The quantum steps that are particularly prominent were the states with fill factors v = p/q (p,q are integers) were the well know fractions, 1/3, 1/2, 3/5, 1 and 5/2. QHE steps indicate that the carriers are localized in two-dimensional regions, which may be due to the extremely large surface to volume ratio associated with replica opal structure. From the B-1 vs v straight line, the effective surface carrier density, ns = 2.2 x 10^14 m-2. To the best of our knowledge, the current work is the first to report fractional quantum hall plateaus in a bulk system.

Magneto-optical Faraday rotation of semiconductor nanoparticles embedded in dielectric matrices.

PubMed

Savchuk, Andriy I; Stolyarchuk, Ihor D; Makoviy, Vitaliy V; Savchuk, Oleksandr A

2014-04-01

Faraday rotation has been studied for CdS, CdTe, and CdS:Mn semiconductor nanoparticles synthesized by colloidal chemistry methods. Additionally these materials were prepared in a form of semiconductor nanoparticles embedded in polyvinyl alcohol films. Transmission electron microscopy and atomic force microscopy analyses served as confirmation of nanocrystallinity and estimation of the average size of the nanoparticles. Spectral dependence of the Faraday rotation for the studied nanocrystals and nanocomposites is correlated with a blueshift of the absorption edge due to the confinement effect in zero-dimensional structures. Faraday rotation spectra and their temperature behavior in Mn-doped nanocrystals demonstrates peculiarities, which are associated with s, p-d exchange interaction between Mn²⁺ ions and band carriers in diluted magnetic semiconductor nanostructures.

High performance thermoelectric materials and methods of preparation

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1997-01-01

Transition metals (T) of Group VIII (Co, Rh and Ir) have been prepared as semiconductor alloys with Sb having the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor alloys and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor alloys having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freeze techniques, liquid-solid phase sintering techniques, low temperature powder sintering and/or hot-pressing. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 8000 cm.sup.2.V.sup.-1.s.sup.-1), good Seebeck coefficients (up to 400 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.), and low thermal conductivities (as low as 15 mW/cmK). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a two fold increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

Schottky nanocontact of one-dimensional semiconductor nanostructures probed by using conductive atomic force microscopy

NASA Astrophysics Data System (ADS)

Lee, Jung Ah; Rok Lim, Young; Jung, Chan Su; Choi, Jun Hee; Im, Hyung Soon; Park, Kidong; Park, Jeunghee; Kim, Gyu Tae

2016-10-01

To develop the advanced electronic devices, the surface/interface of each component must be carefully considered. Here, we investigate the electrical properties of metal-semiconductor nanoscale junction using conductive atomic force microscopy (C-AFM). Single-crystalline CdS, CdSe, and ZnO one-dimensional nanostructures are synthesized via chemical vapor transport, and individual nanobelts (or nanowires) are used to fabricate nanojunction electrodes. The current-voltage (I -V) curves are obtained by placing a C-AFM metal (PtIr) tip as a movable contact on the nanobelt (or nanowire), and often exhibit a resistive switching behavior that is rationalized by the Schottky (high resistance state) and ohmic (low resistance state) contacts between the metal and semiconductor. We obtain the Schottky barrier height and the ideality factor through fitting analysis of the I-V curves. The present nanojunction devices exhibit a lower Schottky barrier height and a higher ideality factor than those of the bulk materials, which is consistent with the findings of previous works on nanostructures. It is shown that C-AFM is a powerful tool for characterization of the Schottky contact of conducting channels between semiconductor nanostructures and metal electrodes.

Nanometer-scale oxide thin film transistor with potential for high-density image sensor applications.

PubMed

Jeon, Sanghun; Park, Sungho; Song, Ihun; Hur, Ji-Hyun; Park, Jaechul; Kim, Hojung; Kim, Sunil; Kim, Sangwook; Yin, Huaxiang; Chung, U-In; Lee, Eunha; Kim, Changjung

2011-01-01

The integration of electronically active oxide components onto silicon circuits represents an innovative approach to improving the functionality of novel devices. Like most semiconductor devices, complementary-metal-oxide-semiconductor image sensors (CISs) have physical limitations when progressively scaled down to extremely small dimensions. In this paper, we propose a novel hybrid CIS architecture that is based on the combination of nanometer-scale amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and a conventional Si photo diode (PD). With this approach, we aim to overcome the loss of quantum efficiency and image quality due to the continuous miniaturization of PDs. Specifically, the a-IGZO TFT with 180 nm gate length is probed to exhibit remarkable performance including low 1/f noise and high output gain, despite fabrication temperatures as low as 200 °C. In particular, excellent device performance is achieved using a double-layer gate dielectric (Al₂O₃/SiO₂) combined with a trapezoidal active region formed by a tailored etching process. A self-aligned top gate structure is adopted to ensure low parasitic capacitance. Lastly, three-dimensional (3D) process simulation tools are employed to optimize the four-pixel CIS structure. The results demonstrate how our stacked hybrid device could be the starting point for new device strategies in image sensor architectures. Furthermore, we expect the proposed approach to be applicable to a wide range of micro- and nanoelectronic devices and systems.

Hydrogenated arsenenes as planar magnet and Dirac material

NASA Astrophysics Data System (ADS)

Zhang, Shengli; Hu, Yonghong; Hu, Ziyu; Cai, Bo; Zeng, Haibo

2015-07-01

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Shengli; Cai, Bo; Zeng, Haibo, E-mail: Huziyu@csrc.ac.cn, E-mail: zeng.haibo@njust.edu.cn

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating frommore » wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.« less

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutherland, Kevin Jerome

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronicmore » devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.« less

Enhanced photocatalytic hydrogen production on three-dimensional gold butterfly wing scales/CdS nanoparticles

NASA Astrophysics Data System (ADS)

Fang, Jing; Song, Guofen; Liu, Qinglei; Zhang, Wang; Gu, Jiajun; Su, Yishi; Su, Huilan; Guo, Cuiping; Zhang, Di

2018-01-01

Photocatalytic water splitting via utilizing various semiconductors is recognized as a promising way for hydrogen production. Plasmonic metals with sub-micrometer textures can improve the photocatalytic performance of semiconductors via a localized surface plasmon resonance (LSPR) process. Moreover, arrays of multilayer metallic structures can help generate strong LSPR. However, artificial synthesis has difficulties in constructing novel multilayer metallic arrays down to nanoscales. Here, we use three dimensional (3D) scales from Morpho didius forewings (M) to prepare 3D Au-wings with intact hierarchical bio-structures. For comparison, we use Troides helena forewings (T) which are known for their antireflection quasi-honeycomb structures resulting in strong light absorbing ability. Results show that multilayer rib structures of Au-M can significantly amplify the LSPR of 3D Au and thus can efficiently help the photocatalytic process (9-fold increase). This amplification effect is obviously more superior to the straightforward enhancement of the absorption of incident light (Au-T, 5-fold increase). Thus, our study provides the possibility to prepare highly efficient plasmonic photocatalysts (possessing 3D multilayer rib structures) via an easy method. This work will also be revealing for plasmonic applications in other fields.

High resolution three-dimensional doping profiler

DOEpatents

Thundat, Thomas G.; Warmack, Robert J.

1999-01-01

A semiconductor doping profiler provides a Schottky contact at one surface and an ohmic contact at the other. While the two contacts are coupled to a power source, thereby establishing an electrical bias in the semiconductor, a localized light source illuminates the semiconductor to induce a photocurrent. The photocurrent changes in accordance with the doping characteristics of the semiconductor in the illuminated region. By changing the voltage of the power source the depth of the depletion layer can be varied to provide a three dimensional view of the local properties of the semiconductor.

Methods of producing strain in a semiconductor waveguide and related devices

DOEpatents

Cox, Johathan Albert; Rakich, Peter Thomas

2016-02-16

Quasi-phase matched (QPM), semiconductor photonic waveguides include periodically-poled alternating first and second sections. The first sections exhibit a high degree of optical coupling (abbreviated "X.sup.2"), while the second sections have a low X.sup.2. The alternating first and second sections may comprise high-strain and low-strain sections made of different material states (such as crystalline and amorphous material states) that exhibit high and low X.sup.2 properties when formed on a particular substrate, and/or strained corrugated sections of different widths. The QPM semiconductor waveguides may be implemented as silicon-on-insulator (SOI), or germanium-on-silicon structures compatible with standard CMOS processes, or as silicon-on-sapphire (SOS) structures.

Light-Immune pH Sensor with SiC-Based Electrolyte-Insulator-Semiconductor Structure

NASA Astrophysics Data System (ADS)

Lin, Yi-Ting; Huang, Chien-Shiang; Chow, Lee; Lan, Jyun-Ming; Yang, Chia-Ming; Chang, Liann-Be; Lai, Chao-Sung

2013-12-01

An electrolyte-insulator-semiconductor (EIS) structure with high-band-gap semiconductor of silicon carbide is demonstrated as a pH sensor in this report. Two different sensing membranes, i.e., gadolinium oxide (Gd2O3) and hafnium oxide (HfO2), were investigated. The HfO2 film deposited by atomic layer deposition (ALD) at low temperature shows high pH sensing properties with a sensitivity of 52.35 mV/pH and a low signal of 4.95 mV due to light interference. The EIS structures with silicon carbide can provide better visible light immunity due to its high band gap that allows pH detection in an outdoor environment without degradation of pH sensitivity.

Polarization-Resolved Study of High Harmonics from Bulk Semiconductors

NASA Astrophysics Data System (ADS)

Kaneshima, Keisuke; Shinohara, Yasushi; Takeuchi, Kengo; Ishii, Nobuhisa; Imasaka, Kotaro; Kaji, Tomohiro; Ashihara, Satoshi; Ishikawa, Kenichi L.; Itatani, Jiro

2018-06-01

The polarization property of high harmonics from gallium selenide is investigated using linearly polarized midinfrared laser pulses. With a high electric field, the perpendicular polarization component of the odd harmonics emerges, which is not present with a low electric field and cannot be explained by the perturbative nonlinear optics. A two-dimensional single-band model is developed to show that the anisotropic curvature of an energy band of solids, which is pronounced in an outer part of the Brillouin zone, induces the generation of the perpendicular odd harmonics. This model is validated by three-dimensional quantum mechanical simulations, which reproduce the orientation dependence of the odd-order harmonics. The quantum mechanical simulations also reveal that the odd- and even-order harmonics are produced predominantly by the intraband current and interband polarization, respectively. These experimental and theoretical demonstrations clearly show a strong link between the band structure of a solid and the polarization property of the odd-order harmonics.

Rashba effect in single-layer antimony telluroiodide SbTeI

DOE PAGES

Zhuang, Houlong L.; Cooper, Valentino R.; Xu, Haixuan; ...

2015-09-04

Exploring spin-orbit coupling (SOC) in single-layer materials is important for potential spintronics applications. In this paper, using first-principles calculations, we show that single-layer antimony telluroiodide SbTeI behaves as a two-dimensional semiconductor exhibiting a G 0W 0 band gap of 1.82 eV. More importantly, we observe the Rashba spin splitting in the SOC band structure of single-layer SbTeI with a sizable Rashba coupling parameter of 1.39 eV Å, which is significantly larger than that of a number of two-dimensional systems including surfaces and interfaces. The low formation energy and real phonon modes of single-layer SbTeI imply that it is stable. Finally,more » our study suggests that single-layer SbTeI is a candidate single-layer material for applications in spintronics devices.« less

Carrier Injection and Scattering in Atomically Thin Chalcogenides

NASA Astrophysics Data System (ADS)

Li, Song-Lin; Tsukagoshi, Kazuhito

2015-12-01

Atomically thin two-dimensional chalcogenides such as MoS2 monolayers are structurally ideal channel materials for the ultimate atomic electronics. However, a heavy thickness dependence of electrical performance is shown in these ultrathin materials, and the device performance normally degrades while exhibiting a low carrier mobility as compared with corresponding bulks, constituting a main hurdle for application in electronics. In this brief review, we summarize our recent work on electrode/channel contacts and carrier scattering mechanisms to address the origins of this adverse thickness dependence. Extrinsically, the Schottky barrier height increases at the electrode/channel contact area in thin channels owing to bandgap expansion caused by quantum confinement, which hinders carrier injection and degrades device performance. Intrinsically, thin channels tend to suffer from intensified Coulomb impurity scattering, resulting from the reduced interaction distance between interfacial impurities and channel carriers. Both factors are responsible for the adverse dependence of carrier mobility on channel thickness in two-dimensional semiconductors.

2D Crystal heterostructures properties and growth by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Xing, Grace Huili

Two-dimensional (2D) crystals such as transition metal dichalcogenides (TMDs) along with other families of layered materials including graphene, SnSe2, GaSe, BN etc, has attracted intense attention from the scientific community. One monolayer of such materials represent the thinnest ``quantum wells''. These layered materials typically possess an in-plane hexagonal crystal structure, and can be stacked together by interlayer van der Waals interactions. Therefore, it is possible to create novel heterostructures by stacking materials with large lattice mismatches and different properties, for instance, superconductors (NbSe2) , metals, semi-metals (graphene), semiconductors (MoS2) and insulators (BN). Numerous novel material properties and device concepts have been discovered, proposed and demonstrated lately. However, the low internal photoluminescence efficiency (IPE, <1%) and low carrier mobility observed in the 2D semiconductors suggest strongly that the materials under investigation today most likely suffer from a high concentration of defects. In this talk, I will share our progress and the challenges we face in terms of preparing, characterizing these 2D crystals as well as pursuing their applications. This work has been supported in part by NSF, AFOSR and LEAST, one of the STARnet centers.

Pressure-induced structural and semiconductor-semiconductor transitions in C o0.5M g0.5C r2O4

NASA Astrophysics Data System (ADS)

Rahman, S.; Saqib, Hajra; Zhang, Jinbo; Errandonea, D.; Menéndez, C.; Cazorla, C.; Samanta, Sudeshna; Li, Xiaodong; Lu, Junling; Wang, Lin

2018-05-01

The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel C o0.5M g0.5C r2O4 was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, F d 3 ¯m ) and underwent a pressure-induced structural transition to a tetragonal phase (space group I 4 ¯m 2 ) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures with the existence of a low-pressure (LP) phase and started to increase with the emergence of a high-pressure (HP) phase. The temperature dependent resistivity experiments at different pressures illustrated the wide band gap semiconducting nature of both the LP and HP phases with different activation energies, suggesting a semiconductor-semiconductor transition at HP. No evidence of chemical decomposition or a semiconductor-metal transition was observed in our studies.

Metal-chelate dye-controlled organization of Cd32S14(SPh)40(4-) nanoclusters into three-dimensional molecular and covalent open architecture.

PubMed

Zheng, Nanfeng; Lu, Haiwei; Bu, Xianhui; Feng, Pingyun

2006-04-12

Chalcogenide II-VI nanoclusters are usually prepared as isolated clusters and have defied numerous efforts to join them into covalent open-framework architecture with conventional templating methods such as protonated amines or inorganic cations commonly used to direct the formation of porous frameworks. Herein, we report the first templated synthesis of II-VI covalent superlattices from large II-VI tetrahedral clusters (i.e., [Cd32S14(SPh)38]2-). Our method takes advantage of low charge density of metal-chelate dyes that is a unique match with three-dimensional II-VI semiconductor frameworks in charge density, surface hydrophilicity-hydrophobicity, and spatial organization. In addition, metal-chelate dyes also serve to tune the optical properties of resulting dye semiconductor composite materials.

Graphitic carbon nitride based nanocomposites: a review

NASA Astrophysics Data System (ADS)

Zhao, Zaiwang; Sun, Yanjuan; Dong, Fan

2014-11-01

Graphitic carbon nitride (g-C3N4), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C3N4 suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C3N4 could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C3N4-based nanocomposites can be classified and summarized: namely, the g-C3N4 based metal-free heterojunction, the g-C3N4/single metal oxide (metal sulfide) heterojunction, g-C3N4/composite oxide, the g-C3N4/halide heterojunction, g-C3N4/noble metal heterostructures, and the g-C3N4 based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C3N4-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C3N4-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C3N4-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C3N4-based advanced nanomaterials.

Structural tunability and switchable exciton emission in inorganic-organic hybrids with mixed halides

NASA Astrophysics Data System (ADS)

Ahmad, Shahab; Baumberg, Jeremy J.; Vijaya Prakash, G.

2013-12-01

Room-temperature tunable excitonic photoluminescence is demonstrated in alloy-tuned layered Inorganic-Organic (IO) hybrids, (C12H25NH3)2PbI4(1-y)Br4y (y = 0 to 1). These perovskite IO hybrids adopt structures with alternating stacks of low-dimensional inorganic and organic layers, considered to be naturally self-assembled multiple quantum wells. These systems resemble stacked monolayer 2D semiconductors since no interlayer coupling exists. Thin films of IO hybrids exhibit sharp and strong photoluminescence (PL) at room-temperature due to stable excitons formed within the low-dimensional inorganic layers. Systematic variation in the observed exciton PL from 510 nm to 350 nm as the alloy composition is changed, is attributed to the structural readjustment of crystal packing upon increase of the Br content in the Pb-I inorganic network. The energy separation between exciton absorption and PL is attributed to the modified exciton density of states and diffusion of excitons from relatively higher energy states corresponding to bromine rich sites towards the lower energy iodine sites. Apart from compositional fluctuations, these excitons show remarkable reversible flips at temperature-induced phase transitions. All the results are successfully correlated with thermal and structural studies. Such structural engineering flexibility in these hybrids allows selective tuning of desirable exciton properties within suitable operating temperature ranges. Such wide-range PL tunability and reversible exciton switching in these novel IO hybrids paves the way to potential applications in new generation of optoelectronic devices.

Application of kinetic flux vector splitting scheme for solving multi-dimensional hydrodynamical models of semiconductor devices

NASA Astrophysics Data System (ADS)

Nisar, Ubaid Ahmed; Ashraf, Waqas; Qamar, Shamsul

In this article, one and two-dimensional hydrodynamical models of semiconductor devices are numerically investigated. The models treat the propagation of electrons in a semiconductor device as the flow of a charged compressible fluid. It plays an important role in predicting the behavior of electron flow in semiconductor devices. Mathematically, the governing equations form a convection-diffusion type system with a right hand side describing the relaxation effects and interaction with a self consistent electric field. The proposed numerical scheme is a splitting scheme based on the kinetic flux-vector splitting (KFVS) method for the hyperbolic step, and a semi-implicit Runge-Kutta method for the relaxation step. The KFVS method is based on the direct splitting of macroscopic flux functions of the system on the cell interfaces. The second order accuracy of the scheme is achieved by using MUSCL-type initial reconstruction and Runge-Kutta time stepping method. Several case studies are considered. For validation, the results of current scheme are compared with those obtained from the splitting scheme based on the NT central scheme. The effects of various parameters such as low field mobility, device length, lattice temperature and voltage are analyzed. The accuracy, efficiency and simplicity of the proposed KFVS scheme validates its generic applicability to the given model equations. A two dimensional simulation is also performed by KFVS method for a MESFET device, producing results in good agreement with those obtained by NT-central scheme.

Two-dimensional wide-band-gap II-V semiconductors with a dilated graphene-like structure

NASA Astrophysics Data System (ADS)

Zhang, Xue-Jing; Liu, Bang-Gui

2016-12-01

Since the advent of graphene, two-dimensional (2D) materials have become very attractive and there is growing interest in exploring new 2D materials beyond graphene. Here, through density-functional theory (DFT) calculations, we predict 2D wide-band-gap II-V semiconductor materials of M3X2 (M = Zn, Cd and X = N, P, As) with a dilated graphene-like honeycomb structure. In this structure the group-V X atoms form two X-atomic planes symmetrically astride the centering group-IIB M atomic plane. Our DFT calculation shows that 2D Zn3N2, Zn3P2 and Zn3As2 have direct band gaps of 2.87, 3.81 and 3.55 eV, respectively, and 2D Cd3N2, Cd3P2 and Cd3As2 exhibit indirect band gaps of 2.74, 3.51 and 3.29 eV, respectively. Each of the six 2D materials is shown to have effective carrier (either hole or electron) masses down to 0.03m 0-0.05m 0. The structural stability and feasibility of experimental realization of these 2D materials has been shown in terms of DFT phonon spectra and total energy comparison with related existing bulk materials. On the experimental side, there already are many similar two-coordinate structures of Zn and other transition metals in various organic materials. Therefore, these 2D semiconductors can enrich the family of 2D electronic materials and may have promising potential for achieving novel transistors and optoelectronic devices.

Surface Plasmon Polariton-Assisted Long-Range Exciton Transport in Monolayer Semiconductor Lateral Heterostructure

NASA Astrophysics Data System (ADS)

Shi, Jinwei; Lin, Meng-Hsien; Chen, Yi-Tong; Estakhri, Nasim Mohammadi; Tseng, Guo-Wei; Wang, Yanrong; Chen, Hung-Ying; Chen, Chun-An; Shih, Chih-Kang; Alã¹, Andrea; Li, Xiaoqin; Lee, Yi-Hsien; Gwo, Shangjr

Recently, two-dimensional (2D) semiconductor heterostructures, i.e., atomically thin lateral heterostructures (LHSs) based on transition metal dichalcogenides (TMDs) have been demonstrated. In an optically excited LHS, exciton transport is typically limited to a rather short spatial range ( 1 micron). Furthermore, additional losses may occur at the lateral interfacial regions. Here, to overcome these challenges, we experimentally implement a planar metal-oxide-semiconductor (MOS) structure by placing a monolayer of WS2/MoS2 LHS on top of an Al2O3 capped Ag single-crystalline plate. We found that the exciton transport range can be extended to tens of microns. The process of long-range exciton transport in the MOS structure is confirmed to be mediated by an exciton-surface plasmon polariton-exciton conversion mechanism, which allows a cascaded energy transfer process. Thus, the planar MOS structure provides a platform seamlessly combining 2D light-emitting materials with plasmonic planar waveguides, offering great potential for developing integrated photonic/plasmonic functionalities.

Strain engineering on electronic structure and carrier mobility in monolayer GeP3

NASA Astrophysics Data System (ADS)

Zeng, Bowen; Long, Mengqiu; Zhang, Xiaojiao; Dong, Yulan; Li, Mingjun; Yi, Yougen; Duan, Haiming

2018-06-01

Using density functional theory coupled with the Boltzmann transport equation with relaxation time approximation, we have studied the strain effect on the electronic structure and carrier mobility of two-dimensional monolayer GeP3. We find that the energies of valence band maximum and conduction band minimum are nearly linearly shifted with a biaxial strain in the range of  ‑4% to 6%, and the band structure experiences a remarkable transition from semiconductor to metal with the appropriate compression (‑5% strain). Under biaxial strain, the mobility of the electron and hole in monolayer GeP3 reduces and increases by more than one order of magnitude, respectively. It is suggested that it is possible to perform successive transitions from an n-type semiconductor (‑4% strain) to a good performance p-semiconductor (+6% strain) by applying strain in monolayer GeP3, which is potentially useful for flexible electronics and nanosized mechanical sensors.

Charge Separation at Mixed-Dimensional Single and Multilayer MoS2/Silicon Nanowire Heterojunctions.

PubMed

Henning, Alex; Sangwan, Vinod K; Bergeron, Hadallia; Balla, Itamar; Sun, Zhiyuan; Hersam, Mark C; Lauhon, Lincoln J

2018-05-16

Layered two-dimensional (2-D) semiconductors can be combined with other low-dimensional semiconductors to form nonplanar mixed-dimensional van der Waals (vdW) heterojunctions whose charge transport behavior is influenced by the heterojunction geometry, providing a new degree of freedom to engineer device functions. Toward that end, we investigated the photoresponse of Si nanowire/MoS 2 heterojunction diodes with scanning photocurrent microscopy and time-resolved photocurrent measurements. Comparison of n-Si/MoS 2 isotype heterojunctions with p-Si/MoS 2 heterojunction diodes under varying biases shows that the depletion region in the p-n heterojunction promotes exciton dissociation and carrier collection. We measure an instrument-limited response time of 1 μs, which is 10 times faster than the previously reported response times for planar Si/MoS 2 devices, highlighting the advantages of the 1-D/2-D heterojunction. Finite element simulations of device models provide a detailed understanding of how the electrostatics affect charge transport in nanowire/vdW heterojunctions and inform the design of future vdW heterojunction photodetectors and transistors.

Microgravity

NASA Image and Video Library

2004-04-15

A semiconductor's usefulness is determined by how atoms are ordered within the crystal's underlying three-dimensional structure. While this mercury telluride and cadmium telluride alloy sample mixes completely in Earth -based laboratories, convective flows prevent them from mixing uniformly. In space, the ingredients mix more homogenously, resulting in a superior product.

Graphene-based hybrid structures combined with functional materials of ferroelectrics and semiconductors.

PubMed

Jie, Wenjing; Hao, Jianhua

2014-06-21

Fundamental studies and applications of 2-dimensional (2D) graphene may be deepened and broadened via combining graphene sheets with various functional materials, which have been extended from the traditional insulator of SiO2 to a versatile range of dielectrics, semiconductors and metals, as well as organic compounds. Among them, ferroelectric materials have received much attention due to their unique ferroelectric polarization. As a result, many attractive characteristics can be shown in graphene/ferroelectric hybrid systems. On the other hand, graphene can be integrated with conventional semiconductors and some newly-discovered 2D layered materials to form distinct Schottky junctions, yielding fascinating behaviours and exhibiting the potential for various applications in future functional devices. This review article is an attempt to illustrate the most recent progress in the fabrication, operation principle, characterization, and promising applications of graphene-based hybrid structures combined with various functional materials, ranging from ferroelectrics to semiconductors. We focus on mechanically exfoliated and chemical-vapor-deposited graphene sheets integrated in numerous advanced devices. Some typical hybrid structures have been highlighted, aiming at potential applications in non-volatile memories, transparent flexible electrodes, solar cells, photodetectors, and so on.

Graphene-based hybrid structures combined with functional materials of ferroelectrics and semiconductors

NASA Astrophysics Data System (ADS)

Jie, Wenjing; Hao, Jianhua

2014-05-01

Fundamental studies and applications of 2-dimensional (2D) graphene may be deepened and broadened via combining graphene sheets with various functional materials, which have been extended from the traditional insulator of SiO2 to a versatile range of dielectrics, semiconductors and metals, as well as organic compounds. Among them, ferroelectric materials have received much attention due to their unique ferroelectric polarization. As a result, many attractive characteristics can be shown in graphene/ferroelectric hybrid systems. On the other hand, graphene can be integrated with conventional semiconductors and some newly-discovered 2D layered materials to form distinct Schottky junctions, yielding fascinating behaviours and exhibiting the potential for various applications in future functional devices. This review article is an attempt to illustrate the most recent progress in the fabrication, operation principle, characterization, and promising applications of graphene-based hybrid structures combined with various functional materials, ranging from ferroelectrics to semiconductors. We focus on mechanically exfoliated and chemical-vapor-deposited graphene sheets integrated in numerous advanced devices. Some typical hybrid structures have been highlighted, aiming at potential applications in non-volatile memories, transparent flexible electrodes, solar cells, photodetectors, and so on.

Optical Pulse Interactions in Nonlinear Excited State Materials

DTIC Science & Technology

2008-07-14

described below. 2.5 Overview of Semiconductor Quantum Dot A quantum dot (QD) is a quasi -zero-dimensional object where the carrier movement is...a particle of mass M (e.g., an electron) having a potential energy can be described by a wavefunction that satisfies the following Schrödinger...dot (QD) is a quasi -zero-dimensional object where the carrier movement is restricted in three dimensions. The bulk crystalline structure of the

Printable semiconductor structures and related methods of making and assembling

DOEpatents

Nuzzo, Ralph G.; Rogers, John A.; Menard, Etienne; Lee, Keon Jae; Khang; , Dahl-Young; Sun, Yugang; Meitl, Matthew; Zhu, Zhengtao; Ko, Heung Cho; Mack, Shawn

2013-03-12

The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

Printable semiconductor structures and related methods of making and assembling

DOEpatents

Nuzzo, Ralph G [Champaign, IL; Rogers, John A [Champaign, IL; Menard, Etienne [Durham, NC; Lee, Keon Jae [Tokyo, JP; Khang, Dahl-Young [Urbana, IL; Sun, Yugang [Westmont, IL; Meitl, Matthew [Raleigh, NC; Zhu, Zhengtao [Rapid City, SD; Ko, Heung Cho [Urbana, IL; Mack, Shawn [Goleta, CA

2011-10-18

The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

Printable semiconductor structures and related methods of making and assembling

DOEpatents

Nuzzo, Ralph G.; Rogers, John A.; Menard, Etienne; Lee, Keon Jae; Khang, Dahl-Young; Sun, Yugang; Meitl, Matthew; Zhu, Zhengtao; Ko, Heung Cho; Mack, Shawn

2010-09-21

The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

Genetic algorithm prediction of two-dimensional group-IV dioxides for dielectrics

NASA Astrophysics Data System (ADS)

Singh, Arunima K.; Revard, Benjamin C.; Ramanathan, Rohit; Ashton, Michael; Tavazza, Francesca; Hennig, Richard G.

2017-04-01

Two-dimensional (2D) materials present a new class of materials whose structures and properties can differ from their bulk counterparts. We perform a genetic algorithm structure search using density-functional theory to identify low-energy structures of 2D group-IV dioxides A O2 (A =Si , Ge, Sn, Pb). We find that 2D SiO2 is most stable in the experimentally determined bi-tetrahedral structure, while 2D SnO2 and PbO2 are most stable in the 1 T structure. For 2D GeO2, the genetic algorithm finds a new low-energy 2D structure with monoclinic symmetry. Each system exhibits 2D structures with formation energies ranging from 26 to 151 meV/atom, below those of certain already synthesized 2D materials. The phonon spectra confirm their dynamic stability. Using the HSE06 hybrid functional, we determine that the 2D dioxides are insulators or semiconductors, with a direct band gap of 7.2 eV at Γ for 2D SiO2, and indirect band gaps of 4.8-2.7 eV for the other dioxides. To guide future applications of these 2D materials in nanoelectronic devices, we determine their band-edge alignment with graphene, phosphorene, and single-layer BN and MoS2. An assessment of the dielectric properties and electrochemical stability of the 2D group-IV dioxides shows that 2D GeO2 and SnO2 are particularly promising candidates for gate oxides and 2D SnO2 also as a protective layer in heterostructure nanoelectronic devices.

Colloidal nanocrystals as LEGO® bricks for building electronic band structure models.

PubMed

Tadjine, Athmane; Delerue, Christophe

2018-03-28

The synthesis of self-assembled semiconductor nanocrystal (NC) superlattices using oriented attachment recently became a flourishing research topic. This technique already produced remarkable forms of NC superlattices, such as linear chains, mono and multilayer square lattices, and silicene-like honeycomb lattices. In the case of lead chalcogenide semiconductors where NCs are in the form of truncated nanocubes, the attachment mostly occurs via (100) facets. In this work, we show that all these structures can be seen as sub-structures of a simple cubic lattice. From this, we investigate a rich variety of one-dimensional or two-dimensional superlattices that could be built as few lines or few layers taken from the same cubic system following different crystallographic orientations. Each NC can be therefore considered as a LEGO® brick, and any superlattice can be obtained from another one by rearranging the bricks. Moreover, we show that this concept of LEGO® bricks can be extended to the calculation of the electronic band structure of the superlattices. This leads to a simple yet powerful way to build analytical Hamiltonians that present band structures in excellent agreement with more elaborate atomistic tight-binding calculations. This LEGO® concept could guide the synthesis of superlattices and LEGO® Hamiltonians should greatly simplify further studies on the (opto-)electronic properties of such structures.

Plasma Properties of an Exploding Semiconductor Igniter

NASA Astrophysics Data System (ADS)

McGuirk, J. S.; Thomas, K. A.; Shaffer, E.; Malone, A. L.; Baginski, T.; Baginski, M. E.

1997-11-01

Requirements by the automotive industry for low-cost, pyrotechnic igniters for automotive airbags have led to the development of several semiconductor devices. The properties of the plasma produced by the vaporization of an exploding semiconductor are necessary in order to minimize the electrical energy requirements. This work considers two silicon-based semiconductor devices: the semiconductor bridge (SCB) and the semiconductor junction igniter both consisting of etched silicon with vapor deposited aluminum structures. Electrical current passing through the device heats a narrow junction region to the point of vaporization creating an aluminum and silicon low-temperature plasma. This work will investigate the electrical characteristics of both devices and infer the plasma properties. Furthermore optical spectral measurements will be taken of the exploding devices to estimate the temperature and density of the plasma.

Quantum theory of the electronic and optical properties of low-dimensional semiconductor systems

NASA Astrophysics Data System (ADS)

Lau, Wayne Heung

This thesis examines the electronic and optical properties of low-dimensional semiconductor systems. A theory is developed to study the electron-hole generation-recombination process of type-II semimetallic semiconductor heterojunctions based on a 3 x 3 k·p matrix Hamiltonian (three-band model) and an 8 x 8 k·p matrix Hamiltonian (eight-band model). A novel electron-hole generation and recombination process, which is called activationless generation-recombination process, is predicted. It is demonstrated that the current through the type-II semimetallic semiconductor heterojunctions is governed by the activationless electron-hole generation-recombination process at the heterointerfaces, and that the current-voltage characteristics are essentially linear. A qualitative agreement between theory and experiments is observed. The numerical results of the eight-band model are compared with those of the threeband model. Based on a lattice gas model, a theory is developed to study the influence of a random potential on the ionization equilibrium conditions for bound electron-hole pairs (excitons) in III--V semiconductor heterostructures. It is demonstrated that ionization equilibrium conditions for bound electron-hole pairs change drastically in the presence of strong disorder. It is predicted that strong disorder promotes dissociation of excitons in III--V semiconductor heterostructures. A theory of polariton (photon dressed by phonon) spontaneous emission in a III--V semiconductor doped with semiconductor quantum dots (QDs) or quantum wells (QWs) is developed. For the first time, superradiant and subradiant polariton spontaneous emission phenomena in a polariton-QD (QW) coupled system are predicted when the resonance energies of the two identical QDs (QWs) lie outside the polaritonic energy gap. It is also predicted that when the resonance energies of the two identical QDs (QWs) lie inside the polaritonic energy gap, spontaneous emission of polariton in the polariton-QD (QW) coupled system is inhibited and polariton bound states are formed within the polaritonic energy gap. A theory is also developed to study the polariton eigenenergy spectrum, polariton effective mass, and polariton spectral density of N identical semiconductor QDs (QWs) or a superlattice (SL) placed inside a III--V semiconductor. A polariton-impurity band lying within the polaritonic energy gap of the III--V semiconductor is predicted when the resonance energies of the QDs (QWs) lie inside the polaritonic energy gap. Hole-like polariton effective mass of the polariton-impurity band is predicted. It is also predicted that the spectral density of the polariton has a Lorentzian shape if the resonance energies of the QDs (QWs) lie outside the polaritonic gap.

Trade-Offs in Thin Film Solar Cells with Layered Chalcostibite Photovoltaic Absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Welch, Adam W.; Baranowski, Lauryn L.; Peng, Haowei

Discovery of novel semiconducting materials is needed for solar energy conversion and other optoelectronic applications. However, emerging low-dimensional solar absorbers often have unconventional crystal structures and unusual combinations of optical absorption and electrical transport properties, which considerably slows down the research and development progress. Here, the effect of stronger absorption and weaker carrier collection of 2D-like absorber materials are studied using a high-throughput combinatorial experimental approach, complemented by advanced characterization and computations. It is found that the photoexcited charge carrier collection in CuSbSe 2 solar cells is enhanced by drift in an electric field, addressing a different absorption/collection balance. Themore » resulting drift solar cells efficiency is <5% due to inherent J SC/ V OC trade-off, suggesting that improved carrier diffusion and better contacts are needed to further increase the CuSbSe 2 performance. Furthermore, this study also illustrates the advantages of high-throughput experimental methods for fast optimization of the optoelectronic devices based on emerging low-dimensional semiconductor materials.« less

Trade-Offs in Thin Film Solar Cells with Layered Chalcostibite Photovoltaic Absorbers

DOE PAGES

Welch, Adam W.; Baranowski, Lauryn L.; Peng, Haowei; ...

2017-01-25

Discovery of novel semiconducting materials is needed for solar energy conversion and other optoelectronic applications. However, emerging low-dimensional solar absorbers often have unconventional crystal structures and unusual combinations of optical absorption and electrical transport properties, which considerably slows down the research and development progress. Here, the effect of stronger absorption and weaker carrier collection of 2D-like absorber materials are studied using a high-throughput combinatorial experimental approach, complemented by advanced characterization and computations. It is found that the photoexcited charge carrier collection in CuSbSe 2 solar cells is enhanced by drift in an electric field, addressing a different absorption/collection balance. Themore » resulting drift solar cells efficiency is <5% due to inherent J SC/ V OC trade-off, suggesting that improved carrier diffusion and better contacts are needed to further increase the CuSbSe 2 performance. Furthermore, this study also illustrates the advantages of high-throughput experimental methods for fast optimization of the optoelectronic devices based on emerging low-dimensional semiconductor materials.« less

Novel Drift Structures for Silicon and Compound Semiconductor X-Ray and Gamma-Ray Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley E. Patt; Jan S. Iwanczyk

Recently developed silicon- and compound-semiconductor-based drift detector structures have produced excellent performance for charged particles, X rays, and gamma rays and for low-signal visible light detection. The silicon drift detector (SDD) structures that we discuss relate to direct X-ray detectors and scintillation photon detectors coupled with scintillators for gamma rays. Recent designs include several novel features that ensure very low dark current (both bulk silicon dark current and surface dark current) and hence low noise. In addition, application of thin window technology ensures a very high quantum efficiency entrance window on the drift photodetector.

Structure and electrical properties of a one-dimensional polymeric silver thiosaccharinate complex with argentophilic interactions.

PubMed

Dennehy, Mariana; Amo-Ochoa, Pilar; Freire, Eleonora; Suárez, Sebastián; Halac, Emilia; Baggio, Ricardo

2018-02-01

Among the potential applications of coordination polymers, electrical conductivity ranks high in technological interest. We report the synthesis, crystal structure and spectroscopic analysis of an Ag I -thiosaccharinate one-dimensional coordination polymer {systematic name: catena-poly[[[aquatetrakis(μ 3 -1,1-dioxo-1,2-benzisothiazole-3-thiolato-κ 3 N:S 3 :S 3 )tetrasilver(I)]-μ 2 -4,4'-(propane-1,3-diyl)dipyridine-κ 2 N:N'] dimethyl sulfoxide hemisolvate]}, {[Ag 4 (C 7 H 4 NO 2 S 2 ) 4 (C 13 H 14 N 2 )(H 2 O)]·0.5C 2 H 6 OS} n , with the 4,4'-(propane-1,3-diyl)dipyridine ligand acting as a spacer. A relevant feature of the structure is the presence of an unusually short Ag...Ag distance of 2.8306 (9) Å, well within the range of argentophilic interactions, confirmed experimentally as such by a Raman study on the low-frequency spectrum, and corroborated theoretically by an Atoms in Molecules (AIM) analysis of the calculated electron density. Electrical conductivity measurements show that this complex can act as a semiconductor with moderate conductivity.

Defects activated photoluminescence in two-dimensional semiconductors: interplay between bound, charged, and free excitons

PubMed Central

Tongay, Sefaattin; Suh, Joonki; Ataca, Can; Fan, Wen; Luce, Alexander; Kang, Jeong Seuk; Liu, Jonathan; Ko, Changhyun; Raghunathanan, Rajamani; Zhou, Jian; Ogletree, Frank; Li, Jingbo; Grossman, Jeffrey C.; Wu, Junqiao

2013-01-01

Point defects in semiconductors can trap free charge carriers and localize excitons. The interaction between these defects and charge carriers becomes stronger at reduced dimensionalities, and is expected to greatly influence physical properties of the hosting material. We investigated effects of anion vacancies in monolayer transition metal dichalcogenides as two-dimensional (2D) semiconductors where the vacancies density is controlled by α-particle irradiation or thermal-annealing. We found a new, sub-bandgap emission peak as well as increase in overall photoluminescence intensity as a result of the vacancy generation. Interestingly, these effects are absent when measured in vacuum. We conclude that in opposite to conventional wisdom, optical quality at room temperature cannot be used as criteria to assess crystal quality of the 2D semiconductors. Our results not only shed light on defect and exciton physics of 2D semiconductors, but also offer a new route toward tailoring optical properties of 2D semiconductors by defect engineering. PMID:24029823

Effect of a skin-deep surface zone on the formation of a two-dimensional electron gas at a semiconductor surface

NASA Astrophysics Data System (ADS)

Olszowska, Natalia; Lis, Jakub; Ciochon, Piotr; Walczak, Łukasz; Michel, Enrique G.; Kolodziej, Jacek J.

2016-09-01

Two-dimensional electron gases (2DEGs) at surfaces and interfaces of semiconductors are described straightforwardly with a one-dimensional (1D) self-consistent Poisson-Schrödinger scheme. However, their band energies have not been modeled correctly in this way. Using angle-resolved photoelectron spectroscopy we study the band structures of 2DEGs formed at sulfur-passivated surfaces of InAs(001) as a model system. Electronic properties of these surfaces are tuned by changing the S coverage, while keeping a high-quality interface, free of defects and with a constant doping density. In contrast to earlier studies we show that the Poisson-Schrödinger scheme predicts the 2DEG band energies correctly but it is indispensable to take into account the existence of the physical surface. The surface substantially influences the band energies beyond simple electrostatics, by setting nontrivial boundary conditions for 2DEG wave functions.

Thermoelectric properties of low-dimensional clathrates from first principles

NASA Astrophysics Data System (ADS)

Kasinathan, Deepa; Rosner, Helge

2011-03-01

Type-I inorganic clathrates are host-guest structures with the guest atoms trapped in the framework of the host structure. From a thermoelectric point of view, they are interesting because they are semiconductors with adjustable bandgaps. Investigations in the past decade have shown that type-I clathrates X8 Ga 16 Ge 30 (X = Ba, Sr, Eu) may have the unusual property of ``phonon glass-electron crystal'' for good thermoelectric materials. Among the known clathrates, Ba 8 Ga 16 Ge 30 has the highest figure of merit (ZT~1). To enable a more widespread usage of thermoelectric technology power generation and heating/cooling applications, ZT of at least 2-3 is required. Two different research approaches have been proposed for developing next generation thermoelectric materials: one investigating new families of advanced bulk materials, and the other studying low-dimensional materials. In our work, we concentrate on understanding the thermoelectric properties of the nanostructured Ba-based clathrates. We use semi-classical Boltzmann transport equations to calculate the various thermoelectric properties as a function of reduced dimensions. We observe that there exists a delicate balance between the electrical conductivity and the electronic part of the thermal conductivity in reduced dimensions. Insights from these results can directly be used to control particle size in nanostructuring experiments.

One-dimensional polaritons with size-tunable and enhanced coupling strengths in semiconductor nanowires.

PubMed

van Vugt, Lambert K; Piccione, Brian; Cho, Chang-Hee; Nukala, Pavan; Agarwal, Ritesh

2011-06-21

Strong coupling of light with excitons in direct bandgap semiconductors leads to the formation of composite photonic-electronic quasi-particles (polaritons), in which energy oscillates coherently between the photonic and excitonic states with the vacuum Rabi frequency. The light-matter coherence is maintained until the oscillator dephases or the photon escapes. Exciton-polariton formation has enabled the observation of Bose-Einstein condensation in the solid-state, low-threshold polariton lasing and is also useful for terahertz and slow-light applications. However, maintaining coherence for higher carrier concentration and temperature applications still requires increased coupling strengths. Here, we report on size-tunable, exceptionally high exciton-polariton coupling strengths characterized by a vacuum Rabi splitting of up to 200 meV as well as a reduction in group velocity, in surface-passivated, self-assembled semiconductor nanowire cavities. These experiments represent systematic investigations on light-matter coupling in one-dimensional optical nanocavities, demonstrating the ability to engineer light-matter coupling strengths at the nanoscale, even in non-quantum-confined systems, to values much higher than in bulk.

One-dimensional polaritons with size-tunable and enhanced coupling strengths in semiconductor nanowires

PubMed Central

van Vugt, Lambert K.; Piccione, Brian; Cho, Chang-Hee; Nukala, Pavan; Agarwal, Ritesh

2011-01-01

Strong coupling of light with excitons in direct bandgap semiconductors leads to the formation of composite photonic-electronic quasi-particles (polaritons), in which energy oscillates coherently between the photonic and excitonic states with the vacuum Rabi frequency. The light-matter coherence is maintained until the oscillator dephases or the photon escapes. Exciton-polariton formation has enabled the observation of Bose-Einstein condensation in the solid-state, low-threshold polariton lasing and is also useful for terahertz and slow-light applications. However, maintaining coherence for higher carrier concentration and temperature applications still requires increased coupling strengths. Here, we report on size-tunable, exceptionally high exciton-polariton coupling strengths characterized by a vacuum Rabi splitting of up to 200 meV as well as a reduction in group velocity, in surface-passivated, self-assembled semiconductor nanowire cavities. These experiments represent systematic investigations on light-matter coupling in one-dimensional optical nanocavities, demonstrating the ability to engineer light-matter coupling strengths at the nanoscale, even in non-quantum-confined systems, to values much higher than in bulk. PMID:21628582

Canonical Schottky barrier heights of transition metal dichalcogenide monolayers in contact with a metal

NASA Astrophysics Data System (ADS)

Szcześniak, Dominik; Hoehn, Ross D.; Kais, Sabre

2018-05-01

The transition metal dichalcogenide (M X2 , where M =Mo , W and X =S , Se, Te) monolayers are of high interest for semiconducting applications at the nanoscale level; this interest is due to both their direct band gaps and high charge mobilities. In this regard, an in-depth understating of the related Schottky barrier heights, associated with the incorporation of M X2 sheets into novel low-dimensional metal-semiconductor junctions, is of crucial importance. Herein, we generate and provide analysis of the Schottky barrier heights behavior to account for the metal-induced gap states concept as its explanation. In particular, the present investigations concentrate on the estimation of the charge neutrality levels directly by employing the primary theoretical model, i.e., the cell-averaged Green's function formalism combined with the complex band structure technique. The results presented herein place charge neutrality levels in the vicinity of the midgap; this is in agreement with previous reports and analogous to the behavior of three-dimensional semiconductors. The calculated canonical Schottky barrier heights are also found to be in agreement with other computational and experimental values in cases where the difference between electronegativities of the semiconductor and metal contact is small. Moreover, the influence of the spin-orbit effects is herein considered and supports that Schottky barrier heights have metal-induced gap state-derived character, regardless whether spin-orbit coupling interactions are considered. The results presented within this report constitute a direct and vital verification of the importance of metal-induced gap states in explaining the behavior of observed Schottky barrier heights at M X2 -metal junctions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmad, Shahab; Vijaya Prakash, G., E-mail: prakash@physics.iitd.ac.in; Baumberg, Jeremy J.

Room-temperature tunable excitonic photoluminescence is demonstrated in alloy-tuned layered Inorganic-Organic (IO) hybrids, (C{sub 12}H{sub 25}NH{sub 3}){sub 2}PbI{sub 4(1−y)}Br{sub 4y} (y = 0 to 1). These perovskite IO hybrids adopt structures with alternating stacks of low-dimensional inorganic and organic layers, considered to be naturally self-assembled multiple quantum wells. These systems resemble stacked monolayer 2D semiconductors since no interlayer coupling exists. Thin films of IO hybrids exhibit sharp and strong photoluminescence (PL) at room-temperature due to stable excitons formed within the low-dimensional inorganic layers. Systematic variation in the observed exciton PL from 510 nm to 350 nm as the alloy composition is changed, is attributed tomore » the structural readjustment of crystal packing upon increase of the Br content in the Pb-I inorganic network. The energy separation between exciton absorption and PL is attributed to the modified exciton density of states and diffusion of excitons from relatively higher energy states corresponding to bromine rich sites towards the lower energy iodine sites. Apart from compositional fluctuations, these excitons show remarkable reversible flips at temperature-induced phase transitions. All the results are successfully correlated with thermal and structural studies. Such structural engineering flexibility in these hybrids allows selective tuning of desirable exciton properties within suitable operating temperature ranges. Such wide-range PL tunability and reversible exciton switching in these novel IO hybrids paves the way to potential applications in new generation of optoelectronic devices.« less

Decoration of wide bandgap semiconducting materials for enhancing photoelectrochemical efficiency of PEC systems.

NASA Astrophysics Data System (ADS)

Bakranov, N.; Zhabaikhanov, A.; Kudaibergenov, S.; Ibraev, N.

2018-03-01

The production of photoanodes based on wide-band gap materials such as TiO2 is economically viable because of the low cost of synthesis methods. Contrary to economic aspects, wide-band gap semiconductor materials have a significant disadvantage due to low sensitivity to photons of visible light. To increase the photoactive parameters of the material of the electrodes in the visible range, the methods for decorating nanomasses of titanium dioxide by narrow-gap semiconductors are used. One of the most suitable narrow-gap semiconductor materials are CdS and Fe2O3. Controlled deposition of such materials on wide-gap semiconductors allows to regulate both the diffusion time of charge carriers and the band structure of TiO2/Fe2O3 and TiO2/CdS composites. The dimensions of the structure of the photoelectrode material of the cell have a large influence on the characteristics of the photocatalyst created. Thus, in the hematite structures of nanometre dimension, the rate of recombination of charge carriers fades away in comparison with bulk structures. Reducing the size of CdS structures also positively affects the nature of the photocatalytic reaction.

van der Waals epitaxial two-dimensional CdSxSe(1-x) semiconductor alloys with tunable-composition and application to flexible optoelectronics.

PubMed

Xia, Jing; Zhao, Yun-Xuan; Wang, Lei; Li, Xuan-Ze; Gu, Yi-Yi; Cheng, Hua-Qiu; Meng, Xiang-Min

2017-09-21

Despite the substantial progress in the development of two-dimensional (2D) materials from conventional layered crystals, it still remains particularly challenging to produce high-quality 2D non-layered semiconductor alloys which may bring in some unique properties and new functions. In this work, the synthesis of well-oriented 2D non-layered CdS x Se (1-x) semiconductor alloy flakes with tunable compositions and optical properties is established. Structural analysis reveals that the 2D non-layered alloys follow an incommensurate van der Waals epitaxial growth pattern. Photoluminescence measurements show that the 2D alloys have composition-dependent direct bandgaps with the emission peak varying from 1.8 eV to 2.3 eV, coinciding well with the density functional theory calculations. Furthermore, photodetectors based on the CdS x Se (1-x) flakes exhibit a high photoresponsivity of 703 A W -1 with an external quantum efficiency of 1.94 × 10 3 and a response time of 39 ms. Flexible devices fabricated on a thin mica substrate display good mechanical stability upon repeated bending. This work suggests a facile and general method to produce high-quality 2D non-layered semiconductor alloys for next-generation optoelectronic devices.

Exotic ferromagnetism in the two-dimensional quantum material C3N

NASA Astrophysics Data System (ADS)

Huang, Wen-Cheng; Li, Wei; Liu, Xiaosong

2018-04-01

The search for and study of exotic quantum states in novel low-dimensional quantum materials have triggered extensive research in recent years. Here, we systematically study the electronic and magnetic structures in the newly discovered two-dimensional quantum material C3N within the framework of density functional theory. The calculations demonstrate that C3N is an indirect-band semiconductor with an energy gap of 0.38 eV, which is in good agreement with experimental observations. Interestingly, we find van Hove singularities located at energies near the Fermi level, which is half that of graphene. Thus, the Fermi energy easily approaches that of the singularities, driving the system to ferromagnetism, under charge carrier injection, such as electric field gating or hydrogen doping. These findings not only demonstrate that the emergence of magnetism stems from the itinerant electron mechanism rather than the effects of local magnetic impurities, but also open a new avenue to designing field-effect transistor devices for possible realization of an insulator-ferromagnet transition by tuning an external electric field.

Theory of thermionic emission from a two-dimensional conductor and its application to a graphene-semiconductor Schottky junction

NASA Astrophysics Data System (ADS)

Trushin, Maxim

2018-04-01

The standard theory of thermionic emission developed for three-dimensional semiconductors does not apply to two-dimensional materials even for making qualitative predictions because of the vanishing out-of-plane quasiparticle velocity. This study reveals the fundamental origin of the out-of-plane charge carrier motion in a two-dimensional conductor due to the finite quasiparticle lifetime and huge uncertainty of the out-of-plane momentum. The theory is applied to a Schottky junction between graphene and a bulk semiconductor to derive a thermionic constant, which, in contrast to the conventional Richardson constant, is determined by the Schottky barrier height and Fermi level in graphene.

Effect of molecular asymmetry on the charge transport physics of high mobility n-type molecular semiconductors investigated by scanning Kelvin probe microscopy.

PubMed

Hu, Yuanyuan; Berdunov, Nikolai; Di, Chong-an; Nandhakumar, Iris; Zhang, Fengjiao; Gao, Xike; Zhu, Daoben; Sirringhaus, Henning

2014-07-22

We have investigated the influence of the symmetry of the side chain substituents in high-mobility, solution processable n-type molecular semiconductors on the performance of organic field-effect transistors (OFETs). We compare two molecules with the same conjugated core, but either symmetric or asymmetric side chain substituents, and investigate the transport properties and thin film growth mode using scanning Kelvin probe microscopy (SKPM) and atomic force microscopy (AFM). We find that asymmetric side chains can induce a favorable two-dimensional growth mode with a bilayer structure, which enables ultrathin films with a single bilayer to exhibit excellent transport properties, while the symmetric molecules adopt an unfavorable three-dimensional growth mode in which transport in the first monolayer at the interface is severely hindered by high-resistance grain boundaries.

Visible to short wavelength infrared In2Se3-nanoflake photodetector gated by a ferroelectric polymer

NASA Astrophysics Data System (ADS)

Wu, Guangjian; Wang, Xudong; Wang, Peng; Huang, Hai; Chen, Yan; Sun, Shuo; Shen, Hong; Lin, Tie; Wang, Jianlu; Zhang, Shangtao; Bian, Lifeng; Sun, Jinglan; Meng, Xiangjian; Chu, Junhao

2016-09-01

Photodetectors based on two-dimensional (2D) transition-metal dichalcogenides have been studied extensively in recent years. However, the detective spectral ranges, dark current and response time are still unsatisfactory, even under high gate and source-drain bias. In this work, the photodetectors of In2Se3 have been fabricated on a ferroelectric field effect transistor structure. Based on this structure, high performance photodetectors have been achieved with a broad photoresponse spectrum (visible to 1550 nm) and quick response (200 μs). Most importantly, with the intrinsic huge electric field derived from the polarization of ferroelectric polymer (P(VDF-TrFE)) gating, a low dark current of the photodetector can be achieved without additional gate bias. These studies present a crucial step for further practical applications for 2D semiconductors.

Determination of the density of surface states at the semiconductor-insulator interface in a metal-insulator-semiconductor structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gulyamov, G., E-mail: Gulyamov1949@rambler.ru; Sharibaev, N. U.

2011-02-15

The temporal dependence of thermal generation of electrons from occupied surface states at the semiconductor-insulator interface in a metal-insulator-semiconductor structure is studied. It is established that, at low temperatures, the derivative of the probability of depopulation of occupied surface states with respect to energy is represented by the Dirac {delta} function. It is shown that the density of states of a finite number of discrete energy levels under high-temperature measurements manifests itself as a continuous spectrum, whereas this spectrum appears discrete at low temperatures. A method for processing the continuous spectrum of the density of surface states is suggested thatmore » method makes it possible to determine the discrete energy spectrum. The obtained results may be conducive to an increase in resolution of the method of non-stationary spectroscopy of surface states.« less

Coaxial GaAs-AlGaAs core-multishell nanowire lasers with epitaxial gain control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stettner, T., E-mail: Thomas.Stettner@wsi.tum.de, E-mail: Gregor.Koblmueller@wsi.tum.de, E-mail: Jonathan.Finley@wsi.tum.de; Zimmermann, P.; Loitsch, B.

2016-01-04

We demonstrate the growth and single-mode lasing operation of GaAs-AlGaAs core-multishell nanowires (NW) with radial single and multiple GaAs quantum wells (QWs) as active gain media. When subject to optical pumping lasing emission with distinct s-shaped input-output characteristics, linewidth narrowing and emission energies associated with the confined QWs are observed. Comparing the low temperature performance of QW NW laser structures having 7 coaxial QWs with a nominally identical structure having only a single QW shows that the threshold power density reduces several-fold, down to values as low as ∼2.4 kW/cm{sup 2} for the multiple QW NW laser. This confirms that themore » individual radial QWs are electronically weakly coupled and that epitaxial design can be used to optimize the gain characteristics of the devices. Temperature-dependent investigations show that lasing prevails up to 300 K, opening promising new avenues for efficient III–V semiconductor NW lasers with embedded low-dimensional gain media.« less

Syntheses and characterization of one-dimensional alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yohannan, Jinu P.; Vidyasagar, Kanamaluru, E-mail: kvsagar@iitm.ac.in

2015-01-15

Three new isostructural quaternary antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs) have been synthesized by using alkali metal thiosulfate flux and structurally characterized by X-ray diffraction. Their structures contain A{sup +} ions around the [Sb{sub 2}Sn{sub 3}S{sub 10}]{sup 2−} chains, which are built from SbS{sub 3} pyramids, SnS{sub 6} octahedra and SnS{sub 4} tetrahedra. Raman and Mössbauer spectroscopic measurements corroborate the oxidation states and coordination environments of Sb(III) and Sn(IV). All three compounds are wide band gap semiconductors. Potassium compound undergoes partial exchange with strontium, cadmium and lead ions. - Graphical abstract: Syntheses, crystal structure, spectroscopic andmore » partial ion-exchange studies of new one-dimensional alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs) are described. - Highlights: • Syntheses of new alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs). • Wide band gap semiconductors with one-dimensional structure. • Topotactic partial exchange of K{sup +} ions of K{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} with Sr{sup 2+}, Cd{sup 2+} and Pb{sup 2+} ions.« less

Hetero-junction photovoltaic device and method of fabricating the device

DOEpatents

Aytug, Tolga; Christen, David K; Paranthaman, Mariappan Parans; Polat, Ozgur

2014-02-10

A hetero-junction device and fabrication method in which phase-separated n-type and p-type semiconductor pillars define vertically-oriented p-n junctions extending above a substrate. Semiconductor materials are selected for the p-type and n-type pillars that are thermodynamically stable and substantially insoluble in one another. An epitaxial deposition process is employed to form the pillars on a nucleation layer and the mutual insolubility drives phase separation of the materials. During the epitaxial deposition process, the orientation is such that the nucleation layer initiates propagation of vertical columns resulting in a substantially ordered, three-dimensional structure throughout the deposited material. An oxidation state of at least a portion of one of the p-type or the n-type semiconductor materials is altered relative to the other, such that the band-gap energy of the semiconductor materials differ with respect to stoichiometric compositions and the device preferentially absorbs particular selected bands of radiation.

Time-domain measurement of terahertz frequency magnetoplasmon resonances in a two-dimensional electron system by the direct injection of picosecond pulsed currents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Jingbo; Mayorov, Alexander S.; Wood, Christopher D.

2016-02-29

We have investigated terahertz (THz) frequency magnetoplasmon resonances in a two-dimensional electron system through the direct injection of picosecond duration current pulses. The evolution of the time-domain signals was measured as a function of magnetic field, and the results were found to be in agreement with calculations using a mode-matching approach for four modes observed in the frequency range above 0.1 THz. This introduces a generic technique suitable for sampling ultrafast carrier dynamics in low-dimensional semiconductor nanostructures at THz frequencies.

Low temperature anomaly of light stimulated magnetization and heat capacity of the 1D diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Geffe, Chernet Amente

2018-03-01

This article reports magnetization and specific heat capacity anomalies in one dimensional diluted magnetic semiconductors observed at very low temperatures. Based on quantum field theory double time temperature dependent Green function technique is employed to evaluate magnon dispersion and the time correlation function. It is understood that magnon-photon coupling and magnetic impurity concentration controls both, such that near absolute temperature magnetization is nearly zero and abruptly increase to saturation level with decreasing magnon-photon coupling strength. We also found out dropping of magnetic specific heat capacity as a result of increase in magnetic impurity concentration x, perhaps because of inter-band disorder that would suppress the enhancement of density of spin waves.

Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Xiaoyang

2014-12-10

The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering. Organic semiconductors are emerging as viable materials for low-cost electronics and optoelectronics, such as organic photovoltaics (OPV), organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). Despite extensive studies spanning many decades, a clear understanding of the nature of charge carriers in organic semiconductors is still lacking. It is generally appreciated that polaron formation and charge carrier trapping are two hallmarks associatedmore » with electrical transport in organic semiconductors; the former results from the low dielectric constants and weak intermolecular electronic overlap while the latter can be attributed to the prevalence of structural disorder. These properties have lead to the common observation of low charge carrier mobilities, e.g., in the range of 10-5 - 10-3 cm2/Vs, particularly at low carrier concentrations. However, there is also growing evidence that charge carrier mobility approaching those of inorganic semiconductors and metals can exist in some crystalline organic semiconductors, such as pentacene, tetracene and rubrene. A particularly striking example is single crystal rubrene (Figure 1), in which hole mobilities well above 10 cm2/Vs have been observed in OFETs operating at room temperature. Temperature dependent transport and spectroscopic measurements both revealed evidence of free carriers in rubrene. Outstanding questions are: what are the structural features and physical properties that make rubrene so unique? How do we establish fundamental design principles for the development of other organic semiconductors of high mobility? These questions are critically important but not comprehensive, as the nature of charge carriers is known to evolve as the carrier concentration increases, due to the presence of intrinsic disorder in organic semiconductors. Thus, a complementary question is: how does the nature of charge transport change as a function of carrier concentration?« less

Vapor-solid growth of one-dimensional layer-structured gallium sulfide nanostructures.

PubMed

Shen, Guozhen; Chen, Di; Chen, Po-Chiang; Zhou, Chongwu

2009-05-26

Gallium sulfide (GaS) is a wide direct bandgap semiconductor with uniform layered structure used in photoelectric devices, electrical sensors, and nonlinear optical applications. We report here the controlled synthesis of various high-quality one-dimensional GaS nanostructures (thin nanowires, nanobelts, and zigzag nanobelts) as well as other kinds of GaS products (microbelts, hexagonal microplates, and GaS/Ga(2)O(3) heterostructured nanobelts) via a simple vapor-solid method. The morphology and structures of the products can be easily controlled by substrate temperature and evaporation source. Optical properties of GaS thin nanowires and nanobelts were investigated and both show an emission band centered at 580 nm.

Exact solution of three-dimensional transport problems using one-dimensional models. [in semiconductor devices

NASA Technical Reports Server (NTRS)

Misiakos, K.; Lindholm, F. A.

1986-01-01

Several parameters of certain three-dimensional semiconductor devices including diodes, transistors, and solar cells can be determined without solving the actual boundary-value problem. The recombination current, transit time, and open-circuit voltage of planar diodes are emphasized here. The resulting analytical expressions enable determination of the surface recombination velocity of shallow planar diodes. The method involves introducing corresponding one-dimensional models having the same values of these parameters.

Crystal Growth and Characterization of the Narrow-Band-Gap Semiconductors OsPn 2 (Pn = P, As, Sb)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bugaris, Daniel E.; Malliakas, Christos D.; Shoemaker, Daniel P.

2014-09-15

Using metal fluxes, crystals of the binary osmium dipnictides OsPn(2) (Pn = P, As, Sb) have been grown for the first time. Single-crystal X-ray diffraction confirms that these compounds crystallize in the marcasite structure type with orthorhombic space group Pnnm. The structure is a three-dimensional framework of corner- and edge-sharing OsPn(6) octahedra, as well as [Pn(2)(-4)] anions. Raman spectroscopy shows the presence of PP single bonds, consistent with the presence of [Pn(2)(-4)] anions and formally Os4+ cations. Optical-band-gap and high-temperature electrical resistivity measurements indicate that these materials are narrow-band-gap semiconductors. The experimentally determined Seebeck coefficients reveal that nominally undoped OsP2more » and OsSb2 are n-type semiconductors, whereas OsAs2 is p-type. Electronic band structure using density functional theory calculations shows that these compounds are indirect narrow-band-gap semiconductors. The bonding p orbitals associated with the Pn(2) dimer are below the Fermi energy, and the corresponding antibonding states are above, consistent with a PnPn single bond. Thermopower calculations using Boltzmann transport theory and constant relaxation time approximation show that these materials are potentially good thermoelectrics, in agreement with experiment.« less

Electronic Structure and I- V Characteristics of InSe Nanoribbons

NASA Astrophysics Data System (ADS)

Yao, A.-Long; Wang, Xue-Feng; Liu, Yu-Shen; Sun, Ya-Na

2018-04-01

We have studied the electronic structure and the current-voltage ( I-V) characteristics of one-dimensional InSe nanoribbons using the density functional theory combined with the nonequilibrium Green's function method. Nanoribbons having bare or H-passivated edges of types zigzag (Z), Klein (K), and armchair (A) are taken into account. Edge states are found to play an important role in determining their electronic properties. Edges Z and K are usually metallic in wide nanoribbons as well as their hydrogenated counterparts. Transition from semiconductor to metal is observed in hydrogenated nanoribbons HZZH as their width increases, due to the strong width dependence of energy difference between left and right edge states. Nevertheless, electronic structures of other nanoribbons vary with the width in a very limited scale. The I-V characteristics of bare nanoribbons ZZ and KK show strong negative differential resistance, due to spatial mismatch of wave functions in energy bands around the Fermi energy. Spin polarization in these nanoribbons is also predicted. In contrast, bare nanoribbons AA and their hydrogenated counterparts HAAH are semiconductors. The band gaps of nanoribbons AA (HAAH) are narrower (wider) than that of two-dimensional InSe monolayer and increase (decrease) with the nanoribbon width.

Semiconductor Metal-Organic Frameworks: Future Low-Bandgap Materials.

PubMed

Usman, Muhammad; Mendiratta, Shruti; Lu, Kuang-Lieh

2017-02-01

Metal-organic frameworks (MOFs) with low density, high porosity, and easy tunability of functionality and structural properties, represent potential candidates for use as semiconductor materials. The rapid development of the semiconductor industry and the continuous miniaturization of feature sizes of integrated circuits toward the nanometer (nm) scale require novel semiconductor materials instead of traditional materials like silicon, germanium, and gallium arsenide etc. MOFs with advantageous properties of both the inorganic and the organic components promise to serve as the next generation of semiconductor materials for the microelectronics industry with the potential to be extremely stable, cheap, and mechanically flexible. Here, a perspective of recent research is provided, regarding the semiconducting properties of MOFs, bandgap studies, and their potential in microelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method of Forming Three-Dimensional Semiconductors Structures

NASA Technical Reports Server (NTRS)

Fathauer, Robert W. (Inventor)

2002-01-01

Silicon and metal are coevaporated onto a silicon substrate in a molecular beam epitaxy system with a larger than stoichiometric amount of silicon so as to epitaxially grow columns of metal silicide embedded in a matrix of single crystal, epitaxially grown silicon. Higher substrate temperatures and lower deposition rates yield larger columns that are farther apart while more silicon produces smaller columns. Column shapes and locations are selected by seeding the substrate with metal silicide starting regions. A variety of 3-dimensional, exemplary electronic devices are disclosed.

Observation of Structure of Surfaces and Interfaces by Synchrotron X-ray Diffraction: Atomic-Scale Imaging and Time-Resolved Measurements

NASA Astrophysics Data System (ADS)

Wakabayashi, Yusuke; Shirasawa, Tetsuroh; Voegeli, Wolfgang; Takahashi, Toshio

2018-06-01

The recent developments in synchrotron optics, X-ray detectors, and data analysis algorithms have enhanced the capability of the surface X-ray diffraction technique. This technique has been used to clarify the atomic arrangement around surfaces in a non-contact and nondestructive manner. An overview of surface X-ray diffraction, from the historical development to recent topics, is presented. In the early stage of this technique, surface reconstructions of simple semiconductors or metals were studied. Currently, the surface or interface structures of complicated functional materials are examined with sub-Å resolution. As examples, the surface structure determination of organic semiconductors and of a one-dimensional structure on silicon are presented. A new frontier is time-resolved interfacial structure analysis. A recent observation of the structure and dynamics of the electric double layer of ionic liquids, and an investigation of the structural evolution in the wettability transition on a TiO2 surface that utilizes a newly designed time-resolved surface diffractometer, are presented.

High efficiency and non-Richardson thermionics in three dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Huang, Sunchao; Sanderson, Matthew; Zhang, Yan; Zhang, Chao

2017-10-01

Three dimensional (3D) topological materials have a linear energy dispersion and exhibit many electronic properties superior to conventional materials such as fast response times, high mobility, and chiral transport. In this work, we demonstrate that 3D Dirac materials also have advantages over conventional semiconductors and graphene in thermionic applications. The low emission current suffered in graphene due to the vanishing density of states is enhanced by an increased group velocity in 3D Dirac materials. Furthermore, the thermal energy carried by electrons in 3D Dirac materials is twice of that in conventional materials with a parabolic electron energy dispersion. As a result, 3D Dirac materials have the best thermal efficiency or coefficient of performance when compared to conventional semiconductors and graphene. The generalized Richardson-Dushman law in 3D Dirac materials is derived. The law exhibits the interplay of the reduced density of states and enhanced emission velocity.

Bipolar resistive switching in metal-insulator-semiconductor nanostructures based on silicon nitride and silicon oxide

NASA Astrophysics Data System (ADS)

Koryazhkina, M. N.; Tikhov, S. V.; Mikhaylov, A. N.; Belov, A. I.; Korolev, D. S.; Antonov, I. N.; Karzanov, V. V.; Gorshkov, O. N.; Tetelbaum, D. I.; Karakolis, P.; Dimitrakis, P.

2018-03-01

Bipolar resistive switching in metal-insulator-semiconductor (MIS) capacitor-like structures with an inert Au top electrode and a Si3N4 insulator nanolayer (6 nm thick) has been observed. The effect of a highly doped n +-Si substrate and a SiO2 interlayer (2 nm) is revealed in the changes in the semiconductor space charge region and small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of the semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

Theoretical predictions on the electronic structure and charge carrier mobility in 2D Phosphorus sheets

PubMed Central

Xiao, Jin; Long, Mengqiu; Zhang, Xiaojiao; Ouyang, Jun; Xu, Hui; Gao, Yongli

2015-01-01

We have investigated the electronic structure and carrier mobility of four types of phosphorous monolayer sheet (α-P, β-P,γ-P and δ-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 × 105 cm2V−1s−1, which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, α-P, γ-P and δ-P sheets can be considered as n-type semiconductors, and β-P sheet can be considered as a p-type semiconductor. Our results suggest that phosphorous monolayer sheets can be considered as a new type of two dimensional materials for applications in optoelectronics and nanoelectronic devices. PMID:26035176

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

PubMed Central

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; Lupini, Andrew R.; Lee, Jaekwang; Basile, Leonardo; Boulesbaa, Abdelaziz; Rouleau, Christopher M.; Puretzky, Alexander A.; Ivanov, Ilia N.; Xiao, Kai; Yoon, Mina; Geohegan, David B.

2015-01-01

The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices. PMID:26198727

Origin of poor doping efficiency in solution processed organic semiconductors.

PubMed

Jha, Ajay; Duan, Hong-Guang; Tiwari, Vandana; Thorwart, Michael; Miller, R J Dwayne

2018-05-21

Doping is an extremely important process where intentional insertion of impurities in semiconductors controls their electronic properties. In organic semiconductors, one of the convenient, but inefficient, ways of doping is the spin casting of a precursor mixture of components in solution, followed by solvent evaporation. Active control over this process holds the key to significant improvements over current poor doping efficiencies. Yet, an optimized control can only come from a detailed understanding of electronic interactions responsible for the low doping efficiencies. Here, we use two-dimensional nonlinear optical spectroscopy to examine these interactions in the course of the doping process by probing the solution mixture of doped organic semiconductors. A dopant accepts an electron from the semiconductor and the two ions form a duplex of interacting charges known as ion-pair complexes. Well-resolved off-diagonal peaks in the two-dimensional spectra clearly demonstrate the electronic connectivity among the ions in solution. This electronic interaction represents a well resolved electrostatically bound state, as opposed to a random distribution of ions. We developed a theoretical model to recover the experimental data, which reveals an unexpectedly strong electronic coupling of ∼250 cm -1 with an intermolecular distance of ∼4.5 Å between ions in solution, which is approximately the expected distance in processed films. The fact that this relationship persists from solution to the processed film gives direct evidence that Coulomb interactions are retained from the precursor solution to the processed films. This memory effect renders the charge carriers equally bound also in the film and, hence, results in poor doping efficiencies. This new insight will help pave the way towards rational tailoring of the electronic interactions to improve doping efficiencies in processed organic semiconductor thin films.

Rietveld-refinement and optical study of the Fe doped ZnO thin film by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Kumar, Arun; Dhiman, Pooja; Singh, M.

2017-05-01

Fe Doped ZnO Dilute Magnetic Semiconductor thin film prepared by RF magnetron sputtering on glass substrate and Influence of 3% Fe-doping on structural and Optical properties has been studied. The Rietveld-refinement analysis shows that Fe doping has a significant effect on crystalline structure, grain size and strain in the thin film. Two dimensional and three-dimensional atom probe tomography of the thin film shows that Fe ions are randomly distributed which is supported by Xray Diffraction (XRD). Fe-doping is found to effectively modify the band gap energy up to 3.5 eV.

Metal-Insulator-Semiconductor Diode Consisting of Two-Dimensional Nanomaterials.

PubMed

Jeong, Hyun; Oh, Hye Min; Bang, Seungho; Jeong, Hyeon Jun; An, Sung-Jin; Han, Gang Hee; Kim, Hyun; Yun, Seok Joon; Kim, Ki Kang; Park, Jin Cheol; Lee, Young Hee; Lerondel, Gilles; Jeong, Mun Seok

2016-03-09

We present a novel metal-insulator-semiconductor (MIS) diode consisting of graphene, hexagonal BN, and monolayer MoS2 for application in ultrathin nanoelectronics. The MIS heterojunction structure was fabricated by vertically stacking layered materials using a simple wet chemical transfer method. The stacking of each layer was confirmed by confocal scanning Raman spectroscopy and device performance was evaluated using current versus voltage (I-V) and photocurrent measurements. We clearly observed better current rectification and much higher current flow in the MIS diode than in the p-n junction and the metal-semiconductor diodes made of layered materials. The I-V characteristic curve of the MIS diode indicates that current flows mainly across interfaces as a result of carrier tunneling. Moreover, we observed considerably high photocurrent from the MIS diode under visible light illumination.

Engineering light emission of two-dimensional materials in both the weak and strong coupling regimes

NASA Astrophysics Data System (ADS)

Brotons-Gisbert, Mauro; Martínez-Pastor, Juan P.; Ballesteros, Guillem C.; Gerardot, Brian D.; Sánchez-Royo, Juan F.

2018-01-01

Two-dimensional (2D) materials have promising applications in optoelectronics, photonics, and quantum technologies. However, their intrinsically low light absorption limits their performance, and potential devices must be accurately engineered for optimal operation. Here, we apply a transfer matrix-based source-term method to optimize light absorption and emission in 2D materials and related devices in weak and strong coupling regimes. The implemented analytical model accurately accounts for experimental results reported for representative 2D materials such as graphene and MoS2. The model has been extended to propose structures to optimize light emission by exciton recombination in MoS2 single layers, light extraction from arbitrarily oriented dipole monolayers, and single-photon emission in 2D materials. Also, it has been successfully applied to retrieve exciton-cavity interaction parameters from MoS2 microcavity experiments. The present model appears as a powerful and versatile tool for the design of new optoelectronic devices based on 2D semiconductors such as quantum light sources and polariton lasers.

Spectra, current flow, and wave-function morphology in a model PT -symmetric quantum dot with external interactions

NASA Astrophysics Data System (ADS)

Tellander, Felix; Berggren, Karl-Fredrik

2017-04-01

In this paper we use numerical simulations to study a two-dimensional (2D) quantum dot (cavity) with two leads for passing currents (electrons, photons, etc.) through the system. By introducing an imaginary potential in each lead the system is made symmetric under parity-time inversion (PT symmetric). This system is experimentally realizable in the form of, e.g., quantum dots in low-dimensional semiconductors, optical and electromagnetic cavities, and other classical wave analogs. The computational model introduced here for studying spectra, exceptional points (EPs), wave-function symmetries and morphology, and current flow includes thousands of interacting states. This supplements previous analytic studies of few interacting states by providing more detail and higher resolution. The Hamiltonian describing the system is non-Hermitian; thus, the eigenvalues are, in general, complex. The structure of the wave functions and probability current densities are studied in detail at and in between EPs. The statistics for EPs is evaluated, and reasons for a gradual dynamical crossover are identified.

Reconfigurable exciton-plasmon interconversion for nanophotonic circuits

PubMed Central

Lee, Hyun Seok; Luong, Dinh Hoa; Kim, Min Su; Jin, Youngjo; Kim, Hyun; Yun, Seokjoon; Lee, Young Hee

2016-01-01

The recent challenges for improving the operation speed of nanoelectronics have motivated research on manipulating light in on-chip integrated circuits. Hybrid plasmonic waveguides with low-dimensional semiconductors, including quantum dots and quantum wells, are a promising platform for realizing sub-diffraction limited optical components. Meanwhile, two-dimensional transition metal dichalcogenides (TMDs) have received broad interest in optoelectronics owing to tightly bound excitons at room temperature, strong light-matter and exciton-plasmon interactions, available top-down wafer-scale integration, and band-gap tunability. Here, we demonstrate principal functionalities for on-chip optical communications via reconfigurable exciton-plasmon interconversions in ∼200-nm-diameter Ag-nanowires overlapping onto TMD transistors. By varying device configurations for each operation purpose, three active components for optical communications are realized: field-effect exciton transistors with a channel length of ∼32 μm, field-effect exciton multiplexers transmitting multiple signals through a single NW and electrical detectors of propagating plasmons with a high On/Off ratio of∼190. Our results illustrate the unique merits of two-dimensional semiconductors for constructing reconfigurable device architectures in integrated nanophotonic circuits. PMID:27892463

Exciton-plasmon coupling in two-dimensional plexitonic nano grating

NASA Astrophysics Data System (ADS)

Asgari, N.; Hamidi, S. M.

2018-07-01

The proximity of metal and semiconductor nanostructures leads to the emergence of new optical features for many tunable applications, which affects the electromagnetic modes in metallic nanostructure and electronic states in semiconductor nanostructure in nanometer scales. Thus, it will create some changes in the transition matrix elements and the absorption and emission properties. Therefore, absorption and emission properties can be designed and controlled by exciton-plasmon interaction. In the present study, Rhodamine-B and 6G were used as organic dyes in Polyvinylpyrrolidone as host medium and two-dimensional crystal as plasmonic ones. To this aim, Nano imprint lithography was used to produce two dimensional crystals and its deposit gold was utilized to harvest plasmonic mold in the proximity of excitonic media. Then, the dispersion relation was measured and the polar diagram was plotted for different coupling regime. Based on the results, this system has a poor capability for overcoming the difficulties of obtaining strong coupling although different figures of merit were observed for increasing coupling strength, which is very useful for designing and constructing new generation of plexitonic structures.

On-chip micro-power: three-dimensional structures for micro-batteries and micro-supercapacitors

NASA Astrophysics Data System (ADS)

Beidaghi, Majid; Wang, Chunlei

2010-04-01

With the miniaturization of portable electronic devices, there is a demand for micro-power source which can be integrated on the semiconductor chips. Various micro-batteries have been developed in recent years to generate or store the energy that is needed by microsystems. Micro-supercapacitors are also developed recently to couple with microbatteries and energy harvesting microsystems and provide the peak power. Increasing the capacity per footprint area of micro-batteries and micro-supercapacitors is a great challenge. One promising route is the manufacturing of three dimensional (3D) structures for these micro-devices. In this paper, the recent advances in fabrication of 3D structure for micro-batteries and micro-supercapacitors are briefly reviewed.

Design of a nano-layered tunable optical filter

NASA Astrophysics Data System (ADS)

Banerjee, A.; Awasthi, S. K.; Malaviya, U.; Ojha, S. P.

2006-12-01

A novel theory to design tunable band pass filters using one-dimensional nano-photonic structures is proposed. Periodic structures consisting of different dielectrics and semiconductor materials are considered. A detailed mathematical analysis is presented to predict allowed and forbidden bands of wavelengths with variation of angle of incidence and lattice parameters. It is possible to get desired ranges of the electromagnetic spectrum filtered with this structure by changing the incidence angle of light and/or changing the value of the lattice parameters.

High efficiency, low cost, thin film silicon solar cell design and method for making

DOEpatents

Sopori, Bhushan L.

2001-01-01

A semiconductor device having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer.

High efficiency low cost thin film silicon solar cell design and method for making

DOEpatents

Sopori, Bhushan L.

1999-01-01

A semiconductor device having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer.

Electronic, Optical, and Thermal Properties of Reduced-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Huang, Shouting

Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell N-Ws. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphene-like system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE PAGES

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

2017-04-14

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Wholly Aromatic Ether-Imides as n-Type Semiconductors

NASA Technical Reports Server (NTRS)

Weiser, Erik; St. Clair, Terry L.; Dingemans, Theo J.; Samulski, Edward T.; Irene, Gene

2006-01-01

Some wholly aromatic ether-imides consisting of rod-shaped, relatively-low-mass molecules that can form liquid crystals have been investigated for potential utility as electron-donor-type (ntype) organic semiconductors. It is envisioned that after further research to improve understanding of their physical and chemical properties, compounds of this type would be used to make thin film semiconductor devices (e.g., photovoltaic cells and field-effect transistors) on flexible electronic-circuit substrates. This investigation was inspired by several prior developments: Poly(ether-imides) [PEIs] are a class of engineering plastics that have been used extensively in the form of films in a variety of electronic applications, including insulating layers, circuit boards, and low-permittivity coatings. Wholly aromatic PEIs containing naphthalene and perylene moieties have been shown to be useful as electrochromic polymers. More recently, low-molecular-weight imides comprising naphthalene-based molecules with terminal fluorinated tails were shown to be useful as n-type organic semiconductors in such devices as field-effect transistors and Schottky diodes. Poly(etherimide)s as structural resins have been extensively investigated at NASA Langley Research Center for over 30 years. More recently, the need for multi-functional materials has become increasingly important. This n-type semiconductor illustrates the scope of current work towards new families of PEIs that not only can be used as structural resins for carbon-fiber reinforced composites, but also can function as sensors. Such a multi-functional material would permit so-called in-situ health monitoring of composite structures during service. The work presented here demonstrates that parts of the PEI backbone can be used as an n-type semiconductor with such materials being sensitive to damage, temperature, stress, and pressure. In the near future, multi-functional or "smart" composite structures are envisioned to be able to communicate such important parameters to the flight crew and provide vital information with respect to the operational status of their aircraft.

Directional interlayer spin-valley transfer in two-dimensional heterostructures

DOE PAGES

Schaibley, John R.; Rivera, Pasqual; Yu, Hongyi; ...

2016-12-14

Van der Waals heterostructures formed by two different monolayer semiconductors have emerged as a promising platform for new optoelectronic and spin/valleytronic applications. In addition to its atomically thin nature, a two-dimensional semiconductor heterostructure is distinct from its three-dimensional counterparts due to the unique coupled spin-valley physics of its constituent monolayers. In this paper, we report the direct observation that an optically generated spin-valley polarization in one monolayer can be transferred between layers of a two-dimensional MoSe 2–WSe 2 heterostructure. Using non-degenerate optical circular dichroism spectroscopy, we show that charge transfer between two monolayers conserves spin-valley polarization and is only weaklymore » dependent on the twist angle between layers. Finally, our work points to a new spin-valley pumping scheme in nanoscale devices, provides a fundamental understanding of spin-valley transfer across the two-dimensional interface, and shows the potential use of two-dimensional semiconductors as a spin-valley generator in two-dimensional spin/valleytronic devices for storing and processing information.« less

Optical Properties and Wave Propagation in Semiconductor-Based Two-Dimensional Photonic Crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agio, Mario

2002-12-31

This work is a theoretical investigation on the physical properties of semiconductor-based two-dimensional photonic crystals, in particular for what concerns systems embedded in planar dielectric waveguides (GaAs/AlGaAs, GaInAsP/InP heterostructures, and self-standing membranes) or based on macro-porous silicon. The photonic-band structure of photonic crystals and photonic-crystal slabs is numerically computed and the associated light-line problem is discussed, which points to the issue of intrinsic out-of-lane diffraction losses for the photonic bands lying above the light line. The photonic states are then classified by the group theory formalism: each mode is related to an irreducible representation of the corresponding small point group.more » The optical properties are investigated by means of the scattering matrix method, which numerically implements a variable-angle-reflectance experiment; comparison with experiments is also provided. The analysis of surface reflectance proves the existence of selection rules for coupling an external wave to a certain photonic mode. Such rules can be directly derived from symmetry considerations. Lastly, the control of wave propagation in weak-index contrast photonic-crystal slabs is tackled in view of designing building blocks for photonic integrated circuits. The proposed designs are found to comply with the major requirements of low-loss propagation, high and single-mode transmission. These notions are then collected to model a photonic-crystal combiner for an integrated multi-wavelength-source laser.« less

Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

DOEpatents

Findikoglu, Alp T [Los Alamos, NM; Jia, Quanxi [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM; Matias, Vladimir [Santa Fe, NM; Choi, Woong [Los Alamos, NM

2009-10-27

A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

Release strategies for making transferable semiconductor structures, devices and device components

DOEpatents

Rogers, John A; Nuzzo, Ralph G; Meitl, Matthew; Ko, Heung Cho; Yoon, Jongseung; Menard, Etienne; Baca, Alfred J

2014-11-25

Provided are methods for making a device or device component by providing a multilayer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

Release strategies for making transferable semiconductor structures, devices and device components

DOEpatents

Rogers, John A [Champaign, IL; Nuzzo, Ralph G [Champaign, IL; Meitl, Matthew [Raleigh, NC; Ko, Heung Cho [Urbana, IL; Yoon, Jongseung [Urbana, IL; Menard, Etienne [Durham, NC; Baca, Alfred J [Urbana, IL

2011-04-26

Provided are methods for making a device or device component by providing a multilayer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

Release strategies for making transferable semiconductor structures, devices and device components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogers, John A.; Nuzzo, Ralph G.; Meitl, Matthew

2016-05-24

Provided are methods for making a device or device component by providing a multi layer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

Fabrication and independent control of patterned polymer gate for a few-layer WSe{sub 2} field-effect transistor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Sung Ju; Park, Min; Kang, Hojin

We report the fabrication of a patterned polymer electrolyte for a two-dimensional (2D) semiconductor, few-layer tungsten diselenide (WSe{sub 2}) field-effect transistor (FET). We expose an electron-beam in a desirable region to form the patterned structure. The WSe{sub 2} FET acts as a p-type semiconductor in both bare and polymer-covered devices. We observe a highly efficient gating effect in the polymer-patterned device with independent gate control. The patterned polymer gate operates successfully in a molybdenum disulfide (MoS{sub 2}) FET, indicating the potential for general applications to 2D semiconductors. The results of this study can contribute to large-scale integration and better flexibilitymore » in transition metal dichalcogenide (TMD)-based electronics.« less

Characteristics of strain-sensitive photonic crystal cavities in a flexible substrate.

PubMed

No, You-Shin; Choi, Jae-Hyuck; Kim, Kyoung-Ho; Park, Hong-Gyu

2016-11-14

High-index semiconductor photonic crystal (PhC) cavities in a flexible substrate support strong and tunable optical resonances that can be used for highly sensitive and spatially localized detection of mechanical deformations in physical systems. Here, we report theoretical studies and fundamental understandings of resonant behavior of an optical mode excited in strain-sensitive rod-type PhC cavities consisting of high-index dielectric nanorods embedded in a low-index flexible polymer substrate. Using the three-dimensional finite-difference time-domain simulation method, we calculated two-dimensional transverse-electric-like photonic band diagrams and the three-dimensional dispersion surfaces near the first Γ-point band edge of unidirectionally strained PhCs. A broken rotational symmetry in the PhCs modifies the photonic band structures and results in the asymmetric distributions and different levels of changes in normalized frequencies near the first Γ-point band edge in the reciprocal space, which consequently reveals strain-dependent directional optical losses and selected emission patterns. The calculated electric fields, resonant wavelengths, and quality factors of the band-edge modes in the strained PhCs show an excellent agreement with the results of qualitative analysis of modified dispersion surfaces. Furthermore, polarization-resolved time-averaged Poynting vectors exhibit characteristic dipole-like emission patterns with preferentially selected linear polarizations, originating from the asymmetric band structures in the strained PhCs.

Optical response from lenslike semiconductor nipple arrays

NASA Astrophysics Data System (ADS)

Wu, H.-M.; Lai, C.-M.; Peng, L.-H.

2008-11-01

The authors reported the use of recessive size reduction in self-assembled polystyrene sphere mask with anisotropic etching to form lenslike nipple arrays onto the surface of silicon and gallium nitride. These devices are shown to exhibit a filling factor near to an ideal close-packed condition and paraboloidlike etch profile with slope increased proportionally to the device aspect ratio. Specular reflectivity of less than 3% was observed over the visible spectral range for the 0.35-μm-period nipple-lens arrays. Using two-dimensional rigorous coupled-wave analysis, the latter phenomenon can be ascribed to a gradual index matching mechanism accessed by a high surface-coverage semiconductor nipple array structure.

Computer modeling of inversion layer MOS solar cells and arrays

NASA Technical Reports Server (NTRS)

Ho, Fat Duen

1991-01-01

A two dimensional numerical model of the inversion layer metal insulator semiconductor (IL/MIS) solar cell is proposed by using the finite element method. The two-dimensional current flow in the device is taken into account in this model. The electrostatic potential distribution, the electron concentration distribution, and the hole concentration distribution for different terminal voltages are simulated. The results of simple calculation are presented. The existing problems for this model are addressed. Future work is proposed. The MIS structures are studied and some of the results are reported.

One-dimensional ZnO nanostructures.

PubMed

Jayadevan, K P; Tseng, T Y

2012-06-01

The wide-gap semiconductor ZnO with nanostructures such as nanoparticle, nanorod, nanowire, nanobelt, nanotube has high potential for a variety of applications. This article reviews the fundamentals of one-dimensional ZnO nanostructures, including processing, structure, property, application and their processing-microstructure-property correlation. Various fabrication methods of the ZnO nanostructures including vapor-liquid-solid process, vapor-solid growth, solution growth, solvothermal growth, template-assisted growth and self-assembly are introduced. The characterization and properties of the ZnO nanostructures are described. The possible applications of these nanostructures are also discussed.

Highly directional thermal emitter

DOEpatents

Ribaudo, Troy; Shaner, Eric A; Davids, Paul; Peters, David W

2015-03-24

A highly directional thermal emitter device comprises a two-dimensional periodic array of heavily doped semiconductor structures on a surface of a substrate. The array provides a highly directional thermal emission at a peak wavelength between 3 and 15 microns when the array is heated. For example, highly doped silicon (HDSi) with a plasma frequency in the mid-wave infrared was used to fabricate nearly perfect absorbing two-dimensional gratings structures that function as highly directional thermal radiators. The absorption and emission characteristics of the HDSi devices possessed a high degree of angular dependence for infrared absorption in the 10-12 micron range, while maintaining high reflectivity of solar radiation (.about.64%) at large incidence angles.

Ordered nanoparticle arrays formed on engineered chaperonin protein templates

NASA Technical Reports Server (NTRS)

McMillan, R. Andrew; Paavola, Chad D.; Howard, Jeanie; Chan, Suzanne L.; Zaluzec, Nestor J.; Trent, Jonathan D.

2002-01-01

Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Some proteins, for example, have been used to form ordered two-dimensional arrays. Here, we fabricated nanoscale ordered arrays of metal and semiconductor quantum dots by binding preformed nanoparticles onto crystalline protein templates made from genetically engineered hollow double-ring structures called chaperonins. Using structural information as a guide, a thermostable recombinant chaperonin subunit was modified to assemble into chaperonins with either 3 nm or 9 nm apical pores surrounded by chemically reactive thiols. These engineered chaperonins were crystallized into two-dimensional templates up to 20 microm in diameter. The periodic solvent-exposed thiols within these crystalline templates were used to size-selectively bind and organize either gold (1.4, 5 or 10nm) or CdSe-ZnS semiconductor (4.5 nm) quantum dots into arrays. The order within the arrays was defined by the lattice of the underlying protein crystal. By combining the self-assembling properties of chaperonins with mutations guided by structural modelling, we demonstrate that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.

Doping of two-dimensional MoS2 by high energy ion implantation

NASA Astrophysics Data System (ADS)

Xu, Kang; Zhao, Yuda; Lin, Ziyuan; Long, Yan; Wang, Yi; Chan, Mansun; Chai, Yang

2017-12-01

Two-dimensional (2D) materials have been demonstrated to be promising candidates for next generation electronic circuits. Analogues to conventional Si-based semiconductors, p- and n-doping of 2D materials are essential for building complementary circuits. Controllable and effective doping strategies require large tunability of the doping level and negligible structural damage to ultrathin 2D materials. In this work, we demonstrate a doping method utilizing a conventional high-energy ion-implantation machine. Before the implantation, a Polymethylmethacrylate (PMMA) protective layer is used to decelerate the dopant ions and minimize the structural damage to MoS2, thus aggregating the dopants inside MoS2 flakes. By optimizing the implantation energy and fluence, phosphorus dopants are incorporated into MoS2 flakes. Our Raman and high-resolution transmission electron microscopy (HRTEM) results show that only negligibly structural damage is introduced to the MoS2 lattice during the implantation. P-doping effect by the incorporation of p+ is demonstrated by Photoluminescence (PL) and electrical characterizations. Thin PMMA protection layer leads to large kinetic damage but also a more significant doping effect. Also, MoS2 with large thickness shows less kinetic damage. This doping method makes use of existing infrastructures in the semiconductor industry and can be extended to other 2D materials and dopant species as well.

Electronic part of the optical correlation function at finite temperature: the S-matrix expansion

NASA Astrophysics Data System (ADS)

Tavares, M.; Marques, G. E.; Tejedor, C.

1998-12-01

We present an extension to finite temperature of the Mahan-Nozières-De Dominicis framework to obtain the electronic part of the current-current correlation function. Its Fourier transform gives the absorption and emission spectra of doped low-dimensional semiconductors. We show the meaning of the new finite-temperature contributions characterizing the electronic part.

Metallic Junction Thermoelectric Device Simulations

NASA Technical Reports Server (NTRS)

Duzik, Adam J.; Choi, Sang H.

2017-01-01

Thermoelectric junctions made of semiconductors have existed in radioisotope thermoelectric generators (RTG) for deep space missions, but are currently being adapted for terrestrial energy harvesting. Unfortunately, these devices are inefficient, operating at only 7% efficiency. This low efficiency has driven efforts to make high-figure-of-merit thermoelectric devices, which require a high electrical conductivity but a low thermal conductivity, a combination that is difficult to achieve. Lowered thermal conductivity has increased efficiency, but at the cost of power output. An alternative setup is to use metallic junctions rather than semiconductors as thermoelectric devices. Metals have orders of magnitude more electrons and electronic conductivities higher than semiconductors, but thermal conductivity is higher as well. To evaluate the viability of metallic junction thermoelectrics, a two dimensional heat transfer MATLAB simulation was constructed to calculate efficiency and power output. High Seebeck coefficient alloys, Chromel (90%Ni-10%Cr) and Constantan (55%Cu-45%Ni), produced efficiencies of around 20-30%. Parameters such as the number of layers of junctions, lateral junction density, and junction sizes for both series- and parallel-connected junctions were explored.

Valley excitons in two-dimensional semiconductors

DOE PAGES

Yu, Hongyi; Cui, Xiaodong; Xu, Xiaodong; ...

2014-12-30

Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibitmore » remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.« less

High efficiency low cost thin film silicon solar cell design and method for making

DOEpatents

Sopori, B.L.

1999-04-27

A semiconductor device is described having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer. 9 figs.

Distributed gain in plasmonic reflectors and its use for terahertz generation.

PubMed

Sydoruk, O; Syms, R R A; Solymar, L

2012-08-27

Semiconductor plasmons have potential for terahertz generation. Because practical device formats may be quasi-optical, we studied theoretically distributed plasmonic reflectors that comprise multiple interfaces between cascaded two-dimensional electron channels. Employing a mode-matching technique, we show that transmission through and reflection from a single interface depend on the magnitude and direction of a dc current flowing in the channels. As a result, plasmons can be amplified at an interface, and the cumulative effect of multiple interfaces increases the total gain, leading to plasmonic reflection coefficients exceeding unity. Reversing the current direction in a distributed reflector, however, has the opposite effect of plasmonic deamplification. Consequently, we propose structurally asymmetric resonators comprising two different distributed reflectors and predict that they are capable of terahertz oscillations at low threshold currents.

Reconfiguring crystal and electronic structures of MoS 2 by substitutional doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suh, Joonki; Tan, Teck Leong; Zhao, Weijie

Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS 2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valencemore » band maximum of multilayer MoS 2 at the Γ point pushed upward by hybridization with the Nb states. Finally, when thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.« less

Reconfiguring crystal and electronic structures of MoS 2 by substitutional doping

DOE PAGES

Suh, Joonki; Tan, Teck Leong; Zhao, Weijie; ...

2018-01-15

Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS 2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valencemore » band maximum of multilayer MoS 2 at the Γ point pushed upward by hybridization with the Nb states. Finally, when thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.« less

A Two-Dimensional Manganese Gallium Nitride Surface Structure Showing Ferromagnetism at Room Temperature.

PubMed

Ma, Yingqiao; Chinchore, Abhijit V; Smith, Arthur R; Barral, María Andrea; Ferrari, Valeria

2018-01-10

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.

Very-low-power and footprint integrated photonic modulators and switches for ICT

NASA Astrophysics Data System (ADS)

Thylén, Lars; Holmström, Petter; Wosinski, Lech

2013-03-01

The current development in photonics for communications and interconnects pose increasing requirements on reduction of footprint, power dissipation and cost, as well as increased bandwidth. Integrated nanophotonics has been viewed as one solution to this, capitalizing on development in nanotechnology as such as well as on increased insights into light matter interaction on the nanoscale. The latter can be exemplified by plasmonics and low-dimensional semiconductors such as quantum dots (QDs). In this scenario the development of better electrooptic materials is also of great importance, the electrooptic polymers being an example, since they potentially offer improved properties for optical phase modulators in terms of power and probably cost and general flexibility. Phase modulators are essential for e.g. the rapidly developing advanced modulation formats for telecom, since phase modulation basically can generate any type of modulation. The electrooptic polymers, e.g. in combination with plasmonics nanoparticle array waveguides or nanostructured hybrid plasmonic media can theoretically give extremely compact and low power dissipation modulators, still to be demonstrated. The low-dimensional semiconductors, e.g. in the shape of QDs, can be employed for modulation or switching functions, offering possibilities in the future for scaling to 2 or 3 dimensions for advanced switching functions. In both the plasmonics and QD cases, nanosizing and low power dissipation are generally due to near-field interactions, albeit being of different physical origin in the two cases. A comparison of all-optical and electronically controlled switching is given.

Evolution of corundum-structured III-oxide semiconductors: Growth, properties, and devices

NASA Astrophysics Data System (ADS)

Fujita, Shizuo; Oda, Masaya; Kaneko, Kentaro; Hitora, Toshimi

2016-12-01

The recent progress and development of corundum-structured III-oxide semiconductors are reviewed. They allow bandgap engineering from 3.7 to ∼9 eV and function engineering, leading to highly durable electronic devices and deep ultraviolet optical devices as well as multifunctional devices. Mist chemical vapor deposition can be a simple and safe growth technology and is advantageous for reducing energy and cost for the growth. This is favorable for the wide commercial use of devices at low cost. The III-oxide semiconductors are promising candidates for new devices contributing to sustainable social, economic, and technological development for the future.

Integrated three-dimensional module heat exchanger for power electronics cooling

DOEpatents

Bennion, Kevin; Lustbader, Jason

2013-09-24

Embodiments discussed herein are directed to a power semiconductor packaging that removes heat from a semiconductor package through one or more cooling zones that are located in a laterally oriented position with respect to the semiconductor package. Additional embodiments are directed to circuit elements that are constructed from one or more modular power semiconductor packages.

Disordered Phase of the 3x3 Pb/Ge(111) structure at low temperature

NASA Astrophysics Data System (ADS)

Guo, Jiandong; Bolorizadeh, Mehdi; Plummer, E. W.

2003-03-01

* Dept. of Phys., Univ. of Tenn., Knoxville, TN 37996. ** Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. At a metal surface or a thin metallic film on a semiconductor there is a competition between the long-range adatom-adatom interactions and the local stress fields imposed by the substrate bulk structure. In interesting cases this leads to a structural phase transition. In this talk we present a STM investigation of the two-dimensional structure at different temperatures for the 1/3 monolayer of Pb on Ge(111) system. When the temperature is lowered the interface undergoes a (3x3)R30^o to (3x3) phase transition at roughly 110 K. Substitutional Ge defects play a crucial role in the phase transition as has been reported for the isoelectronic Sn/Ge system. However, unlike Sn/Ge, as the temperature is lowed below 80 K the (3x3) structure in Pb/Ge is broken and a disordered glassy-like structure is observed. This is very similar to the glassy phase predicted by Shi et al. in a model calculation for the Sn/Ge system. The question we address is, is this disordered low temperature phase inherent to the ideal Pb/Ge system or a consequence of the Ge substitutional defects? This work was funded by NSF DMR-0105232 and Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725.

Electroactive Nanoporous Metal Oxides and Chalcogenides by Chemical Design

PubMed Central

2017-01-01

The archetypal silica- and aluminosilicate-based zeolite-type materials are renowned for wide-ranging applications in heterogeneous catalysis, gas-separation and ion-exchange. Their compositional space can be expanded to include nanoporous metal chalcogenides, exemplified by germanium and tin sulfides and selenides. By comparison with the properties of bulk metal dichalcogenides and their 2D derivatives, these open-framework analogues may be viewed as three-dimensional semiconductors filled with nanometer voids. Applications exist in a range of molecule size and shape discriminating devices. However, what is the electronic structure of nanoporous metal chalcogenides? Herein, materials modeling is used to describe the properties of a homologous series of nanoporous metal chalcogenides denoted np-MX2, where M = Si, Ge, Sn, Pb, and X = O, S, Se, Te, with Sodalite, LTA and aluminum chromium phosphate-1 structure types. Depending on the choice of metal and anion their properties can be tuned from insulators to semiconductors to metals with additional modification achieved through doping, solid solutions, and inclusion (with fullerene, quantum dots, and hole transport materials). These systems form the basis of a new branch of semiconductor nanochemistry in three dimensions. PMID:28572706

Thin film three-dimensional topological insulator metal-oxide-semiconductor field-effect-transistors: A candidate for sub-10 nm devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akhavan, N. D., E-mail: nima.dehdashti@uwa.edu.au; Jolley, G.; Umana-Membreno, G. A.

2014-08-28

Three-dimensional (3D) topological insulators (TI) are a new state of quantum matter in which surface states reside in the bulk insulating energy bandgap and are protected by time-reversal symmetry. It is possible to create an energy bandgap as a consequence of the interaction between the conduction band and valence band surface states from the opposite surfaces of a TI thin film, and the width of the bandgap can be controlled by the thin film thickness. The formation of an energy bandgap raises the possibility of thin-film TI-based metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this paper, we explore the performance of MOSFETs basedmore » on thin film 3D-TI structures by employing quantum ballistic transport simulations using the effective continuous Hamiltonian with fitting parameters extracted from ab-initio calculations. We demonstrate that thin film transistors based on a 3D-TI structure provide similar electrical characteristics compared to a Si-MOSFET for gate lengths down to 10 nm. Thus, such a device can be a potential candidate to replace Si-based MOSFETs in the sub-10 nm regime.« less

GeAs and SiAs monolayers: Novel 2D semiconductors with suitable band structures

NASA Astrophysics Data System (ADS)

Zhou, Liqin; Guo, Yu; Zhao, Jijun

2018-01-01

Two dimensional (2D) materials provide a versatile platform for nanoelectronics, optoelectronics and clean energy conversion. Based on first-principles calculations, we propose a novel kind of 2D materials - GeAs and SiAs monolayers and investigate their atomic structure, thermodynamic stability, and electronic properties. The calculations show that monolayer GeAs and SiAs sheets are energetically and dynamically stable. Their small interlayer cohesion energies (0.191 eV/atom for GeAs and 0.178 eV/atom for SiAs) suggest easy exfoliation from the bulk solids that exist in nature. As 2D semiconductors, GeAs and SiAs monolayers possess band gap of 2.06 eV and 2.50 eV from HSE06 calculations, respectively, while their band gap can be further engineered by the number of layers. The relatively small and anisotropic carrier effective masses imply fast electric transport in these 2D semiconductors. In particular, monolayer SiAs is a direct gap semiconductor and a potential photocatalyst for water splitting. These theoretical results shine light on utilization of monolayer or few-layer GeAs and SiAs materials for the next-generation 2D electronics and optoelectronics with high performance and satisfactory stability.

Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts.

PubMed

Tang, Cindy G; Ang, Mervin C Y; Choo, Kim-Kian; Keerthi, Venu; Tan, Jun-Kai; Syafiqah, Mazlan Nur; Kugler, Thomas; Burroughes, Jeremy H; Png, Rui-Qi; Chua, Lay-Lay; Ho, Peter K H

2016-11-24

To make high-performance semiconductor devices, a good ohmic contact between the electrode and the semiconductor layer is required to inject the maximum current density across the contact. Achieving ohmic contacts requires electrodes with high and low work functions to inject holes and electrons respectively, where the work function is the minimum energy required to remove an electron from the Fermi level of the electrode to the vacuum level. However, it is challenging to produce electrically conducting films with sufficiently high or low work functions, especially for solution-processed semiconductor devices. Hole-doped polymer organic semiconductors are available in a limited work-function range, but hole-doped materials with ultrahigh work functions and, especially, electron-doped materials with low to ultralow work functions are not yet available. The key challenges are stabilizing the thin films against de-doping and suppressing dopant migration. Here we report a general strategy to overcome these limitations and achieve solution-processed doped films over a wide range of work functions (3.0-5.8 electronvolts), by charge-doping of conjugated polyelectrolytes and then internal ion-exchange to give self-compensated heavily doped polymers. Mobile carriers on the polymer backbone in these materials are compensated by covalently bonded counter-ions. Although our self-compensated doped polymers superficially resemble self-doped polymers, they are generated by separate charge-carrier doping and compensation steps, which enables the use of strong dopants to access extreme work functions. We demonstrate solution-processed ohmic contacts for high-performance organic light-emitting diodes, solar cells, photodiodes and transistors, including ohmic injection of both carrier types into polyfluorene-the benchmark wide-bandgap blue-light-emitting polymer organic semiconductor. We also show that metal electrodes can be transformed into highly efficient hole- and electron-injection contacts via the self-assembly of these doped polyelectrolytes. This consequently allows ambipolar field-effect transistors to be transformed into high-performance p- and n-channel transistors. Our strategy provides a method for producing ohmic contacts not only for organic semiconductors, but potentially for other advanced semiconductors as well, including perovskites, quantum dots, nanotubes and two-dimensional materials.

The semiconductor waveguide facet reflectivity problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herzinger, C.M.; Lu, C.C.; DeTemple, T.A.

1993-08-01

The problem of the facet reflectivity of a semiconductor slab waveguide is reexamined as an extension of Ikegami's original approach but which includes radiation-like modes. The latter are included, using a guide-within-a-guide geometry, as modes bound to a thick air-cladding guide which contains the core profile of interest. In this model with a relatively simple analysis, the coupling from the fundamental mode to radiation modes can be analyzed. The cross-coupling to the radiation modes is considered in detail for the simple double heterostructure waveguide and is shown to be important only for large core-cladding index differences and for strong modalmore » confinement wherein it results in a true facet loss. The conditions for this are the same as for low threshold lasers so that the loss sets a maximum limit on the equivalent internal quantum efficiency. A separate one-dimensional finite element, numerical mode matching program, which treats evanescent and propagating radiation modes, is used as a comparison. The two methods of accounting for radiation modes are shown to be in good agreement: both predict reduced extremes in reflectivity when compared with the original Ikegami model. Modern graded core cases are treated as general examples along with the specific quantum well laser structures taken from the literature. These include II-VI and III-V structures spanning wavelengths from 0.5 [mu]m to 10.0 [mu]m.« less

Ge/IIIV fin field-effect transistor common gate process and numerical simulations

NASA Astrophysics Data System (ADS)

Chen, Bo-Yuan; Chen, Jiann-Lin; Chu, Chun-Lin; Luo, Guang-Li; Lee, Shyong; Chang, Edward Yi

2017-04-01

This study investigates the manufacturing process of thermal atomic layer deposition (ALD) and analyzes its thermal and physical mechanisms. Moreover, experimental observations and computational fluid dynamics (CFD) are both used to investigate the formation and deposition rate of a film for precisely controlling the thickness and structure of the deposited material. First, the design of the TALD system model is analyzed, and then CFD is used to simulate the optimal parameters, such as gas flow and the thermal, pressure, and concentration fields, in the manufacturing process to assist the fabrication of oxide-semiconductors and devices based on them, and to improve their characteristics. In addition, the experiment applies ALD to grow films on Ge and GaAs substrates with three-dimensional (3-D) transistors having high electric performance. The electrical analysis of dielectric properties, leakage current density, and trapped charges for the transistors is conducted by high- and low-frequency measurement instruments to determine the optimal conditions for 3-D device fabrication. It is anticipated that the competitive strength of such devices in the semiconductor industry will be enhanced by the reduction of cost and improvement of device performance through these optimizations.

Low-temperature magnetotransport of the narrow-gap semiconductor FeSb2

NASA Astrophysics Data System (ADS)

Takahashi, H.; Okazaki, R.; Yasui, Y.; Terasaki, I.

2011-11-01

We present a study of the magnetoresistance and Hall effect in the narrow-gap semiconductor FeSb2 at low temperatures. Both the electrical and Hall resistivities show unusual magnetic field dependence in the low-temperature range where a large Seebeck coefficient was observed. By applying a two-carrier model, we find that the carrier concentration decreases from 1 down to 10-4 ppm/unit cell and the mobility increases from 2000 to 28 000 cm2/Vs with decreasing temperature from 30 down to 4 K. At lower temperatures, the magnetoresistive behavior drastically changes and a negative magnetoresistance is observed at 3 K. These low-temperature behaviors are reminiscent of the low-temperature magnetotransport observed in doped semiconductors such as As-doped Ge, which is well described by a weak-localization picture. We argue a detailed electronic structure in FeSb2 inferred from our observations.

Emerging technologies for high performance infrared detectors

NASA Astrophysics Data System (ADS)

Tan, Chee Leong; Mohseni, Hooman

2018-01-01

Infrared photodetectors (IRPDs) have become important devices in various applications such as night vision, military missile tracking, medical imaging, industry defect imaging, environmental sensing, and exoplanet exploration. Mature semiconductor technologies such as mercury cadmium telluride and III-V material-based photodetectors have been dominating the industry. However, in the last few decades, significant funding and research has been focused to improve the performance of IRPDs such as lowering the fabrication cost, simplifying the fabrication processes, increasing the production yield, and increasing the operating temperature by making use of advances in nanofabrication and nanotechnology. We will first review the nanomaterial with suitable electronic and mechanical properties, such as two-dimensional material, graphene, transition metal dichalcogenides, and metal oxides. We compare these with more traditional low-dimensional material such as quantum well, quantum dot, quantum dot in well, semiconductor superlattice, nanowires, nanotube, and colloid quantum dot. We will also review the nanostructures used for enhanced light-matter interaction to boost the IRPD sensitivity. These include nanostructured antireflection coatings, optical antennas, plasmonic, and metamaterials.

Accurate calculation of field and carrier distributions in doped semiconductors

NASA Astrophysics Data System (ADS)

Yang, Wenji; Tang, Jianping; Yu, Hongchun; Wang, Yanguo

2012-06-01

We use the numerical squeezing algorithm(NSA) combined with the shooting method to accurately calculate the built-in fields and carrier distributions in doped silicon films (SFs) in the micron and sub-micron thickness range and results are presented in graphical form for variety of doping profiles under different boundary conditions. As a complementary approach, we also present the methods and the results of the inverse problem (IVP) - finding out the doping profile in the SFs for given field distribution. The solution of the IVP provides us the approach to arbitrarily design field distribution in SFs - which is very important for low dimensional (LD) systems and device designing. Further more, the solution of the IVP is both direct and much easy for all the one-, two-, and three-dimensional semiconductor systems. With current efforts focused on the LD physics, knowing of the field and carrier distribution details in the LD systems will facilitate further researches on other aspects and hence the current work provides a platform for those researches.

Quantized conductance doubling and hard gap in a two-dimensional semiconductor–superconductor heterostructure

PubMed Central

Kjaergaard, M.; Nichele, F.; Suominen, H. J.; Nowak, M. P.; Wimmer, M.; Akhmerov, A. R.; Folk, J. A.; Flensberg, K.; Shabani, J.; Palmstrøm, C. J.; Marcus, C. M.

2016-01-01

Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards topological matter is by coupling a 2D electron gas with strong spin–orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e2/h, consistent with theory. The hard-gap semiconductor–superconductor system demonstrated here is amenable to top-down processing and provides a new avenue towards low-dissipation electronics and topological quantum systems. PMID:27682268

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

NASA Astrophysics Data System (ADS)

Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-02-01

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (~1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals.

PubMed

Carey, Benjamin J; Ou, Jian Zhen; Clark, Rhiannon M; Berean, Kyle J; Zavabeti, Ali; Chesman, Anthony S R; Russo, Salvy P; Lau, Desmond W M; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C; Dickey, Michael D; Kaner, Richard B; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-02-17

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

PubMed Central

Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kavehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-01-01

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes. PMID:28211538

Growing Cobalt Silicide Columns In Silicon

NASA Technical Reports Server (NTRS)

Fathauer, Obert W.

1991-01-01

Codeposition by molecular-beam epitaxy yields variety of structures. Proposed fabrication process produces three-dimensional nanometer-sized structures on silicon wafers. Enables control of dimensions of metal and semiconductor epitaxial layers in three dimensions instead of usual single dimension (perpendicular to the plane of the substrate). Process used to make arrays of highly efficient infrared sensors, high-speed transistors, and quantum wires. For fabrication of electronic devices, both shapes and locations of columns controlled. One possible technique for doing this electron-beam lithography, see "Making Submicron CoSi2 Structures on Silicon Substrates" (NPO-17736).

Three-dimensional patterning methods and related devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Putnam, Morgan C.; Kelzenberg, Michael D.; Atwater, Harry A.

2016-12-27

Three-dimensional patterning methods of a three-dimensional microstructure, such as a semiconductor wire array, are described, in conjunction with etching and/or deposition steps to pattern the three-dimensional microstructure.

A General Strategy to Achieve Colossal Permittivity and Low Dielectric Loss Through Constructing Insulator/Semiconductor/Insulator Multilayer Structures

NASA Astrophysics Data System (ADS)

Liu, Kai; Sun, Yalong; Zheng, Fengang; Tse, Mei-Yan; Sun, Qingbo; Liu, Yun; Hao, Jianhua

2018-06-01

In this work, we propose a route to realize high-performance colossal permittivity (CP) by creating multilayer structures of insulator/semiconductor/insulator. To prove the new concept, we made heavily reduced rutile TiO2 via annealing route in Ar/H2 atmosphere. Dielectric studies show that the maximum dielectric permittivity ( 3.0 × 104) of our prepared samples is about 100 times higher than that ( 300) of conventional TiO2. The minimum dielectric loss is 0.03 (at 104-105 Hz). Furthermore, CP is almost independent of the frequency (100-106 Hz) and the temperature (20-350 K). We suggest that the colossal permittivity is attributed to the high carrier concentration of the inner TiO2 semiconductor, while the low dielectric loss is due to the presentation of the insulator layer on the surface of TiO2. The method proposed here can be expanded to other material systems, such as semiconductor Si sandwiched by top and bottom insulator layers of Ga2O3.

Room-temperature semiconductor heterostructure refrigeration

NASA Astrophysics Data System (ADS)

Chao, K. A.; Larsson, Magnus; Mal'shukov, A. G.

2005-07-01

With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5-7K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.

Growth and electrical characterization of two-dimensional layered MoS{sub 2}/SiC heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Edwin W.; Nath, Digbijoy N.; Lee, Choong Hee

2014-11-17

The growth and electrical characterization of the heterojunction formed between two-dimensional (2D) layered p-molybdenum disulfide (MoS{sub 2}) and nitrogen-doped 4H silicon carbide (SiC) are reported. The integration of 2D semiconductors with the conventional three-dimensional (3D) substrates could enable semiconductor heterostructures with unprecedented properties. In this work, direct growth of p-type MoS{sub 2} films on SiC was demonstrated using chemical vapor deposition, and the MoS{sub 2} films were found to be high quality based on x-ray diffraction and Raman spectra. The resulting heterojunction was found to display rectification and current-voltage characteristics consistent with a diode for which forward conduction in themore » low-bias region is dominated by multi-step recombination tunneling. Capacitance-voltage measurements were used to determine the built-in voltage for the p-MoS{sub 2}/n-SiC heterojunction diode, and we propose an energy band line up for the heterostructure based on these observations. The demonstration of heterogeneous material integration between MoS{sub 2} and SiC enables a promising new class of 2D/3D heterostructures.« less

Penta-SiC5 monolayer: A novel quasi-planar indirect semiconductor with a tunable wide band gap

NASA Astrophysics Data System (ADS)

Naseri, Mosayeb

2018-03-01

In this paper, by using of the first principles calculations in the framework of the density functional theory, we systematically investigated the structure, stability, electronic and optical properties of a novel two-dimensional pentagonal monolayer semiconductors namely penta-SiC5 monolayer. Comparing elemental silicon, diamond, and previously reported 2D carbon allotropes, our calculation shows that the predicted penta-SiC5 monolayer has a metastable nature. The calculated results indicate that the predicted monolayer is an indirect semiconductor with a wide band gap of about 2.82 eV by using Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional level of theory which can be effectively tuned by external biaxial strains. The obtained exceptional electronic properties suggest penta-SiC5 monolayer as promising candidates for application in new electronic devices in nano scale.

Three- and Two-Dimensional Tin and Lead Halide Perovskite Semiconductors: Synthesis and Application in Photovoltaics

NASA Astrophysics Data System (ADS)

Cao, Duyen Hanh

Halide perovskites, AMX3 (A = monocation, B = Ge, Sn, or Pb, and X = halogen), present a versatile class of solution-processable semiconductors made from earth abundant materials with outstanding electrical and optical properties. Their solar cell efficiencies have dramatically increased from 9% to 22% in less than five years since 2012, a rate that has never been seen before in photovoltaic research. Critical to the final goal of commercializing perovskite solar cell technology is achieving device long-term stability and eliminating toxic elements in device components. This thesis uses 3D AMX 3 perovskites as a stand-in to develop a new class of lead-free, moisture stable, functional and highly tunable 2D Ruddlesden-Popper (BA) 2(MA)n-1SnnI3n+1 (n is an integer) perovskite semiconductors. Synthesis, thin film fabrication, extensive characterization, and solar cell device structure-performance relationships are presented throughout the entire thesis.

Visible light active 2D C3N4-CdS hetero-junction photocatalyst for effective removal of azo dye by photodegradation

NASA Astrophysics Data System (ADS)

Ghosh Chaudhuri, Rajib; Chaturvedi, Ashwin; Iype, Eldhose

2018-03-01

A hetero-junction two dimensional photocatalyst that consists of organic semiconductor carbon nitride (C3N4) and inorganic semiconductor CdS, which acts as the light harvesting units and heterogeneous catalyst, was developed for the degradation of azo dye methyl orange (MO). Both materials are visible light active semiconductor. So the effective band gap of this heterojunction materials does not significantly change the visible light activity, but the injection of electrons from excited C3N4 to CdS increases the stability of hole-electron pair and that ultimately enhances the photocatalytic activity. This heterojunction catalyst finally can remove 97% of dyes and that is comparatively higher than individual pure materials. Finally, by using DFT analysis the band structure and the level diagrams of this photocatalyst are also analyzed.

Luminescence in Conjugated Molecular Materials under Sub-bandgap Excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

So, Franky

2014-05-08

Light emission in semiconductors occurs when they are under optical and electrical excitation with energy larger than the bandgap energy. In some low-dimensional semiconductor heterostructure systems, this thermodynamic limit can be violated due to radiative Auger recombination (AR), a process in which the sub-bandgap energy released from a recombined electron-hole pair is transferred to a third particle leading to radiative band-to-band recombination.1 Thus far, photoluminescence up-conversion phenomenon has been observed in some low dimensional semiconductor systems, and the effect is very weak and it can only be observed at low temperatures. Recently, we discovered that efficient electroluminescence in poly[2-methoxy-5-(2’-ethylhexyloxy)-1, phenylenevinylene]more » (MEH-PPV) polymer light-emitting devices (PLEDs) at drive voltages below its bandgap voltage could be observed when a ZnO nanoparticles (NPs) electron injection layer was inserted between the polymer and the aluminum electrode. Specifically, emitted photons with energy of 2.13 eV can be detected at operating voltages as low as 1.2 V at room temperature. Based on these data, we propose that the sub-bandgap turn-on in the MEH-PPV device is due to an Auger-assisted energy up-conversion process. The significance of this discovery is three-fold. First, radiative recombination occurs at operating voltages below the thermodynamic bandgap voltage. This process can significantly reduce the device operating voltage. For example, the current density of the device with the ZnO NC layer is almost two orders of magnitude higher than that of the device without the NC layer. Second, a reactive metal is no longer needed for the cathode. Third, this electroluminescence up-conversion process can be applied to inorganic semiconductors systems as well and their operation voltages of inorganic LEDs can be reduced to about half of the bandgap energy. Based on our initial data, we propose that the sub-bandgap turn-on in MEH-PPV devices is due to Auger-assisted energy up-conversion process. Specifically, we propose that the up-conversion process is due to charge accumulation at the polymer/NPs interface. This model requires that holes should be the dominant carriers in the polymer and the polymer/ZnO NCs heterojunction should be a type II alignment. In order to determine the mechanism of the up-conversion process, we will characterize devices fabricated using polymers with different carrier transporting properties to determine whether hole accumulation at the polymer/nanocrystals is required. Likewise, we will also use NPs with different electronic structures to fabricate devices to determine how electron accumulation affects the up-conversion process. Finally, we will measure quantitatively the interface charge accumulation by electroabsorption and correlate the results with the up-conversion photoluminescence efficiency measurements under an applied electric field.« less

Group III-arsenide-nitride long wavelength laser diodes

NASA Astrophysics Data System (ADS)

Coldren, Christopher W.

Semiconductor laser diodes transmitting data over silica optical fiber form the backbone of modern day communications systems, enabling terabit per second data transmission over hundreds to thousands of kilometers of distance. The wavelength of emission of the transmission semiconductor laser diode is a critical parameter that determines the performance of the communications system. In high performance fiber optic communications systems, lasers emitting at 1300nm and 1550nm are used because of the low loss and distortion properties of the fiber in these spectral windows. The available lasers today that operate in these fiber optic transmission windows suffer from high cost and poor performance under the typical environmental conditions and require costly and unreliable cooling systems. This dissertation presents work that demonstrates that it is possible to make lasers devices with 1300nm laser emission that are compatible with low cost and operation under extreme operating conditions. The key enabling technology developed is a novel semiconductor material based structure. A group III-Arsenide-Nitride quantum well structure was developed that can be grown expitaxially on GaAs substrates. The properties of this group III-Arsenide-Nitride structure allowed high performance edge emitting and vertical cavity surface emitting lasers to be fabricated which exhibited low threshold currents and low sensitivity to operating temperature.

One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films.

PubMed

Giri, Gaurav; Li, Ruipeng; Smilgies, Detlef-M; Li, Er Qiang; Diao, Ying; Lenn, Kristina M; Chiu, Melanie; Lin, Debora W; Allen, Ranulfo; Reinspach, Julia; Mannsfeld, Stefan C B; Thoroddsen, Sigurdur T; Clancy, Paulette; Bao, Zhenan; Amassian, Aram

2014-04-16

A crystal's structure has significant impact on its resulting biological, physical, optical and electronic properties. In organic electronics, 6,13(bis-triisopropylsilylethynyl)pentacene (TIPS-pentacene), a small-molecule organic semiconductor, adopts metastable polymorphs possessing significantly faster charge transport than the equilibrium crystal when deposited using the solution-shearing method. Here, we use a combination of high-speed polarized optical microscopy, in situ microbeam grazing incidence wide-angle X-ray-scattering and molecular simulations to understand the mechanism behind formation of metastable TIPS-pentacene polymorphs. We observe that thin-film crystallization occurs first at the air-solution interface, and nanoscale vertical spatial confinement of the solution results in formation of metastable polymorphs, a one-dimensional and large-area analogy to crystallization of polymorphs in nanoporous matrices. We demonstrate that metastable polymorphism can be tuned with unprecedented control and produced over large areas by either varying physical confinement conditions or by tuning energetic conditions during crystallization through use of solvent molecules of various sizes.

Single frequency free-running low noise compact extended-cavity semiconductor laser at high power level

NASA Astrophysics Data System (ADS)

Garnache, Arnaud; Myara, Mikhaël.; Laurain, A.; Bouchier, Aude; Perez, J. P.; Signoret, P.; Sagnes, I.; Romanini, D.

2017-11-01

We present a highly coherent semiconductor laser device formed by a ½-VCSEL structure and an external concave mirror in a millimetre high finesse stable cavity. The quantum well structure is diode-pumped by a commercial single mode GaAs laser diode system. This free running low noise tunable single-frequency laser exhibits >50mW output power in a low divergent circular TEM00 beam with a spectral linewidth below 1kHz and a relative intensity noise close to the quantum limit. This approach ensures, with a compact design, homogeneous gain behaviour and a sufficiently long photon lifetime to reach the oscillation-relaxation-free class-A regime, with a cut off frequency around 10MHz.

Experimental researches on quantum transport in semiconductor two-dimensional electron systems

PubMed Central

Kawaji, Shinji

2008-01-01

The author reviews contribution of Gakushuin University group to the progress of the quantum transport in semiconductor two-dimensional electron systems (2DES) for forty years from the birth of the 2DES in middle of the 1960s till the finding of temperature dependent collapse of the quantized Hall resistance in the beginning of this century. PMID:18941299

One-Dimensional Nanostructures and Devices of II–V Group Semiconductors

PubMed Central

2009-01-01

The II–V group semiconductors, with narrow band gaps, are important materials with many applications in infrared detectors, lasers, solar cells, ultrasonic multipliers, and Hall generators. Since the first report on trumpet-like Zn3P2nanowires, one-dimensional (1-D) nanostructures of II–V group semiconductors have attracted great research attention recently because these special 1-D nanostructures may find applications in fabricating new electronic and optoelectronic nanoscale devices. This article covers the 1-D II–V semiconducting nanostructures that have been synthesized till now, focusing on nanotubes, nanowires, nanobelts, and special nanostructures like heterostructured nanowires. Novel electronic and optoelectronic devices built on 1-D II–V semiconducting nanostructures will also be discussed, which include metal–insulator-semiconductor field-effect transistors, metal-semiconductor field-effect transistors, andp–nheterojunction photodiode. We intent to provide the readers a brief account of these exciting research activities. PMID:20596452

Photoluminescence enhancement of monolayer tungsten disulfide in complicated plasmonic microstructures

NASA Astrophysics Data System (ADS)

Zhou, Yi; Hu, Xiaoyong; Gao, Wei; Song, Hanfa; Chu, Saisai; Yang, Hong; Gong, Qihuang

2018-06-01

Two-dimensional van der Waals materials are interesting for fundamental physics exploration and device applications because of their attractive physical properties. Here, we report a strategy to realize photoluminescence (PL) enhancement of two-dimensional transition-metal dichalcogenides (TMDCs) in the visible range using a plasmonic microstructure with patterned gold nanoantennas and a metal-insulator-semiconductor-insulator-metal structure. The PL intensity was enhanced by a factor of two under Y-polarization due to the increased radiative decay rate by the surface plasmon radiation channel in the gold nanoantennas and the decreased nonradiative decay rate by suppressing exciton quenching in the SiO2 isolation layer. The fluorescence lifetime of monolayer tungsten disulfide in this structure was shorter than that of a sample without patterned gold nanoantennas. Tailoring the light-matter interactions between two-dimensional TMDCs and plasmonic nanostructures may provide highly efficient optoelectronic devices such as TMDC-based light emitters.

Novel fabrication technique of hybrid structure lens array for 3D images

NASA Astrophysics Data System (ADS)

Lee, Junsik; Kim, Junoh; Kim, Cheoljoong; Shin, Dooseub; Koo, Gyohyun; Won, Yong Hyub

2016-03-01

Tunable liquid lens arrays can produce three dimensional images by using electrowetting principle that alters surface tensions by applying voltage. This method has advantages of fast response time and low power consumption. However, it is challenging to fabricate a high fill factor liquid lens array and operate three dimensional images which demand high diopter. This study describes a hybrid structure lens array which has not only a liquid lens array but a solid lens array. A concave-shape lens array is unavoidable when using only the liquid lens array and some voltages are needed to make the lens flat. By placing the solid lens array on the liquid lens array, initial diopter can be positive. To fabricate the hybrid structure lens array, a conventional lithographic process in semiconductor manufacturing is needed. A negative photoresist SU-8 was used as chamber master molds. PDMS and UV adhesive replica molding are done sequentially. Two immiscible liquids, DI water and dodecane, are injected in the fabricated chamber, followed by sealing. The fabricated structure has a 20 by 20 pattern of cylindrical shaped circle array and the aperture size of each lens is 1mm. The thickness of the overall hybrid structure is about 2.8mm. Hybrid structure lens array has many advantages. Solid lens array has almost 100% fill factor and allow high efficiency. Diopter can be increased by more than 200 and negative diopter can be shifted to the positive region. This experiment showed several properties of the hybrid structure and demonstrated its superiority.

Photovoltaic and photoelectrochemical conversion of solar energy.

PubMed

Grätzel, Michael

2007-04-15

The Sun provides approximately 100,000 terawatts to the Earth which is about 10000 times more than the present rate of the world's present energy consumption. Photovoltaic cells are being increasingly used to tap into this huge resource and will play a key role in future sustainable energy systems. So far, solid-state junction devices, usually made of silicon, crystalline or amorphous, and profiting from the experience and material availability resulting from the semiconductor industry, have dominated photovoltaic solar energy converters. These systems have by now attained a mature state serving a rapidly growing market, expected to rise to 300 GW by 2030. However, the cost of photovoltaic electricity production is still too high to be competitive with nuclear or fossil energy. Thin film photovoltaic cells made of CuInSe or CdTe are being increasingly employed along with amorphous silicon. The recently discovered cells based on mesoscopic inorganic or organic semiconductors commonly referred to as 'bulk' junctions due to their three-dimensional structure are very attractive alternatives which offer the prospect of very low cost fabrication. The prototype of this family of devices is the dye-sensitized solar cell (DSC), which accomplishes the optical absorption and the charge separation processes by the association of a sensitizer as light-absorbing material with a wide band gap semiconductor of mesoporous or nanocrystalline morphology. Research is booming also in the area of third generation photovoltaic cells where multi-junction devices and a recent breakthrough concerning multiple carrier generation in quantum dot absorbers offer promising perspectives.

Low-voltage organic electronics based on a gate-tunable injection barrier in vertical graphene-organic semiconductor heterostructures.

PubMed

Hlaing, Htay; Kim, Chang-Hyun; Carta, Fabio; Nam, Chang-Yong; Barton, Rob A; Petrone, Nicholas; Hone, James; Kymissis, Ioannis

2015-01-14

The vertical integration of graphene with inorganic semiconductors, oxide semiconductors, and newly emerging layered materials has recently been demonstrated as a promising route toward novel electronic and optoelectronic devices. Here, we report organic thin film transistors based on vertical heterojunctions of graphene and organic semiconductors. In these thin heterostructure devices, current modulation is accomplished by tuning of the injection barriers at the semiconductor/graphene interface with the application of a gate voltage. N-channel devices fabricated with a thin layer of C60 show a room temperature on/off ratio >10(4) and current density of up to 44 mAcm(-2). Because of the ultrashort channel intrinsic to the vertical structure, the device is fully operational at a driving voltage of 200 mV. A complementary p-channel device is also investigated, and a logic inverter based on two complementary transistors is demonstrated. The vertical integration of graphene with organic semiconductors via simple, scalable, and low-temperature fabrication processes opens up new opportunities to realize flexible, transparent organic electronic, and optoelectronic devices.

Atomically thin two-dimensional organic-inorganic hybrid perovskites

NASA Astrophysics Data System (ADS)

Dou, Letian; Wong, Andrew B.; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W.; Fu, Anthony; Bischak, Connor G.; Ma, Jie; Ding, Tina; Ginsberg, Naomi S.; Wang, Lin-Wang; Alivisatos, A. Paul; Yang, Peidong

2015-09-01

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

NASA Astrophysics Data System (ADS)

Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

2014-04-01

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k→) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

Reducing dynamic disorder in small-molecule organic semiconductors by suppressing large-amplitude thermal motions

PubMed Central

Illig, Steffen; Eggeman, Alexander S.; Troisi, Alessandro; Jiang, Lang; Warwick, Chris; Nikolka, Mark; Schweicher, Guillaume; Yeates, Stephen G.; Henri Geerts, Yves; Anthony, John E.; Sirringhaus, Henning

2016-01-01

Thermal vibrations and the dynamic disorder they create can detrimentally affect the transport properties of van der Waals bonded molecular semiconductors. The low-energy nature of these vibrations makes it difficult to access them experimentally, which is why we still lack clear molecular design rules to control and reduce dynamic disorder. In this study we discuss the promising organic semiconductors rubrene, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothio-phene and 2,9-di-decyl-dinaphtho-[2,3-b:20,30-f]-thieno-[3,2-b]-thiophene in terms of an exceptionally low degree of dynamic disorder. In particular, we analyse diffuse scattering in transmission electron microscopy, to show that small molecules that have their side chains attached along the long axis of their conjugated core are better encapsulated in their crystal structure, which helps reduce large-amplitude thermal motions. Our work provides a general strategy for the design of new classes of very high mobility organic semiconductors with a low degree of dynamic disorder. PMID:26898754

Self-assembled ultrathin nanotubes on diamond (100) surface

NASA Astrophysics Data System (ADS)

Lu, Shaohua; Wang, Yanchao; Liu, Hanyu; Miao, Mao-Sheng; Ma, Yanming

2014-04-01

Surfaces of semiconductors are crucially important for electronics, especially when the devices are reduced to the nanoscale. However, surface structures are often elusive, impeding greatly the engineering of devices. Here we develop an efficient method that can automatically explore the surface structures using structure swarm intelligence. Its application to a simple diamond (100) surface reveals an unexpected surface reconstruction featuring self-assembled carbon nanotubes arrays. Such a surface is energetically competitive with the known dimer structure under normal conditions, but it becomes more favourable under a small compressive strain or at high temperatures. The intriguing covalent bonding between neighbouring tubes creates a unique feature of carrier kinetics (that is, one dimensionality of hole states, while two dimensionality of electron states) that could lead to novel design of superior electronics. Our findings highlight that the surface plays vital roles in the fabrication of nanodevices by being a functional part of them.

An evaluation of radiation damage to solid state components flown in low earth orbit satellites.

PubMed

Shin, Myung-Won; Kim, Myung-Hyun

2004-01-01

The effects of total ionising radiation dose upon commercial off-the-shelf semiconductors fitted to satellites operating in low Earth orbit (LEO) conditions was evaluated. The evaluation was performed for the Korea Institute of Technology SATellite-1, (KITSAT-1) which was equipped with commercial solid state components. Two approximate calculation models for space radiation shielding were developed. Verification was performed by comparing the results with detailed three-dimensional calculations using the Monte-Carlo method and measured data from KITSAT-1. It was confirmed that the developed approximate models were reliable for satellite shielding calculations. It was also found that commercial semiconductor devices, which were not radiation hardened, could be damaged within their lifetime due to the total ionising dose they are subject to in the LEO environment. To conclude, an intensive shielding analysis should be considered when commercial devices are used.

Direct solar pumping of semiconductor lasers: A feasibility study

NASA Technical Reports Server (NTRS)

Anderson, Neal G.

1991-01-01

The primary goals of the feasibility study are the following: (1) to provide a preliminary assessment of the feasibility of pumping semiconductor lasers in space directly focused sunlight; and (2) to identify semiconductor laser structures expected to operate at the lowest possible focusing intensities. It should be emphasized that the structures under consideration would provide direct optical-to-optical conversion of sunlight into laser light in a single crystal, in contrast to a configuration consisting of a solar cell or battery electrically pumping a current injection laser. With external modulation, such lasers may prove to be efficient sources for intersatellite communications. We proposed to develop a theoretical model of semiconductor quantum-well lasers photopumped by a broadband source, test it against existing experimental data where possible, and apply it to estimating solar pumping requirements and identifying optimum structures for operation for operation at low pump intensities. This report outlines our progress toward these goals. Discussion of several technical details are left to the attached summary abstract.

Mechanical Properties of Organic Semiconductors for Stretchable, Highly Flexible, and Mechanically Robust Electronics.

PubMed

Root, Samuel E; Savagatrup, Suchol; Printz, Adam D; Rodriquez, Daniel; Lipomi, Darren J

2017-05-10

Mechanical deformability underpins many of the advantages of organic semiconductors. The mechanical properties of these materials are, however, diverse, and the molecular characteristics that permit charge transport can render the materials stiff and brittle. This review is a comprehensive description of the molecular and morphological parameters that govern the mechanical properties of organic semiconductors. Particular attention is paid to ways in which mechanical deformability and electronic performance can coexist. The review begins with a discussion of flexible and stretchable devices of all types, and in particular the unique characteristics of organic semiconductors. It then discusses the mechanical properties most relevant to deformable devices. In particular, it describes how low modulus, good adhesion, and absolute extensibility prior to fracture enable robust performance, along with mechanical "imperceptibility" if worn on the skin. A description of techniques of metrology precedes a discussion of the mechanical properties of three classes of organic semiconductors: π-conjugated polymers, small molecules, and composites. The discussion of each class of materials focuses on molecular structure and how this structure (and postdeposition processing) influences the solid-state packing structure and thus the mechanical properties. The review concludes with applications of organic semiconductor devices in which every component is intrinsically stretchable or highly flexible.

Three-dimensional charge transport in organic semiconductor single crystals.

PubMed

He, Tao; Zhang, Xiying; Jia, Jiong; Li, Yexin; Tao, Xutang

2012-04-24

Three-dimensional charge transport anisotropy in organic semiconductor single crystals - both plates and rods (above and below, respectively, in the figure) - is measured in well-performing organic field-effect transistors for the first time. The results provide an excellent model for molecular design and device preparation that leads to good performance. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low threshold distributed Bragg reflector surface emitting laser diode with semiconductor air-bridge-supported top mirror

NASA Astrophysics Data System (ADS)

Hsin, W.; Du, G.; Gamelin, J. K.; Malloy, K. J.; Wang, S.

1990-03-01

A surface emitting laser diode (SELD) with two distributed Bragg reflectors (DBR) and semiconductor multilayer air-bridge-supported top mirror is fabricated. A low threshold current of 1.5 mA is achieved under room temperature CW operation. The spectrum shows a strong peak at 891 nm with a FWHM of 10 A. With light emission from the top Bragg reflector instead of from the back side of the substrate, laser arrays are easily formed with this novel structure.

Biotechnology Opens New Routes to High-Performance Materials for Improved Photovoltaics, Batteries, Uncooled IR Detectors, Ferroelectrics and Optical Applications

DTIC Science & Technology

2006-11-01

for High Power-Density, Safe Batteries and Solar Energy applications Cloning reveals: Protein template is an enzyme catalyst: γ- Ga2O3 Enzyme that...catalyzes & templates synthesis of silica at low temperature also makes semiconductors from molecular precursors: TiO2 , Ga2O3 , ZnO...CoO, RuOx (311) γ- Ga2O3 Low-temperature catalysis & templating of semiconductor synthesis The catalyst IS the template! Catalytic & Structure

Nanophase diagram of binary eutectic Au-Ge nanoalloys for vapor-liquid-solid semiconductor nanowires growth

NASA Astrophysics Data System (ADS)

Lu, Haiming; Meng, Xiangkang

2015-06-01

Although the vapor-liquid-solid growth of semiconductor nanowire is a non-equilibrium process, the equilibrium phase diagram of binary alloy provides important guidance on the growth conditions, such as the temperature and the equilibrium composition of the alloy. Given the small dimensions of the alloy seeds and the nanowires, the known phase diagram of bulk binary alloy cannot be expected to accurately predict the behavior of the nanowire growth. Here, we developed a unified model to describe the size- and dimensionality-dependent equilibrium phase diagram of Au-Ge binary eutectic nanoalloys based on the size-dependent cohesive energy model. It is found that the liquidus curves reduce and shift leftward with decreasing size and dimensionality. Moreover, the effects of size and dimensionality on the eutectic composition are small and negligible when both components in binary eutectic alloys have the same dimensionality. However, when two components have different dimensionality (e.g. Au nanoparticle-Ge nanowire usually used in the semiconductor nanowires growth), the eutectic composition reduces with decreasing size.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Sanjeev, E-mail: sanjeevsharma145@gmail.com; Kumar, Rajendra, E-mail: khundrakpam-ss@yahoo.com; Singh, Kh. S., E-mail: khundrakpam-ss@yahoo.com

A simple design of broadband one dimensional dielectric/semiconductor multilayer structure having refractive index profile of exponentially graded material has been proposed. The theoretical analysis shows that the proposed structure works as a perfect mirror within a certain wavelength range (1550 nm). In order to calculate the reflection properties a transfer matrix method (TMM) has been used. This property shows that binary graded photonic crystal structures have widened omnidirectional reflector (ODR) bandgap. Hence a exponentially graded photonic crystal structure can be used as a broadband optical reflector and the range of reflection can be tuned to any wavelength region by varying themore » refractive index profile of exponentially graded photonic crystal structure.« less

Bottom-up synthesis of multifunctional nanoporous graphene

NASA Astrophysics Data System (ADS)

Moreno, César; Vilas-Varela, Manuel; Kretz, Bernhard; Garcia-Lekue, Aran; Costache, Marius V.; Paradinas, Markos; Panighel, Mirko; Ceballos, Gustavo; Valenzuela, Sergio O.; Peña, Diego; Mugarza, Aitor

2018-04-01

Nanosize pores can turn semimetallic graphene into a semiconductor and, from being impermeable, into the most efficient molecular-sieve membrane. However, scaling the pores down to the nanometer, while fulfilling the tight structural constraints imposed by applications, represents an enormous challenge for present top-down strategies. Here we report a bottom-up method to synthesize nanoporous graphene comprising an ordered array of pores separated by ribbons, which can be tuned down to the 1-nanometer range. The size, density, morphology, and chemical composition of the pores are defined with atomic precision by the design of the molecular precursors. Our electronic characterization further reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ∼1 electron volt coexist with confined pore states, making the nanoporous graphene a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species.

Nondestructive Memory Elements Based on Polymeric Langmuir-Blodgett Thin Films

NASA Astrophysics Data System (ADS)

Reece, T. J.; Ducharme, S.

2007-03-01

Ferroelectric field effect transistors (FeFETs) have attracted much attention recently because of their low power consumption and fast nondestructive readout. Among the ferroelectric thin films used in FET devices; the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C2H2F2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, low cost and compatibility with organic semiconductors. By employing the Langmuir-Blodgett technique, we are able to deposit films as thin as 1.8 nm. We discuss the characterization, modeling and fabrication of metal-ferroelectric-insulator-semiconductor (MFIS) structures incorporating these films.

Three-dimensional hot electron photovoltaic device with vertically aligned TiO2 nanotubes.

PubMed

Goddeti, Kalyan C; Lee, Changhwan; Lee, Young Keun; Park, Jeong Young

2018-05-09

Titanium dioxide (TiO 2 ) nanotubes with vertically aligned array structures show substantial advantages in solar cells as an electron transport material that offers a large surface area where charges travel linearly along the nanotubes. Integrating this one-dimensional semiconductor material with plasmonic metals to create a three-dimensional plasmonic nanodiode can influence solar energy conversion by utilizing the generated hot electrons. Here, we devised plasmonic Au/TiO 2 and Ag/TiO 2 nanodiode architectures composed of TiO 2 nanotube arrays for enhanced photon absorption, and for the subsequent generation and capture of hot carriers. The photocurrents and incident photon to current conversion efficiencies (IPCE) were obtained as a function of photon energy for hot electron detection. We observed enhanced photocurrents and IPCE using the Ag/TiO 2 nanodiode. The strong plasmonic peaks of the Au and Ag from the IPCE clearly indicate an enhancement of the hot electron flux resulting from the presence of surface plasmons. The calculated electric fields and the corresponding absorbances of the nanodiode using finite-difference time-domain simulation methods are also in good agreement with the experimental results. These results show a unique strategy of combining a hot electron photovoltaic device with a three-dimensional architecture, which has the clear advantages of maximizing light absorption and a metal-semiconductor interface area.

Method of making self-aligned lightly-doped-drain structure for MOS transistors

DOEpatents

Weiner, Kurt H.; Carey, Paul G.

2001-01-01

A process for fabricating lightly-doped-drains (LDD) for short-channel metal oxide semiconductor (MOS) transistors. The process utilizes a pulsed laser process to incorporate the dopants, thus eliminating the prior oxide deposition and etching steps. During the process, the silicon in the source/drain region is melted by the laser energy. Impurities from the gas phase diffuse into the molten silicon to appropriately dope the source/drain regions. By controlling the energy of the laser, a lightly-doped-drain can be formed in one processing step. This is accomplished by first using a single high energy laser pulse to melt the silicon to a significant depth and thus the amount of dopants incorporated into the silicon is small. Furthermore, the dopants incorporated during this step diffuse to the edge of the MOS transistor gate structure. Next, many low energy laser pulses are used to heavily dope the source/drain silicon only in a very shallow region. Because of two-dimensional heat transfer at the MOS transistor gate edge, the low energy pulses are inset from the region initially doped by the high energy pulse. By computer control of the laser energy, the single high energy laser pulse and the subsequent low energy laser pulses are carried out in a single operational step to produce a self-aligned lightly-doped-drain-structure.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trump, Benjamin A., E-mail: btrump1@jhu.edu; Department of Physics and Astronomy, Institute for Quantum Matter, Johns Hopkins University, Baltimore, MD 21218; McQueen, Tyrel M., E-mail: mcqueen@jhu.edu

The synthesis and physical properties of the new distorted-Hollandite PbIr{sub 4}Se{sub 8} are reported. Powder X-ray diffraction and transmission electron microscopy show that the structure consists of edge- and corner-sharing IrSe{sub 6} octahedra, with one-dimensional channels occupied by Pb. The structure contains Se-Se anion-anion bonding, leading to an electron count of Pb{sup 2+}(Ir{sup 3+}){sub 4}(Se{sub 2}){sup 2-}(Se{sup 2−}){sub 6}, confirmed by bond-valence sums and diamagnetic behavior. Structural and heat capacity measurements demonstrate disorder on the Pb site, due to the combination of lone-pair effects and the large size of the one-dimensional channels. Comparisons are made to known Hollandite and pseudo-Hollanditemore » structures, which demonstrates that the anion-anion bonding in PbIr{sub 4}Se{sub 8} distorts its structure, to accommodate the Ir{sup 3+} state. An electronic structure calculation indicates semiconductor character with a band gap of 0.76(11) eV.« less

Recent progress in magnetic iron oxide-semiconductor composite nanomaterials as promising photocatalysts

NASA Astrophysics Data System (ADS)

Wu, Wei; Changzhong Jiang, Affc; Roy, Vellaisamy A. L.

2014-11-01

Photocatalytic degradation of toxic organic pollutants is a challenging tasks in ecological and environmental protection. Recent research shows that the magnetic iron oxide-semiconductor composite photocatalytic system can effectively break through the bottleneck of single-component semiconductor oxides with low activity under visible light and the challenging recycling of the photocatalyst from the final products. With high reactivity in visible light, magnetic iron oxide-semiconductors can be exploited as an important magnetic recovery photocatalyst (MRP) with a bright future. On this regard, various composite structures, the charge-transfer mechanism and outstanding properties of magnetic iron oxide-semiconductor composite nanomaterials are sketched. The latest synthesis methods and recent progress in the photocatalytic applications of magnetic iron oxide-semiconductor composite nanomaterials are reviewed. The problems and challenges still need to be resolved and development strategies are discussed.

n-Channel semiconductor materials design for organic complementary circuits.

PubMed

Usta, Hakan; Facchetti, Antonio; Marks, Tobin J

2011-07-19

Organic semiconductors have unique properties compared to traditional inorganic materials such as amorphous or crystalline silicon. Some important advantages include their adaptability to low-temperature processing on flexible substrates, low cost, amenability to high-speed fabrication, and tunable electronic properties. These features are essential for a variety of next-generation electronic products, including low-power flexible displays, inexpensive radio frequency identification (RFID) tags, and printable sensors, among many other applications. Accordingly, the preparation of new materials based on π-conjugated organic molecules or polymers has been a central scientific and technological research focus over the past decade. Currently, p-channel (hole-transporting) materials are the leading class of organic semiconductors. In contrast, high-performance n-channel (electron-transporting) semiconductors are relatively rare, but they are of great significance for the development of plastic electronic devices such as organic field-effect transistors (OFETs). In this Account, we highlight the advances our team has made toward realizing moderately and highly electron-deficient n-channel oligomers and polymers based on oligothiophene, arylenediimide, and (bis)indenofluorene skeletons. We have synthesized and characterized a "library" of structurally related semiconductors, and we have investigated detailed structure-property relationships through optical, electrochemical, thermal, microstructural (both single-crystal and thin-film), and electrical measurements. Our results reveal highly informative correlations between structural parameters at various length scales and charge transport properties. We first discuss oligothiophenes functionalized with perfluoroalkyl and perfluoroarene substituents, which represent the initial examples of high-performance n-channel semiconductors developed in this project. The OFET characteristics of these compounds are presented with an emphasis on structure-property relationships. We then examine the synthesis and properties of carbonyl-functionalized oligomers, which constitute second-generation n-channel oligothiophenes, in both vacuum- and solution-processed FETs. These materials have high carrier mobilities and good air stability. In parallel, exceptionally electron-deficient cyano-functionalized arylenediimide derivatives are discussed as early examples of thermodynamically air-stable, high-performance n-channel semiconductors; they exhibit record electron mobilities of up to 0.64 cm(2)/V·s. Furthermore, we provide an overview of highly soluble ladder-type macromolecular semiconductors as OFET components, which combine ambient stability with solution processibility. A high electron mobility of 0.16 cm(2)/V·s is obtained under ambient conditions for solution-processed films. Finally, examples of polymeric n-channel semiconductors with electron mobilities as high as 0.85 cm(2)/V·s are discussed; these constitute an important advance toward fully printed polymeric electronic circuitry. Density functional theory (DFT) computations reveal important trends in molecular physicochemical and semiconducting properties, which, when combined with experimental data, shed new light on molecular charge transport characteristics. Our data provide the basis for a fundamental understanding of charge transport in high-performance n-channel organic semiconductors. Moreover, our results provide a road map for developing functional, complementary organic circuitry, which requires combining p- and n-channel transistors.

Carrier statistics and quantum capacitance effects on mobility extraction in two-dimensional crystal semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Ma, Nan; Jena, Debdeep

2015-03-01

In this work, the consequence of the high band-edge density of states on the carrier statistics and quantum capacitance in transition metal dichalcogenide two-dimensional semiconductor devices is explored. The study questions the validity of commonly used expressions for extracting carrier densities and field-effect mobilities from the transfer characteristics of transistors with such channel materials. By comparison to experimental data, a new method for the accurate extraction of carrier densities and mobilities is outlined. The work thus highlights a fundamental difference between these materials and traditional semiconductors that must be considered in future experimental measurements.

Low-Dimensional Material: Structure-Property Relationship and Applications in Energy and Environmental Engineering

NASA Astrophysics Data System (ADS)

Xiao, Hang

In the past several decades, low-dimensional materials (0D materials, 1D materials and 2D materials) have attracted much interest from both the experimental and theoretical points of view. Because of the quantum confinement effect, low-dimensional materials have exhibited a kaleidoscope of fascinating phenomena and unusual physical and chemical properties, shedding light on many novel applications. Despite the enormous success has been achieved in the research of low-dimensional materials, there are three fundamental challenges of research in low-dimensional materials: 1) Develop new computational tools to accurately describe the properties of low-dimensional materials with low computational cost. 2) Predict and synthesize new low-dimensional materials with novel properties. 3) Reveal new phenomenon induced by the interaction between low-dimensional materials and the surrounding environment. In this thesis, atomistic modelling tools have been applied to address these challenges. We first developed ReaxFF parameters for phosphorus and hydrogen to give an accurate description of the chemical and mechanical properties of pristine and defected black phosphorene. ReaxFF for P/H is transferable to a wide range of phosphorus and hydrogen containing systems including bulk black phosphorus, blue phosphorene, edge-hydrogenated phosphorene, phosphorus clusters and phosphorus hydride molecules. The potential parameters were obtained by conducting global optimization with respect to a set of reference data generated by extensive ab initio calculations. We extended ReaxFF by adding a 60° correction term which significantly improved the description of phosphorus clusters. Emphasis was placed on the mechanical response of black phosphorene with different types of defects. Compared to the nonreactive SW potential of phosphorene, ReaxFF for P/H systems provides a significant improvement in describing the mechanical properties of the pristine and defected black phosphorene, as well as the thermal stability of phosphorene nanotubes. A counterintuitive phenomenon was observed that single vacancies weaken the black phosphorene more than double vacancies with higher formation energy. Our results also showed that the mechanical response of black phosphorene is more sensitive to defects in the zigzag direction than that in the armchair direction. Since ReaxFF allows straightforward extensions to the heterogeneous systems, such as oxides, nitrides, the proposed ReaxFF parameters for P/H systems also underpinned the reactive force field description of heterogeneous P systems, including P-containing 2D van der Waals heterostructures, oxides, etc. Based on the evolutionary algorithm driven structural search, we proposed a new stable trisulfur dinitride (S3N2) 2D crystal that is a covalent network composed solely of S-N sigma bonds. S3N 2 crystal is dynamically, thermally and chemically stable as confirmed by the computed phonon spectrum and ab initio molecular dynamics simulations. GW calculations showed that the 2D S3N2 crystal is a wide, direct band-gap (3.92 eV) semiconductor with a small hole effective mass. The anisotropic optical response of 2D S3N 2 crystal was revealed by GW-BSE calculations. Our result not only marked the prediction of the first 2D crystal composed of nitrogen and sulfur, but also underpinned potential innovations in 2D electronics, optoelectronics, etc. Inspired by the discovery of S3N2 2D crystal, we proposed a new 2D crystal, diphosphorus trisulfide (P2S3), based on the extensive evolutionary algorithm driven structural search. The 2D P2S3 crystal was confirmed to be dynamically, thermally and chemically stable by the computed phonon spectrum and ab initio molecular dynamics simulations. This 2D crystalline phase of P 2S3 corresponds to the global minimum in the Born-Oppenheimer surface of the phosphorus sulfide monolayers with 2:3 stoichiometry. It is a wide band gap (4.55 eV) semiconductor with P-S ? bonds. The electronic properties of P2S3 structure can be tuned by stacking into multilayer P2S3 structures, forming P2S3 nanoribbons or rolling into P2S3 nanotubes, expanding its potential applications for the emerging field of 2D electronics. Then we showed that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules was investigated by ab initio method. For n = 1-5 water molecules, all the reactants follow a stepwise pathway to the transition state. For n = 6-8 water molecules, all the reactants undergo a direct proton transfer to the transition state with overall lower activation free energy. The activation free energy of the reaction is dramatically reduced from 10.4 to 2.4 kcal/mol as the number of water molecules increases from 1 to 6. Meanwhile, the degree of the hydrolysis of CO32- is significantly increased compared to the bulk water solution scenario. The incomplete hydration shells facilitate the hydrolysis of CO3 2- with few water molecules to be not only thermodynamically favorable but also kinetically favorable. We showed that the chemical kinetics is not likely to constrain the speed of CO2 air capture driven by the humidity-swing. (Abstract shortened by ProQuest.).

Electric field induced spin-polarized current

DOEpatents

Murakami, Shuichi; Nagaosa, Naoto; Zhang, Shoucheng

2006-05-02

A device and a method for generating an electric-field-induced spin current are disclosed. A highly spin-polarized electric current is generated using a semiconductor structure and an applied electric field across the semiconductor structure. The semiconductor structure can be a hole-doped semiconductor having finite or zero bandgap or an undoped semiconductor of zero bandgap. In one embodiment, a device for injecting spin-polarized current into a current output terminal includes a semiconductor structure including first and second electrodes, along a first axis, receiving an applied electric field and a third electrode, along a direction perpendicular to the first axis, providing the spin-polarized current. The semiconductor structure includes a semiconductor material whose spin orbit coupling energy is greater than room temperature (300 Kelvin) times the Boltzmann constant. In one embodiment, the semiconductor structure is a hole-doped semiconductor structure, such as a p-type GaAs semiconductor layer.

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

PubMed Central

Ahn, Cheol Hyoun; Senthil, Karuppanan; Cho, Hyung Koun; Lee, Sang Yeol

2013-01-01

High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm2/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers. PMID:24061388

Three-Dimensional Flexible Complementary Metal-Oxide-Semiconductor Logic Circuits Based On Two-Layer Stacks of Single-Walled Carbon Nanotube Networks.

PubMed

Zhao, Yudan; Li, Qunqing; Xiao, Xiaoyang; Li, Guanhong; Jin, Yuanhao; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

2016-02-23

We have proposed and fabricated stable and repeatable, flexible, single-walled carbon nanotube (SWCNT) thin film transistor (TFT) complementary metal-oxide-semiconductor (CMOS) integrated circuits based on a three-dimensional (3D) structure. Two layers of SWCNT-TFT devices were stacked, where one layer served as n-type devices and the other one served as p-type devices. On the basis of this method, it is able to save at least half of the area required to construct an inverter and make large-scale and high-density integrated CMOS circuits easier to design and manufacture. The 3D flexible CMOS inverter gain can be as high as 40, and the total noise margin is more than 95%. Moreover, the input and output voltage of the inverter are exactly matched for cascading. 3D flexible CMOS NOR, NAND logic gates, and 15-stage ring oscillators were fabricated on PI substrates with high performance as well. Stable electrical properties of these circuits can be obtained with bending radii as small as 3.16 mm, which shows that such a 3D structure is a reliable architecture and suitable for carbon nanotube electrical applications in complex flexible and wearable electronic devices.

Influence of quantizing magnetic field and Rashba effect on indium arsenide metal-oxide-semiconductor structure accumulation capacitance

NASA Astrophysics Data System (ADS)

Kovchavtsev, A. P.; Aksenov, M. S.; Tsarenko, A. V.; Nastovjak, A. E.; Pogosov, A. G.; Pokhabov, D. A.; Tereshchenko, O. E.; Valisheva, N. A.

2018-05-01

The accumulation capacitance oscillations behavior in the n-InAs metal-oxide-semiconductor structures with different densities of the built-in charge (Dbc) and the interface traps (Dit) at temperature 4.2 K in the magnetic field (B) 2-10 T, directed perpendicular to the semiconductor-dielectric interface, is studied. A decrease in the oscillation frequency and an increase in the capacitance oscillation amplitude are observed with the increase in B. At the same time, for a certain surface accumulation band bending, the influence of the Rashba effect, which is expressed in the oscillations decay and breakdown, is traced. The experimental capacitance-voltage curves are in a good agreement with the numeric simulation results of the self-consistent solution of Schrödinger and Poisson equations in the magnetic field, taking into account the quantization, nonparabolicity of dispersion law, and Fermi-Dirac electron statistics, with the allowance for the Rashba effect. The Landau quantum level broadening in a two-dimensional electron gas (Lorentzian-shaped density of states), due to the electron scattering mechanism, linearly depends on the magnetic field. The correlation between the interface electronic properties and the characteristic scattering times was established.

Nanomechanical architecture of semiconductor nanomembranes.

PubMed

Huang, Minghuang; Cavallo, Francesca; Liu, Feng; Lagally, Max G

2011-01-01

Semiconductor nanomembranes are single-crystal sheets with thickness ranging from 5 to 500nm. They are flexible, bondable, and mechanically ultra-compliant. They present a new platform to combine bottom-up and top-down semiconductor processing to fabricate various three-dimensional (3D) nanomechanical architectures, with an unprecedented level of control. The bottom-up part is the self-assembly, via folding, rolling, bending, curling, or other forms of shape change of the nanomembranes, with top-down patterning providing the starting point for these processes. The self-assembly to form 3D structures is driven by elastic strain relaxation. A variety of structures, including tubes, rings, coils, rolled-up "rugs", and periodic wrinkles, has been made by such self-assembly. Their geometry and unique properties suggest many potential applications. In this review, we describe the design of desired nanostructures based on continuum mechanics modelling, definition and fabrication of 2D strained nanomembranes according to the established design, and release of the 2D strained sheet into a 3D or quasi-3D object. We also describe several materials properties of nanomechanical architectures. We discuss potential applications of nanomembrane technology to implement simple and hybrid functionalities.

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

DOE PAGES

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; ...

2015-07-22

The formation of semiconductor heterojunctions and their high density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional (2D) crystalline semiconductors as building blocks in next generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate a process strategy for the formation of lithographically-patterned lateral semiconducting heterojunctions within a single 2D crystal. E-beam lithography is used to pattern MoSe 2 monolayer crystals with SiO 2, and the exposed locations are selectively and totally converted to MoS 2 using pulsed laser deposition (PLD) of sulfur in order to form MoSe 2/MoS 2 heterojunctions in predefinedmore » patterns. The junctions and conversion process are characterized by atomically resolved scanning transmission electron microscopy, photoluminescence, and Raman spectroscopy. This demonstration of lateral semiconductor heterojunction arrays within a single 2D crystal is an essential step for the lateral integration of 2D semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin circuitry.« less

Electronic Structure of Two-Dimensional Hydrocarbon Networks of sp2 and sp3 C Atoms

NASA Astrophysics Data System (ADS)

Fujii, Yasumaru; Maruyama, Mina; Wakabayashi, Katsunori; Nakada, Kyoko; Okada, Susumu

2018-03-01

Based on density functional theory with the generalized gradient approximation, we have investigated the geometric and electronic structures of two-dimensional hexagonal covalent networks consisting of oligoacenes and fourfold coordinated hydrocarbon atoms, which are alternately arranged in a hexagonal manner. All networks were semiconductors with a finite energy gap at the Γ point, which monotonically decreased with the increase of the oligoacene length. As a result of a Kagome network of oligoacene connected through sp3 C atoms, the networks possess peculiar electron states in their valence and conduction bands, which consist of a flat dispersion band and a Dirac cone. The total energy of the networks depends on the oligoacene length and has a minimum for the network comprising naphthalene.

Atomically thin two-dimensional organic-inorganic hybrid perovskites.

PubMed

Dou, Letian; Wong, Andrew B; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W; Fu, Anthony; Bischak, Connor G; Ma, Jie; Ding, Tina; Ginsberg, Naomi S; Wang, Lin-Wang; Alivisatos, A Paul; Yang, Peidong

2015-09-25

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials. Copyright © 2015, American Association for the Advancement of Science.

Structure and properties of microporous titanosilicate determined by first-principles calculations

NASA Astrophysics Data System (ADS)

Ching, W. Y.; Xu, Yong-Nian; Gu, Zong-Quan

1996-12-01

The structure of EST-10, a member of synthetic microporous titanosilicates, was recently determined by an ingenious combination of experimental and simulational techniques. However, the locations of the alkali atoms in the framework remain elusive and its electronic structure is totally unknown. Based on first-principles local density calculations, the possible locations of the alkali atoms are identified and its electronic structure and bonding fully elucidated. ETS-10 is a semiconductor with a direct band gap of 2.33 eV. The Na atoms are likely to locate inside the seven-member ring pore adjacent to the one-dimensional Ti-O-Ti-O- chain.

Evidence for Itinerant Carriers in an Anisotropic Narrow-Gap Semiconductor by Angle-Resolved Photoemission Spectroscopy.

PubMed

Ju, Sailong; Bai, Wei; Wu, Liming; Lin, Hua; Xiao, Chong; Cui, Shengtao; Li, Zhou; Kong, Shuai; Liu, Yi; Liu, Dayong; Zhang, Guobin; Sun, Zhe; Xie, Yi

2018-01-01

The ability to accurately determine the electronic structure of solids has become a key prerequisite for modern functional materials. For example, the precise determination of the electronic structure helps to balance the three thermoelectric parameters, which is the biggest challenge to design high-performance thermoelectric materials. Herein, by high-resolution, angle-resolved photoemission spectroscopy (ARPES), the itinerant carriers in CsBi 4 Te 6 (CBT) are revealed for the first time. CBT is a typical anisotropic, narrow-gap semiconductor used as a practical candidate for low-temperature thermoelectric applications, and p-doped CBT series show superconductivity at relatively low carrier concentrations. The ARPES results show a significantly larger bandwidth near the Fermi surface than calculations, which means the carriers transport anisotropically and itinerantly in CBT. It is reasonable to believe that these newly discovered features of carriers in narrow-gap semiconductors are promising for designing optimal thermoelectric materials and superconductors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A photovoltaic device structure based on internal electron emission.

PubMed

McFarland, Eric W; Tang, Jing

2003-02-06

There has been an active search for cost-effective photovoltaic devices since the development of the first solar cells in the 1950s (refs 1-3). In conventional solid-state solar cells, electron-hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. Here we report a multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal-semiconductor junction Schottky diode. Photoexcited electrons are transferred to the metal and travel ballistically to--and over--the Schottky barrier, so providing the photocurrent output. Low-energy (approximately 1 eV) electrons have surprisingly long ballistic path lengths in noble metals, allowing a large fraction of the electrons to be collected. Unlike conventional cells, the semiconductor in this device serves only for majority charge transport and separation. Devices fabricated using a fluorescein photoreceptor on an Au/TiO2/Ti multilayer structure had typical open-circuit photovoltages of 600-800 mV and short-circuit photocurrents of 10-18 micro A cm(-2) under 100 mW cm(-2) visible band illumination: the internal quantum efficiency (electrons measured per photon absorbed) was 10 per cent. This alternative approach to photovoltaic energy conversion might provide the basis for durable low-cost solar cells using a variety of materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Jiang Ping; Yan, Zhi Shuo; Long, Ji Ying

By using a rigid dicarboxylate ligand, 4,5-di(4′-carboxylphenyl)benzene (H{sub 2}L), two complexes formulated as SrL(DMF)(H{sub 2}O)·(CH{sub 3}CN) (DMF=N,N′-dimethylformamide) (1) and BaL(H{sub 2}O){sub 2} (2) were solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1 and 2 display two-dimensional (2D) layer structures. The two complexes exhibit different electrochemical and photoelectrochemical properties. Their thermal stabilities, cyclic voltammograms, UV–vis absorption and diffuse reflectance spectra and photoluminescence properties have been investigated. The band structures, the total density of states (TDOS) and partial density of states (PDOS) of the two complexes were calculated by CASTEP program. Complex 2 exhibits much higher photocurrent density thanmore » complex 1. The Mott–Schottky plots reveal that complexes 1 and 2 both are p-type semiconductors, which are in agreement with their band structure calculations. - Graphical abstract: Two alkaline earth metal(II) complexes with 2D layer structures are p-type semiconductors, they possess different band structures and density of states. And the Ba(II) complex 2 exhibits much higher photocurrent density than the Sr(II) complex 1.« less

Strain engineering of atomic and electronic structures of few-monolayer-thick GaN

NASA Astrophysics Data System (ADS)

Kolobov, A. V.; Fons, P.; Saito, Y.; Tominaga, J.; Hyot, B.; André, B.

2017-07-01

Two-dimensional (2D) semiconductors possess the potential to ultimately minimize the size of devices and concomitantly drastically reduce the corresponding energy consumption. In addition, materials in their atomic-scale limit often possess properties different from their bulk counterparts paving the way to conceptually novel devices. While graphene and 2D transition-metal dichalcogenides remain the most studied materials, significant interest also exists in the fabrication of atomically thin structures from traditionally 3D semiconductors such as GaN. While in the monolayer limit GaN possesses a graphenelike structure and an indirect band gap, it was recently demonstrated that few-layer GaN acquires a Haeckelite structure in the direction of growth with an effectively direct gap. In this work, we demonstrate the possibility of strain engineering of the atomic and electronic structure of few-monolayer-thick GaN structures, which opens new avenues for their practical application in flexible nanoelectronics and nano-optoelectronics. Our simulations further suggest that due to the weak van der Waals-like interaction between a substrate and an overlayer, the use of a MoS2 substrate may be a promising route to fabricate few-monolayer Haeckelite GaN experimentally.

Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mkhitaryan, V. V.; Dobrovitski, V. V.

2015-08-24

The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and 2, the time dependence of the space-integrated spin polarization P(t) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, whichmore » occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 versus d=3). We investigate in detail the coordinate dependence of the time-integrated spin polarization σ(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while σ(r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.« less

Direct laser writing of topographic features in semiconductor-doped glass

NASA Astrophysics Data System (ADS)

Smuk, Andrei Y.

2000-11-01

Patterning of glass and silica surfaces is important for a number of modern technologies, which depend on these materials for manufacturing of both final products, such as optics, and prototypes for casting and molding. Among the fields that require glass processing on microscopic scale are optics (lenses and arrays, diffractive/holographic elements, waveguides), biotechnology (capillary electrophoresis chips and biochemical libraries) and magnetic media (landing zones for magnetic heads). Currently, standard non-laser techniques for glass surface patterning require complex multi-step processes, such as photolithography. Work carried out at Brown has shown that semiconductor- doped glasses (SDG) allow a single-step patterning process using low power continuous-wave visible lasers. SDG are composite materials, which consist of semiconductor crystallites embedded into glass matrix. In this study, borosilicate glasses doped with CdSxSe1-x nanocrystals were used. Exposure of these materials to a low-power above- the-energy gap laser beam leads to local softening, and subsequent expansion and rapid solidification of the exposed volume, resulting in a nearly spherical topographic feature on the surface. The effects of the incident power, beam configuration, and the exposure time on the formation and final parameters of the microlens were studied. Based on the numerical simulation of the temperature distribution produced by the absorbed Gaussian beam, and the ideas of viscous flow at the temperatures around the glass transition point, a model of lens formation is suggested. The light intensity distribution in the near-field of the growing lens is shown to have a significant effect on the final lens height. Fabrication of dense arrays of microlenses is shown, and the thermal and structural interactions between the neighboring lenses were also studied. Two-dimensional continuous-profile topographic features are achieved by exposure of the moving substrates to the writing beam. By controlling the translation speed and the position of the sample, predefined extended structures, such as diffractive optical elements (blazed gratings, Dammann generators, Fresnel zone plates) can be produced with resolution of ~1μm. Below-the-surface patterning is achieved due to a selective etching of laser-written structures in hydrofluoric acid. Similar selective etching technique was developed for undoped borosilicate glasses by exposure to intense visible and UV radiation.

What Is Moving in Hybrid Halide Perovskite Solar Cells?

PubMed Central

2016-01-01

Conspectus Organic–inorganic semiconductors, which adopt the perovskite crystal structure, have perturbed the landscape of contemporary photovoltaics research. High-efficiency solar cells can be produced with solution-processed active layers. The materials are earth abundant, and the simple processing required suggests that high-throughput and low-cost manufacture at scale should be possible. While these materials bear considerable similarity to traditional inorganic semiconductors, there are notable differences in their optoelectronic behavior. A key distinction of these materials is that they are physically soft, leading to considerable thermally activated motion. In this Account, we discuss the internal motion of methylammonium lead iodide (CH3NH3PbI3) and formamidinium lead iodide ([CH(NH2)2]PbI3), covering: (i) molecular rotation-libration in the cuboctahedral cavity; (ii) drift and diffusion of large electron and hole polarons; (iii) transport of charged ionic defects. These processes give rise to a range of properties that are unconventional for photovoltaic materials, including frequency-dependent permittivity, low electron–hole recombination rates, and current–voltage hysteresis. Multiscale simulations, drawing from electronic structure, ab initio molecular dynamic and Monte Carlo computational techniques, have been combined with neutron diffraction measurements, quasi-elastic neutron scattering, and ultrafast vibrational spectroscopy to qualify the nature and time scales of the motions. Electron and hole motion occurs on a femtosecond time scale. Molecular libration is a sub-picosecond process. Molecular rotations occur with a time constant of several picoseconds depending on the cation. Recent experimental evidence and theoretical models for simultaneous electron and ion transport in these materials has been presented, suggesting they are mixed-mode conductors with similarities to fast-ion conducting metal oxide perovskites developed for battery and fuel cell applications. We expound on the implications of these effects for the photovoltaic action. The temporal behavior displayed by hybrid perovskites introduces a sensitivity in materials characterization to the time and length scale of the measurement, as well as the history of each sample. It also poses significant challenges for accurate materials modeling and device simulations. There are large differences between the average and local crystal structures, and the nature of charge transport is too complex to be described by common one-dimensional drift-diffusion models. Herein, we critically discuss the atomistic origin of the dynamic processes and the associated chemical disorder intrinsic to crystalline hybrid perovskite semiconductors. PMID:26859250

Highly sensitive ethanol chemical sensor based on Ni-doped SnO₂ nanostructure materials.

PubMed

Rahman, Mohammed M; Jamal, Aslam; Khan, Sher Bahadar; Faisal, M

2011-10-15

Due to potential applications of semiconductor transition doped nanostructure materials and the important advantages of synthesis in cost-effective and environmental concerns, a significant effort has been consummated for improvement of Ni-doped SnO(2) nanomaterials using hydrothermal technique at room conditions. The structural and optical properties of the low-dimensional (average diameter, 52.4 nm) Ni-doped SnO(2) nanostructures were demonstrated using various conventional techniques such as UV/visible spectroscopy, FT-IR spectroscopy, X-ray powder diffraction (XRD), and Field-emission scanning electron microscopy (FE-SEM). The calcined doped material is an attractive semiconductor nanoparticle for accomplishment in chemical sensing by simple I-V technique, where toxic chemical (ethanol) is used as a target chemical. Thin-film of Ni-doped SnO(2) nanostructure materials with conducting coating agents on silver electrodes (AgE, surface area, 0.0216 cm(2)) revealed higher sensitivity and repeatability. The calibration plot is linear (R, 0.8440) over the large dynamic range (1.0 nM-1.0 mM), where the sensitivity is approximately 2.3148 μA cm(-2) mM(-1) with a detection limit of 0.6 nM, based on signal/noise ratio in short response time. Consequently on the basis of the sensitive communication among structures, morphologies, and properties, it is exemplified that the morphologies and the optical characteristics can be extended to a large scale in doping nanomaterials and proficient chemical sensors applications. Copyright © 2011 Elsevier B.V. All rights reserved.

Morphology control, defect engineering and photoactivity tuning of ZnO crystals by graphene oxide--a unique 2D macromolecular surfactant.

PubMed

Pan, Xiaoyang; Yang, Min-Quan; Xu, Yi-Jun

2014-03-28

Zinc oxide (ZnO) nanostructured materials have received significant attention because of their unique physicochemical and electronic properties. In particular, the functional properties of ZnO are strongly dependent on its morphology and defect structure, particularly for a semiconductor ZnO-based photocatalyst. Here, we demonstrate a simple strategy for simultaneous morphology control, defect engineering and photoactivity tuning of semiconductor ZnO by utilizing the unique surfactant properties of graphene oxide (GO) in a liquid phase. By varying the amount of GO added during the synthesis process, the morphology of ZnO gradually evolves from a one dimensional prismatic rod to a hexagonal tube-like architecture while GO is converted into reduced GO (RGO). In addition, the introduction of GO can create oxygen vacancies in the lattice of ZnO crystals. As a result, the absorption edge of the wide band gap semiconductor ZnO is effectively extended to the visible light region, which thus endows the RGO-ZnO nanocomposites with visible light photoactivity; in contrast, the bare ZnO nanorod is only UV light photoactive. The synergistic integration of the unique morphology and the presence of oxygen vacancies imparts the RGO-ZnO nanocomposite with remarkably enhanced visible light photoactivity as compared to bare ZnO and its counterpart featuring different structural morphologies and the absence of oxygen vacancies. Our promising results highlight the versatility of the 2D GO as a solution-processable macromolecular surfactant to fabricate RGO-semiconductor nanocomposites with tunable morphology, defect structure and photocatalytic performance in a system-materials-engineering way.

Two dimensional thermal and charge mapping of power thyristors

NASA Technical Reports Server (NTRS)

Hu, S. P.; Rabinovici, B. M.

1975-01-01

The two dimensional static and dynamic current density distributions within the junction of semiconductor power switching devices and in particular the thyristors were obtained. A method for mapping the thermal profile of the device junctions with fine resolution using an infrared beam and measuring the attenuation through the device as a function of temperature were developed. The results obtained are useful in the design and quality control of high power semiconductor switching devices.

Excitonic effects in two-dimensional semiconductors: Path integral Monte Carlo approach

DOE PAGES

Velizhanin, Kirill A.; Saxena, Avadh

2015-11-01

The most striking features of novel two-dimensional semiconductors (e.g., transition metal dichalcogenide monolayers or phosphorene) is a strong Coulomb interaction between charge carriers resulting in large excitonic effects. In particular, this leads to the formation of multicarrier bound states upon photoexcitation (e.g., excitons, trions, and biexcitons), which could remain stable at near-room temperatures and contribute significantly to the optical properties of such materials. In our work we have used the path integral Monte Carlo methodology to numerically study properties of multicarrier bound states in two-dimensional semiconductors. Specifically, we have accurately investigated and tabulated the dependence of single-exciton, trion, and biexcitonmore » binding energies on the strength of dielectric screening, including the limiting cases of very strong and very weak screening. Our results of this work are potentially useful in the analysis of experimental data and benchmarking of theoretical and computational models.« less

A microprocessor based on a two-dimensional semiconductor.

PubMed

Wachter, Stefan; Polyushkin, Dmitry K; Bethge, Ole; Mueller, Thomas

2017-04-11

The advent of microcomputers in the 1970s has dramatically changed our society. Since then, microprocessors have been made almost exclusively from silicon, but the ever-increasing demand for higher integration density and speed, lower power consumption and better integrability with everyday goods has prompted the search for alternatives. Germanium and III-V compound semiconductors are being considered promising candidates for future high-performance processor generations and chips based on thin-film plastic technology or carbon nanotubes could allow for embedding electronic intelligence into arbitrary objects for the Internet-of-Things. Here, we present a 1-bit implementation of a microprocessor using a two-dimensional semiconductor-molybdenum disulfide. The device can execute user-defined programs stored in an external memory, perform logical operations and communicate with its periphery. Our 1-bit design is readily scalable to multi-bit data. The device consists of 115 transistors and constitutes the most complex circuitry so far made from a two-dimensional material.

A microprocessor based on a two-dimensional semiconductor

NASA Astrophysics Data System (ADS)

Wachter, Stefan; Polyushkin, Dmitry K.; Bethge, Ole; Mueller, Thomas

2017-04-01

The advent of microcomputers in the 1970s has dramatically changed our society. Since then, microprocessors have been made almost exclusively from silicon, but the ever-increasing demand for higher integration density and speed, lower power consumption and better integrability with everyday goods has prompted the search for alternatives. Germanium and III-V compound semiconductors are being considered promising candidates for future high-performance processor generations and chips based on thin-film plastic technology or carbon nanotubes could allow for embedding electronic intelligence into arbitrary objects for the Internet-of-Things. Here, we present a 1-bit implementation of a microprocessor using a two-dimensional semiconductor--molybdenum disulfide. The device can execute user-defined programs stored in an external memory, perform logical operations and communicate with its periphery. Our 1-bit design is readily scalable to multi-bit data. The device consists of 115 transistors and constitutes the most complex circuitry so far made from a two-dimensional material.

Heterostructured TiO2/NiTiO3 Nanorod Arrays for Inorganic Sensitized Solar Cells with Significantly Enhanced Photovoltaic Performance and Stability.

PubMed

Li, Yue-Ying; Wang, Jian-Gan; Sun, Huan-Huan; Wei, Bingqing

2018-04-11

Organic dyes used in the conventional dye-sensitized solar cells (DSSCs) suffer from poor light stability and high cost. In this work, we demonstrate a new inorganic sensitized solar cell based on ordered one-dimensional semiconductor nanorod arrays of TiO 2 /NiTiO 3 (NTO) heterostructures prepared via a facile two-step hydrothermal approach. The semiconductor heterostructure arrays are highly desirable and promising for DSSCs because of their direct charge transport capability and slow charge recombination rate. The low-cost NTO inorganic semiconductor possesses an appropriate band gap that matches well with TiO 2 , which behaves like a "dye" to enable efficient light harvesting and fast electron-hole separation. The solar cells constructed by the ordered TiO 2 /NTO heterostructure photoanodes show a significantly improved power conversion efficiency, high fill factor, and more promising, outstanding life stability. The present work will open up an avenue to design heterostructured inorganics for high-performance solar cells.

Novel drift structures for silicon and compound semiconductor X-ray and gamma-ray detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patt, B.E.; Iwanczyk, J.S.

Recently developed silicon- and compound-semiconductor-based drift detector structures have produced excellent performance for charged particles, X-rays, and gamma rays and for low-signal visible light detection. The silicon drift detector (SDD) structures that the authors discuss relate to direct X-ray detectors and scintillation photon detectors coupled with scintillators for gamma rays. Recent designs include several novel features that ensure very low dark current and hence low noise. In addition, application of thin window technology ensures a very high quantum efficiency entrance window on the drift photodetector. The main features of the silicon drift structures for X rays and light detection aremore » very small anode capacitance independent of the overall detector size, low noise, and high throughput. To take advantage of the small detector capacitance, the first stage of the electronics needs to be integrated into the detector anode. In the gamma-ray application, factors other than electronic noise dominate, and there is no need to integrate the electronics into the anode. Thus, a different drift structure is needed in conjunction with a high-Z material. The main features in this case are large active detector volume and electron-only induced signal.« less

Atom chips with free-standing two-dimensional electron gases: advantages and challenges

NASA Astrophysics Data System (ADS)

Sinuco-León, G. A.; Krüger, P.; Fromhold, T. M.

2018-03-01

In this work, we consider the advantages and challenges of using free-standing two-dimensional electron gases (2DEG) as active components in atom chips for manipulating ultracold ensembles of alkali atoms. We calculate trapping parameters achievable with typical high-mobility 2DEGs in an atom chip configuration and identify advantages of this system for trapping atoms at sub-micron distances from the atom chip. We show how the sensitivity of atomic gases to magnetic field inhomogeneity can be exploited for controlling the atoms with quantum electronic devices and, conversely, using the atoms to probe the structural and transport properties of semiconductor devices.

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection.

PubMed

Wibowo, Arief C; Malliakas, Christos D; Liu, Zhifu; Peters, John A; Sebastian, Maria; Chung, Duck Young; Wessels, Bruce W; Kanatzidis, Mercouri G

2013-06-17

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.

Spontaneous time reversal symmetry breaking in atomically confined two-dimensional impurity bands in silicon and germanium

NASA Astrophysics Data System (ADS)

Ghosh, Arindam

Three-dimensional bulk-doped semiconductors, in particular phosphorus (P)-doped silicon (Si) and germanium (Ge), are among the best studied systems for many fundamental concepts in solid state physics, ranging from the Anderson metal-insulator transition to the many-body Coulomb interaction effects on quantum transport. Recent advances in material engineering have led to vertically confined doping of phosphorus (P) atoms inside bulk crystalline silicon and germanium, where the electron transport occurs through one or very few atomic layers, constituting a new and unique platform to investigate many of these phenomena at reduced dimensions. In this talk I shall present results of extensive quantum transport experiments in delta-doped silicon and germanium epilayers, over a wide range of doping density that allow independent tuning of the on-site Coulomb interaction and hopping energy scales. We find that low-frequency flicker noise, or the 1 / f noise, in the electrical conductance of these systems is exceptionally low, and in fact among the lowest when compared with other low-dimensional materials. This is attributed to the physical separation of the conduction electrons, embedded inside the crystalline semiconductor matrix, from the charged fluctuators at the surface. Most importantly, we find a remarkable suppression of weak localization effects, including the quantum correction to conductivity and universal conductance fluctuations, with decreasing doping density or, equivalently, increasing effective on-site Coulomb interaction. In-plane magneto-transport measurements indicate the presence of intrinsic local spin fluctuations at low doping although no signatures of long range magnetic order could be identified. We argue that these results indicate a spontaneous breakdown of time reversal symmetry, which is one of the most fundamental and robust symmetries of nonmagnetic quantum systems. While the microscopic origin of this spontaneous time reversal symmetry breaking remains unknown, we believe this indicates a new many-body electronic phase in two-dimensionally doped silicon and germanium with a half-filled impurity band. We acknowledge financial support from Department of Science and Technology, Government of India, and Australia-India Strategic Research Fund (AISRF).

Exchange Enhancement of the Electron-Phonon Interaction: The Case of Weakly Doped Two-Dimensional Multivalley Semiconductors

NASA Astrophysics Data System (ADS)

Pamuk, Betül; Zoccante, Paolo; Baima, Jacopo; Mauri, Francesco; Calandra, Matteo

2018-04-01

The effect of the exchange interaction on the vibrational properties and on the electron-phonon coupling were investigated in several recent works. In most of the cases, exchange tends to enhance the electron-phonon interaction, although the motivations for such behaviour are not completely understood. Here we consider the class of weakly doped two-dimensional multivalley semiconductors and we demonstrate that a more global picture emerges. In particular we show that in these systems, at low enough doping, even a moderate electron-electron interaction enhances the response to any perturbation inducing a valley polarization. If the valley polarization is due to the electron-phonon coupling, the electron-electron interaction results in an enhancement of the superconducting critical temperature. We demonstrate the applicability of the theory by performing random phase approximation and first principles calculations in transition metal chloronitrides. We find that exchange is responsible for the enhancement of the superconducting critical temperature in LixZrNCl and that much larger Tcs could be obtained in intercalated HfNCl if the synthesis of cleaner samples could remove the Anderson insulating state competing with superconductivity.

Determination of layer-dependent exciton binding energies in few-layer black phosphorus

PubMed Central

Zhang, Guowei; Chaves, Andrey; Huang, Shenyang; Wang, Fanjie; Xing, Qiaoxia; Low, Tony; Yan, Hugen

2018-01-01

The attraction between electrons and holes in semiconductors forms excitons, which largely determine the optical properties of the hosting material, and hence the device performance, especially for low-dimensional systems. Mono- and few-layer black phosphorus (BP) are emerging two-dimensional (2D) semiconductors. Despite its fundamental importance and technological interest, experimental investigation of exciton physics has been rather limited. We report the first systematic measurement of exciton binding energies in ultrahigh-quality few-layer BP by infrared absorption spectroscopy, with layer (L) thickness ranging from 2 to 6 layers. Our experiments allow us to determine the exciton binding energy, decreasing from 213 meV (2L) to 106 meV (6L). The scaling behavior with layer numbers can be well described by an analytical model, which takes into account the nonlocal screening effect. Extrapolation to free-standing monolayer yields a large binding energy of ~800 meV. Our study provides insights into 2D excitons and their crossover from 2D to 3D, and demonstrates that few-layer BP is a promising high-quality optoelectronic material for potential infrared applications. PMID:29556530

Quantifying resistances across nanoscale low- and high-angle interspherulite boundaries in solution-processed organic semiconductor thin films.

PubMed

Lee, Stephanie S; Mativetsky, Jeffrey M; Loth, Marsha A; Anthony, John E; Loo, Yueh-Lin

2012-11-27

The nanoscale boundaries formed when neighboring spherulites impinge in polycrystalline, solution-processed organic semiconductor thin films act as bottlenecks to charge transport, significantly reducing organic thin-film transistor mobility in devices comprising spherulitic thin films as the active layers. These interspherulite boundaries (ISBs) are structurally complex, with varying angles of molecular orientation mismatch along their lengths. We have successfully engineered exclusively low- and exclusively high-angle ISBs to elucidate how the angle of molecular orientation mismatch at ISBs affects their resistivities in triethylsilylethynyl anthradithiophene thin films. Conductive AFM and four-probe measurements reveal that current flow is unaffected by the presence of low-angle ISBs, whereas current flow is significantly disrupted across high-angle ISBs. In the latter case, we estimate the resistivity to be 22 MΩμm(2)/width of the ISB, only less than a quarter of the resistivity measured across low-angle grain boundaries in thermally evaporated sexithiophene thin films. This discrepancy in resistivities across ISBs in solution-processed organic semiconductor thin films and grain boundaries in thermally evaporated organic semiconductor thin films likely arises from inherent differences in the nature of film formation in the respective systems.

Characterization of metal-ferroelectric-insulator-semiconductor structures based on ferroelectric Langmuir-Blodgett polyvinylidene fluoride copolymer films for nondestructive random access memory applications

NASA Astrophysics Data System (ADS)

Reece, Timothy James

Ferroelectric field effect transistors (FeFETs) have attracted much attention recently because of their ability to combine high speed, low power consumption, and fast nondestructive readout with the potential for high density nonvolatile memory. The polarization of the ferroelectric is used to switch the channel at the silicon surface between states of high and low conductance. Among the ferroelectric thin films used in FET devices; the ferroelectric copolymer of Polyvinylidene fluoride, PVDF (C2H2F 2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, low cost and compatibility with organic semiconductors. By employing the Langmuir-Blodgett technique, films as thin as 1.8 nm can be deposited, reducing the operating voltage. An MFIS structure consisting of aluminum, 170 nm P(VDF-TrFE), 100 nm silicon oxide and n-type silicon exhibited low leakage current (˜1x10 -8 A/cm2), a large memory window (4.2 V) and operated at 35 Volts. The operating voltage was lowered through use of high k insulators like cerium oxide. A sample consisting of 25 nm P(VDF-TrFE), 30 nm cerium oxide and p-type silicon exhibited a 1.9 V window with 7 Volt gate amplitude. The leakage current in this case was considerably higher (1x10 -6 A/cm2). The characterization, modeling, and fabrication of metal-ferroelectricinsulator semiconductor (MFIS) structures based on these films are discussed.

Low-Temperature Synthesis of New Ternary Chalcogenide Compounds of Copper, Gold, and Mercury Using Alkali Metal Polychalcogenide Fluxes

NASA Astrophysics Data System (ADS)

Park, Younbong

In last two decades great efforts have been exerted to find new materials with interesting optical, electrical, and catalytic properties. Metal chalcogenides have been studied extensively because of their interesting physical properties and rich structural chemistry, among the potential materials. Prior to this work, most known metal chalcogenides had been synthesized at high temperature (T > 500^circC). Intermediate temperature synthesis in solid state chemistry was seldom pursued because of the extremely slow diffusion rates between reactants. This intermediate temperature regime could be a new synthesis condition if one looks for new materials with unusual structural features and properties. Metastable or kinetically stable compounds can be stabilized in this intermediate temperature regime, in contrast to the thermodynamically stable high temperature compounds. Molten salts, especially alkali metal polychalcogenide fluxes, can provide a route for exploring new chalcogenide materials at intermediate temperatures. These fluxes are very reactive and melt as low as 145^circC (mp of K_2S_4). Using these fluxes as reaction media, we have encountered many novel chalcogenide compounds with unusual structures and interesting electrical properties (semiconductors to metallic conductors). Low-dimensional polychalcogenide compounds of alpha-ACuQ_4 (A = K, Cs; Q = S, Se), beta -KCuS_4, KAuQ_5 (Q = S, Se), K_3AuSe_ {13}, Na_3AuSe _8, and CsAuSe_3 exhibit the beautiful structural diversity and bonding flexibility of the polychalcogenide ligands. In addition, many novel chalcogenide compounds of Cu, Hg, and Au with low-dimensional structures. The preparation of novel mixed -valence Cu compounds, K_2Cu _5Te_5, Cs _3Cu_8Te_ {10}, Na_3Cu _4Se_4, K _3Cu_8S_4 Te_2, and KCu_4 S_2Te, which show interesting metallic properties, especially underscores the enormous potential of the molten salt method for the synthesis of new chalcogenide materials with interesting physical properties. The materials prepared in this study can be classified as a new class of chalcogenide compounds due to their unique structures. In this dissertation the synthesis, characterization with emphasis on structures, charge transport properties, and magnetic susceptibilities of the materials will be illustrated.

Effect of alkali cations on two-dimensional networks of two new quaternary thioarsenates (III) prepared by a facile surfactant-thermal method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Dongming; Hou, Peipei; Liu, Chang

2016-09-15

Two new quaternary thioarsenates(III) NaAg{sub 2}AsS{sub 3}·H{sub 2}O (1) and KAg{sub 2}AsS{sub 3} (2) with high yields have been successfully prepared through a facile surfactant-thermal method. It is interesting that 2 can only be obtained with the aid of ethanediamine (en), which indicates that weak basicity of solvent is beneficial to the growth of 2 compared with 1. Both 1 and 2 feature the similar two-dimensional (2D) layer structures. However, the distortion of the primary honeycomb-like nets in 2 is more severe than that of 1, which demonstrates that Na{sup +} and K{sup +} cations have different structure directing effectsmore » on these two thioarsenates(III). Both experimental and theoretical studies confirm 1 and 2 are semiconductors with band gaps in the visible region. Our success in preparing these two quaternary thioarsenates(III) proves that surfactant-thermal technique is a powerful yet facile synthetic method to explore new complex chalcogenides. - Graphical abstract: Two new quaternary thioarsenates(III) NaAg{sub 2}AsS{sub 3}·H{sub 2}O (1) and KAg{sub 2}AsS{sub 3} (2) with high yields have been successfully prepared through a facile surfactant-thermal method. X-ray single crystal diffraction analyses demonstrate that Na{sup +} and K{sup +} cations have different structure directing effects on these two thioarsenates(III). Both experimental and theoretical studies confirm 1 and 2 are semiconductors with band gaps in the visible region. Display Omitted - Highlights: • NaAg{sub 2}AsS{sub 3}⋅H{sub 2}O (1) and KAg{sub 2}AsS{sub 3} (2) were prepared through surfactant-thermal method. • Crystal structures show Na{sup ±} and K{sup ±} have different structure directing effects. • The weak basicity of solvent is benefit to the growth of 2 compared with 1. • Experimental and theoretical studies confirm 1 and 2 are semiconductors.« less

Improved integration of ultra-thin high-k dielectrics in few-layer MoS2 FET by remote forming gas plasma pretreatment

NASA Astrophysics Data System (ADS)

Wang, Xiao; Zhang, Tian-Bao; Yang, Wen; Zhu, Hao; Chen, Lin; Sun, Qing-Qing; Zhang, David Wei

2017-01-01

The effective and high-quality integration of high-k dielectrics on two-dimensional (2D) crystals is essential to the device structure engineering and performance improvement of field-effect transistor (FET) based on the 2D semiconductors. We report a 2D MoS2 transistor with ultra-thin Al2O3 top-gate dielectric (6.1 nm) and extremely low leakage current. Remote forming gas plasma pretreatment was carried out prior to the atomic layer deposition, providing nucleation sites with the physically adsorbed ions on the MoS2 surface. The top gate MoS2 FET exhibited excellent electrical performance, including high on/off current ratio over 109, subthreshold swing of 85 mV/decade and field-effect mobility of 45.03 cm2/V s. Top gate leakage current less than 0.08 pA/μm2 at 4 MV/cm has been obtained, which is the smallest compared with the reported top-gated MoS2 transistors. Such an optimized integration of high-k dielectric in 2D semiconductor FET with enhanced performance is very attractive, and it paves the way towards the realization of more advanced 2D nanoelectronic devices and integrated circuits.

Carbon kagome lattice and orbital-frustration-induced metal-insulator transition for optoelectronics.

PubMed

Chen, Yuanping; Sun, Y Y; Wang, H; West, D; Xie, Yuee; Zhong, J; Meunier, V; Cohen, Marvin L; Zhang, S B

2014-08-22

A three-dimensional elemental carbon kagome lattice, made of only fourfold-coordinated carbon atoms, is proposed based on first-principles calculations. Despite the existence of 60° bond angles in the triangle rings, widely perceived to be energetically unfavorable, the carbon kagome lattice is found to display exceptional stability comparable to that of C(60). The system allows us to study the effects of triangular frustration on the electronic properties of realistic solids, and it demonstrates a metal-insulator transition from that of graphene to a direct gap semiconductor in the visible blue region. By minimizing s-p orbital hybridization, which is an intrinsic property of carbon, not only the band edge states become nearly purely frustrated p states, but also the band structure is qualitatively different from any known bulk elemental semiconductors. For example, the optical properties are similar to those of direct-gap semiconductors GaN and ZnO, whereas the effective masses are comparable to or smaller than those of Si.

On the Charge transport regime of crystalline organic semiconductors: diffusion limited by thermal off-diagonal electronic disorder

NASA Astrophysics Data System (ADS)

Troisi, Alessandro

2006-03-01

In organic crystalline semiconductor molecular components are held together by very weak interactions and the transfer integrals between neighboring molecular orbitals are extremely sensitive to small nuclear displacements. We used a mixed quantum chemical and molecular dynamic methodology to assess the effect of thermal structural fluctuations on the modulation of the transfer integrals between close molecules. We have found that the fluctuations of the transfer integrals are of the same order of magnitude of their average value for pentacene and anthracene. This condition makes the band description inadequate because a dynamic localization takes place and the translational symmetry is completely broken for the electronic states. We also present a simple one-dimensional semiclassical model that incorporates the effects of dynamical localization and allows the numerical computation of the charge mobility for ordered organic semiconductors. These results explain several contrasting experimental observations pointing sometimes to a delocalized ``band-like'' transport and sometimes to the existence of strongly localized charge carriers.

Analysis of electric field distribution in GaAs metal-semiconductor field effect transistor with a field-modulating plate

NASA Astrophysics Data System (ADS)

Hori, Yasuko; Kuzuhara, Masaaki; Ando, Yuji; Mizuta, Masashi

2000-04-01

Electric field distribution in the channel of a field effect transistor (FET) with a field-modulating plate (FP) has been theoretically investigated using a two-dimensional ensemble Monte Carlo simulation. This analysis revealed that the introduction of FP is effective in canceling the influence of surface traps under forward bias conditions and in reducing the electric field intensity at the drain side of the gate edge under pinch-off bias conditions. This study also found that a partial overlap of the high-field region under the gate and that at the FP electrode is important for reducing the electric field intensity. The optimized metal-semiconductor FET with FP (FPFET) (LGF˜0.2 μm) exhibited a much lower peak electric field intensity than a conventional metal-semiconductor FET. Based on these numerically calculated results, we have proposed a design procedure to optimize the power FPFET structure with extremely high breakdown voltages while maintaining reasonable gain performance.

Improvement of Surge Protection by Using an AlGaN/GaN-Based Metal-Semiconductor-Metal Two-Dimensional Electron Gas Varactor

NASA Astrophysics Data System (ADS)

Ferng, Yi-Cherng; Chang, Liann-Be; Das, Atanu; Lin, Ching-Chi; Cheng, Chun-Yu; Kuei, Ping-Yu; Chow, Lee

2012-12-01

In this paper, a varactor with metal-semiconductor-metal diodes on top of the (NH4)2S/P2S5-treated AlGaN/GaN two-dimensional electron gas epitaxial structure (MSM-2DEG) is proposed to the surge protection for the first time. The sulfur-treated MSM-2DEG varactor properties, including current-voltage (I-V), capacitance-voltage (C-V), and frequency response of the proposed surge protection circuit, are presented. To verify its capability of surge protection, we replace the metal oxide varistor (MOV) and resistor (R) in a state-of-the-art surge protection circuit with the sulfur-treated MSM-2DEG varactor under the application conditions of system-level surge tests. The measured results show that the proposed surge protection circuit, consisted of a gas discharge arrester (GDA) and a sulfur-treated MSM-2DEG varactor, can suppress an electromagnetic pulse (EMP) voltage of 4000 to 360 V, a reduction of 91%, whereas suppression is to 1780 V, a reduction of 55%, when using only a GDA.

Analysing black phosphorus transistors using an analytic Schottky barrier MOSFET model.

PubMed

Penumatcha, Ashish V; Salazar, Ramon B; Appenzeller, Joerg

2015-11-13

Owing to the difficulties associated with substitutional doping of low-dimensional nanomaterials, most field-effect transistors built from carbon nanotubes, two-dimensional crystals and other low-dimensional channels are Schottky barrier MOSFETs (metal-oxide-semiconductor field-effect transistors). The transmission through a Schottky barrier-MOSFET is dominated by the gate-dependent transmission through the Schottky barriers at the metal-to-channel interfaces. This makes the use of conventional transistor models highly inappropriate and has lead researchers in the past frequently to extract incorrect intrinsic properties, for example, mobility, for many novel nanomaterials. Here we propose a simple modelling approach to quantitatively describe the transfer characteristics of Schottky barrier-MOSFETs from ultra-thin body materials accurately in the device off-state. In particular, after validating the model through the analysis of a set of ultra-thin silicon field-effect transistor data, we have successfully applied our approach to extract Schottky barrier heights for electrons and holes in black phosphorus devices for a large range of body thicknesses.

Analysing black phosphorus transistors using an analytic Schottky barrier MOSFET model

PubMed Central

Penumatcha, Ashish V.; Salazar, Ramon B.; Appenzeller, Joerg

2015-01-01

Owing to the difficulties associated with substitutional doping of low-dimensional nanomaterials, most field-effect transistors built from carbon nanotubes, two-dimensional crystals and other low-dimensional channels are Schottky barrier MOSFETs (metal-oxide-semiconductor field-effect transistors). The transmission through a Schottky barrier-MOSFET is dominated by the gate-dependent transmission through the Schottky barriers at the metal-to-channel interfaces. This makes the use of conventional transistor models highly inappropriate and has lead researchers in the past frequently to extract incorrect intrinsic properties, for example, mobility, for many novel nanomaterials. Here we propose a simple modelling approach to quantitatively describe the transfer characteristics of Schottky barrier-MOSFETs from ultra-thin body materials accurately in the device off-state. In particular, after validating the model through the analysis of a set of ultra-thin silicon field-effect transistor data, we have successfully applied our approach to extract Schottky barrier heights for electrons and holes in black phosphorus devices for a large range of body thicknesses. PMID:26563458

Internal optical bistability of quasi-two-dimensional semiconductor nanoheterostructures

NASA Astrophysics Data System (ADS)

Derevyanchuk, Oleksandr V.; Kramar, Natalia K.; Kramar, Valeriy M.

2018-01-01

We represent the results of numerical computations of the frequency and temperature domains of possible realization of internal optical bistability in flat quasi-two-dimensional semiconductor nanoheterostructures with a single quantum well (i.e., nanofilms). Particular computations have been made for a nanofilm of layered semiconductor PbI2 embedded in dielectric medium, i.e. ethylene-methacrylic acid (E-MAA) copolymer. It is shown that an increase in the nanofilm's thickness leads to a long-wave shift of the frequency range of the manifestation the phenomenon of bistability, to increase the size of the hysteresis loop, as well as to the expansion of the temperature interval at which the realization of this phenomenon is possible.

Design and Analysis of CMOS-Compatible III-V Compound Electron-Hole Bilayer Tunneling Field-Effect Transistor for Ultra-Low-Power Applications.

PubMed

Kim, Sung Yoon; Seo, Jae Hwa; Yoon, Young Jun; Lee, Ho-Young; Lee, Seong Min; Cho, Seongjae; Kang, In Man

2015-10-01

In this work, we design and analyze complementary metal-oxide-semiconductor (CMOS)-compatible III-V compound electron-hole bilayer (EHB) tunneling field-effect transistors (TFETs) by using two-dimensional (2D) technology computer-aided design (TCAD) simulations. A recently proposed EHB TFET exploits a bias-induced band-to-band tunneling (BTBT) across the electron-hole bilayer by an electric field from the top and bottom gates. This is in contrast to conventional planar p(+)-p(-)-n TFETs, which utilize BTBT across the source-to-channel junction. We applied III-V compound semiconductor materials to the EHB TFETs in order to enhance the current drivability and switching performance. Devices based on various compound semiconductor materials have been designed and analyzed in terms of their primary DC characteristics. In addition, the operational principles were validated by close examination of the electron concentrations and energy-band diagrams under various operation conditions. The simulation results of the optimally designed In0.533Ga0.47As EHB TFET show outstanding performance, with an on-state current (Ion) of 249.5 μA/μm, subthreshold swing (S) of 11.4 mV/dec, and threshold voltage (Vth) of 50 mV at VDS = 0.5 V. Based on the DC-optimized InGaAs EHB TFET, the CMOS inverter circuit was simulated in views of static and dynamic behaviors of the p-channel device with exchanges between top and bottom gates or between source and drain electrodes maintaining the device structure.

Shift of semimetal-semiconductor bond direction on “0 1 1” to “1 1 1” Bismuth quazi-two-dimension system

NASA Astrophysics Data System (ADS)

Yazdani, Ahmad; Hamreh, Sajad

2018-03-01

The electronic structure of the nanocrystallines and quasi-two-dimensional systems strongly impressed by the thermodynamic- behavior mainly due to excess of hidden surface free energy. Therefore, the stability of crystalline structure’s change could be related to band-offset of bond rupturing of atomic displacements. whereas for the electronic-structure of "Bi" it seams the competition of L.S and bond exchange should be effectively dominated. Besides all of the characters behave spatial like strong sensitive oxidation here it is supposed that strong correlated electronic structure in the absence of oxygen is resulted on direction of redistribution of surface chemical bond formation before any reconstructive structure. Where • The metallic direction of electronic structure “0 1 1” is changed to “1 1 1” semiconductor direction. • the effect of L.S is more evident on the local density of state while it is not observable around the fermi level. • Strong effect of spin-orbit interaction on splitting of the valance to nearly conduction band around the fermi level is more evident.

Charge-transfer channel in quantum dot-graphene hybrid materials

NASA Astrophysics Data System (ADS)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Charge-transfer channel in quantum dot-graphene hybrid materials.

PubMed

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-06

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd 13 Se 13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces.

PubMed

Corfdir, Pierre; Li, Hong; Marquardt, Oliver; Gao, Guanhui; Molas, Maciej R; Zettler, Johannes K; van Treeck, David; Flissikowski, Timur; Potemski, Marek; Draxl, Claudia; Trampert, Achim; Fernández-Garrido, Sergio; Grahn, Holger T; Brandt, Oliver

2018-01-10

In semiconductor quantum-wire heterostructures, interface roughness leads to exciton localization and to a radiative decay rate much smaller than that expected for structures with flat interfaces. Here, we uncover the electronic and optical properties of the one-dimensional extended defects that form at the intersection between stacking faults and inversion domain boundaries in GaN nanowires. We show that they act as crystal-phase quantum wires, a novel one-dimensional quantum system with atomically flat interfaces. These quantum wires efficiently capture excitons whose radiative decay gives rise to an optical doublet at 3.36 eV at 4.2 K. The binding energy of excitons confined in crystal-phase quantum wires is measured to be more than twice larger than that of the bulk. As a result of their unprecedented interface quality, these crystal-phase quantum wires constitute a model system for the study of one-dimensional excitons.

Semi-metallic Be5C2 monolayer global minimum with quasi-planar pentacoordinate carbons and negative Poisson's ratio.

PubMed

Wang, Yu; Li, Feng; Li, Yafei; Chen, Zhongfang

2016-05-03

Designing new materials with novel topological properties and reduced dimensionality is always desirable for material innovation. Here we report the design of a two-dimensional material, namely Be5C2 monolayer on the basis of density functional theory computations. In Be5C2 monolayer, each carbon atom binds with five beryllium atoms in almost the same plane, forming a quasi-planar pentacoordinate carbon moiety. Be5C2 monolayer appears to have good stability as revealed by its moderate cohesive energy, positive phonon modes and high melting point. It is the lowest-energy structure with the Be5C2 stoichiometry in two-dimensional space and therefore holds some promise to be realized experimentally. Be5C2 monolayer is a gapless semiconductor with a Dirac-like point in the band structure and also has an unusual negative Poisson's ratio. If synthesized, Be5C2 monolayer may find applications in electronics and mechanics.

A new series of two-dimensional silicon crystals with versatile electronic properties

NASA Astrophysics Data System (ADS)

Chae, Kisung; Kim, Duck Young; Son, Young-Woo

2018-04-01

Silicon (Si) is one of the most extensively studied materials owing to its significance to semiconductor science and technology. While efforts to find a new three-dimensional (3D) Si crystal with unusual properties have made some progress, its two-dimensional (2D) phases have not yet been explored as much. Here, based on a newly developed systematic ab initio materials searching strategy, we report a series of novel 2D Si crystals with unprecedented structural and electronic properties. The new structures exhibit perfectly planar outermost surface layers of a distorted hexagonal network with their thicknesses varying with the atomic arrangement inside. Dramatic changes in electronic properties ranging from semimetal to semiconducting with indirect energy gaps and even to one with direct energy gaps are realized by varying thickness as well as by surface oxidation. Our predicted 2D Si crystals with flat surfaces and tunable electronic properties will shed light on the development of silicon-based 2D electronics technology.

Artificially Structured Semiconductors to Model Novel Quantum Phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinczuk, Aron; Wind, Shalom J.

Award Period: September 1st, 2013 through February 15th, 2017 Submitted to the USDOE Office of Basic Energy Sciences By Aron Pinczuk and Shalom J. Wind Department of Applied Physics and Applied Mathematics Columbia University New York, NY 10027 January 2017 Award # DE-SC0010695 ABSTRACT Research in this project seeks to design, create and study a class of tunable artificial quantum structures in order to extend the range and scope of new and exciting physical phenomena and to explore the potential for new applications. Advanced nanofabrication was used to create an external potential landscape that acts as a lattice of confinementmore » sites for electrons (and/or holes) in a two-dimensional electron gas in a high perfection semiconductor in such a manner that quantum interactions between different sites dictate the significant physics. Our current focus is on ‘artificial graphene’ (AG) in which a set of quantum dots (or sites) are patterned in a honeycomb lattice. The combination of leading edge nanofabrication with ultra-pure semiconductor materials in this project extends the frontier for small period, low-disorder AG systems, enabling the exploration of graphene physics in a semiconductor platform. TECHNICAL DESCRIPTION Contemporary condensed matter science has entered an era of discovery of new low-dimensional materials, such as graphene and other atomically thin materials, that exhibit exciting new physical phenomena that were previously inaccessible. Concurrent with the discovery and development of these new materials are impressive advancements in nanofabrication, which offer an ever-expanding toolbox for creating a myriad of high quality patterns at nanoscale dimensions. This project started about four years ago. Among its major achievements are the realizations of very small period artificial lattices with honeycomb topology in GaAs quantum wells. In our most recent work the periods of the ‘artificial graphene’ (AG) lattices extend down to 40 nm. These small periods are about three times smaller than previously reported in GaAs quantum wells. This milestone establishes a new state-of-the-art in fields of research and nanofabrication. In experiments using optical scattering methods we uncovered evidence that free electrons in the small period AG lattices display novel features that arise from the symmetry of the honeycomb lattice. These achievements create semiconductor platforms for explorations of novel states and effects that offer opportunities to create quasiparticles with tunable character. The quest for the discovery of novel quantum physics by nanofabrication of ‘artificial structures’ in semiconductor quantum structures overlaps with the development of quantum simulators. Nanopatterns were created at Columbia University by the group of co-PI Shalom Wind using a 100keV e-beam nanolithography instrument (along with associated processing) that is part of the Columbia Nano Initiative. Optical experiments were carried out in the group of PI Aron Pinczuk. GaAs/AlGaAs quantum wells(QWs) of world-class perfection that serve as electron hosts are the starting material grown by molecular beam epitaxy (MBE) by our partners Dr. Loren Pfeiffer (Princeton Univ.) and Prof. Michael Manfra (Purdue Univ.). The inductively coupled plasma reactive ion etching (ICP-RIE) was carried out at the PRISM Micro/Nano Fabrication Laboratory of Princeton University. Dr. Vittorio Pellegrini (Istituto Italiano di Tecnologia, Genoa, Italy) has contributed critical insight on this research. Two graduate students in this project Sheng Wang and Diego Scarabelli, graduated in the summer/fall of 2016. Dr. Yuliya Kuznetsova has been a postdoc in the group. The current work is led by Dr. Lingjie Du, a postdoctoral scientist that joined the group of the PI on October 15th, 2016. Since the start of this project we have focused primarily on developing protocols towards the fabrication of the artificial lattices and in the implementation of characterization methods to identify the new electron states that are created. A major milestone has been the realization of the Dirac cones that emerge in honeycomb lattices. In the next phases of this project, and as we achieve milestones, we wish to expand our experimental platform so that we will be better positioned to access emergent novel quantum behavior and phases of electrons in artificial lattices designed and fabricated with ‘exquisite’ precision. The AG lattices with greatly reduced disorder from nano-processing that we have already created demonstrate that we are poised for the next stage exploration of graphene physics and applications in semiconductor quantum structures.« less

Hydrodynamic pumping of a quantum Fermi liquid in a semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Kantha, D.; Chen, H.; Govorov, A. O.

2003-03-01

We present experimental results for a pumping mechanism observed in mesoscopic structures patterned on two-dimensional electron systems in GaAs/AlGaAs heterostructures. The experiments are performed at low temperatures, in the ballistic regime. The effect is observed as a voltage or current signal corresponding to carrier extraction from sub-micron sized apertures, when these apertures are swept by a beam of ballistic electrons. The carrier extraction, phenomenologically reminiscent of the Bernoulli pumping effect in classical fluids, has been observed in various geometries. We ascertained linearity between measured voltage and injected current in all experiments, thereby excluding rectification effects. The linear response, however, points to a fundamental difference from the Bernoulli effect in classical liquids, where the response is nonlinear and quadratic in terms of the velocity. The temperature dependence of the effect will also be presented. We thank M. Shayegan (Princeton University) for the heterostructure growth, and acknowledge support from NSF DMR-0094055.

Two-dimensional tantalum disulfide: controlling structure and properties via synthesis

NASA Astrophysics Data System (ADS)

Zhao, Rui; Grisafe, Benjamin; Krishna Ghosh, Ram; Holoviak, Stephen; Wang, Baoming; Wang, Ke; Briggs, Natalie; Haque, Aman; Datta, Suman; Robinson, Joshua

2018-04-01

Tantalum disulfide (TaS2) is a transition metal dichalcogenide (TMD) that exhibits phase transition induced electronic property modulation at low temperature. However, the appropriate phase must be grown to enable the semiconductor/metal transition that is of interest for next generation electronic applications. In this work, we demonstrate direct and controllable synthesis of ultra-thin 1T-TaS2 and 2H-TaS2 on a variety of substrates (sapphire, SiO2/Si, and graphene) via powder vapor deposition. The synthesis process leads to single crystal domains ranging from 20 to 200 nm thick and 1-10 µm on a side. The TaS2 phase (1T or 2H) is controlled by synthesis temperature, which subsequently is shown to control the electronic properties. Furthermore, this work constitutes the first demonstration of a metal-insulator phase transition in directly synthesized 1T-TaS2 films and domains by electronic means.

Identification of strained black phosphorous by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Wan, Jiawei; Guo, Junhong; Hu, Fangren

2017-04-01

Phosphorene has a very high hole mobility and can be a tuned band structure, and has become an ideal material for electronic devices. For this new type of two-dimensional material, in the applied strain, black phosphorus (BP) can be changed into an indirect band gap and metallic materials from the direct band gap semiconductor material, which greatly affect its inherent physical characteristics. How to identify strained microstructure changes becomes an important problem. The calculated Raman spectra disclose that the A{}{{g}}2 mode and B{}2{{g}} mode will split and the Raman spectra appear, while the A{}{{g}}1 mode is shifted to low-frequency region. The deformation induced by strain will effectively change the Raman mode position and intensity, this can be used to identify phosphorus changes. Project supported by the National Science Foundation of China (Nos. 61505085, 61574080, 61274127) and the Innovation Project of Jiangsu Graduate Student, China (No. SJLX15_0379).

Carbon Nanotube Flexible and Stretchable Electronics

NASA Astrophysics Data System (ADS)

Cai, Le; Wang, Chuan

2015-08-01

The low-cost and large-area manufacturing of flexible and stretchable electronics using printing processes could radically change people's perspectives on electronics and substantially expand the spectrum of potential applications. Examples range from personalized wearable electronics to large-area smart wallpapers and from interactive bio-inspired robots to implantable health/medical apparatus. Owing to its one-dimensional structure and superior electrical property, carbon nanotube is one of the most promising material platforms for flexible and stretchable electronics. Here in this paper, we review the recent progress in this field. Applications of single-wall carbon nanotube networks as channel semiconductor in flexible thin-film transistors and integrated circuits, as stretchable conductors in various sensors, and as channel material in stretchable transistors will be discussed. Lastly, state-of-the-art advancement on printing process, which is ideal for large-scale fabrication of flexible and stretchable electronics, will also be reviewed in detail.

Carbon Nanotube Flexible and Stretchable Electronics.

PubMed

Cai, Le; Wang, Chuan

2015-12-01

The low-cost and large-area manufacturing of flexible and stretchable electronics using printing processes could radically change people's perspectives on electronics and substantially expand the spectrum of potential applications. Examples range from personalized wearable electronics to large-area smart wallpapers and from interactive bio-inspired robots to implantable health/medical apparatus. Owing to its one-dimensional structure and superior electrical property, carbon nanotube is one of the most promising material platforms for flexible and stretchable electronics. Here in this paper, we review the recent progress in this field. Applications of single-wall carbon nanotube networks as channel semiconductor in flexible thin-film transistors and integrated circuits, as stretchable conductors in various sensors, and as channel material in stretchable transistors will be discussed. Lastly, state-of-the-art advancement on printing process, which is ideal for large-scale fabrication of flexible and stretchable electronics, will also be reviewed in detail.

Seebeck coefficient of synthesized Titanium Dioxide thin film on FTO glass substrate

NASA Astrophysics Data System (ADS)

Usop, R.; Hamed, N. K. A.; Megat Hasnan, M. M. I.; Ikeda, H.; Sabri, M. F. M.; Ahmad, M. K.; Said, S. M.; Salleh, F.

2018-04-01

In order to fabricate a thermoelectric device on glass substrate for harvesting waste heat energy through house appliances, the Seebeck coefficient of translucent TiO2 thin film was investigated. The TiO2 thin film was synthesized by using hydrothermal method with F-SnO2 coated glass as substrate. From scanning electron microscopy analysis, the synthesized TiO2 thin film was found to be in nanometer-scale rod structure with a thickness of 4 µm. The Seebeck coefficient was measured in the temperature range of 300 – 400 K. The Seebeck coefficient is found to be in negative value which shows that synthesized film is an n-type semiconductor material, and is lower than the value of bulk-size material. This reduction in Seebeck coefficient of TiO2 thin film is likely due to the low dimensional effect and the difference of carrier concentration.

Ultralow-frequency collective compression mode and strong interlayer coupling in multilayer black phosphorus

DOE PAGES

Dong, Shan; Zhang, Anmin; Liu, Kai; ...

2016-02-26

The recent renaissance of black phosphorus (BP) as a two-dimensional (2D) layered material has generated tremendous interest, but its unique structural characters underlying many of its outstanding properties still need elucidation. Here we report Raman measurements that reveal an ultralow-frequency collective compression mode (CCM) in BP, which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling, and this result is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of themore » thickness up to tens of atomic layers, which is considerably higher than previously achieved by using high-frequency Raman modes. Lastly, these findings offer fundamental insights and practical tools for further exploration of BP as a highly promising new 2D semiconductor.« less

Exploration of operator method digital optical computers for application to NASA

NASA Technical Reports Server (NTRS)

1990-01-01

Digital optical computer design has been focused primarily towards parallel (single point-to-point interconnection) implementation. This architecture is compared to currently developing VHSIC systems. Using demonstrated multichannel acousto-optic devices, a figure of merit can be formulated. The focus is on a figure of merit termed Gate Interconnect Bandwidth Product (GIBP). Conventional parallel optical digital computer architecture demonstrates only marginal competitiveness at best when compared to projected semiconductor implements. Global, analog global, quasi-digital, and full digital interconnects are briefly examined as alternative to parallel digital computer architecture. Digital optical computing is becoming a very tough competitor to semiconductor technology since it can support a very high degree of three dimensional interconnect density and high degrees of Fan-In without capacitive loading effects at very low power consumption levels.

III-V semiconductor nanoresonators-a new strategy for passive, active, and nonlinear all-dielectric metamaterials

DOE PAGES

Liu, Sheng; Keeler, Gordon A.; Reno, John L.; ...

2016-06-10

We demonstrate 2D and multilayer dielectric metamaterials made from III–V semiconductors using a monolithic fabrication process. The resulting structures could be used to recompress chirped femtosecond optical pulses and in a variety of other optical applications requiring low loss. Moreover, these III–V all-dielectric metamaterials could enable novel active applications such as efficient nonlinear frequency converters, light emitters, detectors, and modulators.

Breaking the GaN material limits with nanoscale vertical polarisation super junction structures: A simulation analysis

NASA Astrophysics Data System (ADS)

Unni, Vineet; Sankara Narayanan, E. M.

2017-04-01

This is the first report on the numerical analysis of the performance of nanoscale vertical superjunction structures based on impurity doping and an innovative approach that utilizes the polarisation properties inherent in III-V nitride semiconductors. Such nanoscale vertical polarisation super junction structures can be realized by employing a combination of epitaxial growth along the non-polar crystallographic axes of Wurtzite GaN and nanolithography-based processing techniques. Detailed numerical simulations clearly highlight the limitations of a doping based approach and the advantages of the proposed solution for breaking the unipolar one-dimensional material limits of GaN by orders of magnitude.

An ab initio study of the electronic structure of indium and gallium chalcogenide bilayers

NASA Astrophysics Data System (ADS)

Ayadi, T.; Debbichi, L.; Said, M.; Lebègue, S.

2017-09-01

Using first principle calculations, we have studied the structural and electronic properties of two dimensional bilayers of indium and gallium chalcogenides. With density functional theory corrected for van der Waals interactions, the different modes of stacking were investigated in a systematic way, and several of them were found to compete in energy. Then, their band structures were obtained with the GW approximation and found to correspond to indirect bandgap semiconductors with a small dependency on the mode of stacking. Finally, by analysing the electron density, it appeared that GaSe-InS is a promising system for electron-hole separation.

Electronic fitness function for screening semiconductors as thermoelectric materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, Guangzong; Sun, Jifeng; Li, Yuwei

Here, we introduce a simple but efficient electronic fitness function (EFF) that describes the electronic aspect of the thermoelectric performance. This EFF finds materials that overcome the inverse relationship between σ and S based on the complexity of the electronic structures regardless of specific origin (e.g., isosurface corrugation, valley degeneracy, heavy-light bands mixture, valley anisotropy or reduced dimensionality). This function is well suited for application in high throughput screening. We applied this function to 75 different thermoelectric and potential thermoelectric materials including full- and half-Heuslers, binary semiconductors, and Zintl phases. We find an efficient screening using this transport function. Themore » EFF identifies known high-performance p- and n-type Zintl phases and half-Heuslers. In addition, we find some previously unstudied phases with superior EFF.« less

Electronic fitness function for screening semiconductors as thermoelectric materials

DOE PAGES

Xing, Guangzong; Sun, Jifeng; Li, Yuwei; ...

2017-11-17

Here, we introduce a simple but efficient electronic fitness function (EFF) that describes the electronic aspect of the thermoelectric performance. This EFF finds materials that overcome the inverse relationship between σ and S based on the complexity of the electronic structures regardless of specific origin (e.g., isosurface corrugation, valley degeneracy, heavy-light bands mixture, valley anisotropy or reduced dimensionality). This function is well suited for application in high throughput screening. We applied this function to 75 different thermoelectric and potential thermoelectric materials including full- and half-Heuslers, binary semiconductors, and Zintl phases. We find an efficient screening using this transport function. Themore » EFF identifies known high-performance p- and n-type Zintl phases and half-Heuslers. In addition, we find some previously unstudied phases with superior EFF.« less

Atomic-Resolution Spectrum Imaging of Semiconductor Nanowires.

PubMed

Zamani, Reza R; Hage, Fredrik S; Lehmann, Sebastian; Ramasse, Quentin M; Dick, Kimberly A

2018-03-14

Over the past decade, III-V heterostructure nanowires have attracted a surge of attention for their application in novel semiconductor devices such as tunneling field-effect transistors (TFETs). The functionality of such devices critically depends on the specific atomic arrangement at the semiconductor heterointerfaces. However, most of the currently available characterization techniques lack sufficient spatial resolution to provide local information on the atomic structure and composition of these interfaces. Atomic-resolution spectrum imaging by means of electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) is a powerful technique with the potential to resolve structure and chemical composition with sub-angstrom spatial resolution and to provide localized information about the physical properties of the material at the atomic scale. Here, we demonstrate the use of atomic-resolution EELS to understand the interface atomic arrangement in three-dimensional heterostructures in semiconductor nanowires. We observed that the radial interfaces of GaSb-InAs heterostructure nanowires are atomically abrupt, while the axial interface in contrast consists of an interfacial region where intermixing of the two compounds occurs over an extended spatial region. The local atomic configuration affects the band alignment at the interface and, hence, the charge transport properties of devices such as GaSb-InAs nanowire TFETs. STEM-EELS thus represents a very promising technique for understanding nanowire physical properties, such as differing electrical behavior across the radial and axial heterointerfaces of GaSb-InAs nanowires for TFET applications.

High thermoelectric power factor in two-dimensional crystals of Mo S2

NASA Astrophysics Data System (ADS)

Hippalgaonkar, Kedar; Wang, Ying; Ye, Yu; Qiu, Diana Y.; Zhu, Hanyu; Wang, Yuan; Moore, Joel; Louie, Steven G.; Zhang, Xiang

2017-03-01

The quest for high-efficiency heat-to-electricity conversion has been one of the major driving forces toward renewable energy production for the future. Efficient thermoelectric devices require high voltage generation from a temperature gradient and a large electrical conductivity while maintaining a low thermal conductivity. For a given thermal conductivity and temperature, the thermoelectric power factor is determined by the electronic structure of the material. Low dimensionality (1D and 2D) opens new routes to a high power factor due to the unique density of states (DOS) of confined electrons and holes. The 2D transition metal dichalcogenide (TMDC) semiconductors represent a new class of thermoelectric materials not only due to such confinement effects but especially due to their large effective masses and valley degeneracies. Here, we report a power factor of Mo S2 as large as 8.5 mW m-1K-2 at room temperature, which is among the highest measured in traditional, gapped thermoelectric materials. To obtain these high power factors, we perform thermoelectric measurements on few-layer Mo S2 in the metallic regime, which allows us to access the 2D DOS near the conduction band edge and exploit the effect of 2D confinement on electron scattering rates, resulting in a large Seebeck coefficient. The demonstrated high, electronically modulated power factor in 2D TMDCs holds promise for efficient thermoelectric energy conversion.

Optical printed circuit board (O-PCB) and VLSI photonic integrated circuits: visions, challenges, and progresses

NASA Astrophysics Data System (ADS)

Lee, El-Hang; Lee, S. G.; O, B. H.; Park, S. G.; Noh, H. S.; Kim, K. H.; Song, S. H.

2006-09-01

A collective overview and review is presented on the original work conducted on the theory, design, fabrication, and in-tegration of micro/nano-scale optical wires and photonic devices for applications in a newly-conceived photonic systems called "optical printed circuit board" (O-PCBs) and "VLSI photonic integrated circuits" (VLSI-PIC). These are aimed for compact, high-speed, multi-functional, intelligent, light-weight, low-energy and environmentally friendly, low-cost, and high-volume applications to complement or surpass the capabilities of electrical PCBs (E-PCBs) and/or VLSI electronic integrated circuit (VLSI-IC) systems. These consist of 2-dimensional or 3-dimensional planar arrays of micro/nano-optical wires and circuits to perform the functions of all-optical sensing, storing, transporting, processing, switching, routing and distributing optical signals on flat modular boards or substrates. The integrated optical devices include micro/nano-scale waveguides, lasers, detectors, switches, sensors, directional couplers, multi-mode interference devices, ring-resonators, photonic crystal devices, plasmonic devices, and quantum devices, made of polymer, silicon and other semiconductor materials. For VLSI photonic integration, photonic crystals and plasmonic structures have been used. Scientific and technological issues concerning the processes of miniaturization, interconnection and integration of these systems as applicable to board-to-board, chip-to-chip, and intra-chip integration, are discussed along with applications for future computers, telecommunications, and sensor-systems. Visions and challenges toward these goals are also discussed.

Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd₃As₂.

PubMed

Jeon, Sangjun; Zhou, Brian B; Gyenis, Andras; Feldman, Benjamin E; Kimchi, Itamar; Potter, Andrew C; Gibson, Quinn D; Cava, Robert J; Vishwanath, Ashvin; Yazdani, Ali

2014-09-01

Condensed-matter systems provide a rich setting to realize Dirac and Majorana fermionic excitations as well as the possibility to manipulate them for potential applications. It has recently been proposed that chiral, massless particles known as Weyl fermions can emerge in certain bulk materials or in topological insulator multilayers and give rise to unusual transport properties, such as charge pumping driven by a chiral anomaly. A pair of Weyl fermions protected by crystalline symmetry effectively forming a massless Dirac fermion has been predicted to appear as low-energy excitations in a number of materials termed three-dimensional Dirac semimetals. Here we report scanning tunnelling microscopy measurements at sub-kelvin temperatures and high magnetic fields on the II-V semiconductor Cd3As2. We probe this system down to atomic length scales, and show that defects mostly influence the valence band, consistent with the observation of ultrahigh-mobility carriers in the conduction band. By combining Landau level spectroscopy and quasiparticle interference, we distinguish a large spin-splitting of the conduction band in a magnetic field and its extended Dirac-like dispersion above the expected regime. A model band structure consistent with our experimental findings suggests that for a magnetic field applied along the axis of the Dirac points, Weyl fermions are the low-energy excitations in Cd3As2.

Electronic structure properties of deep defects in hBN

NASA Astrophysics Data System (ADS)

Dev, Pratibha; Prdm Collaboration

In recent years, the search for room-temperature solid-state qubit (quantum bit) candidates has revived interest in the study of deep-defect centers in semiconductors. The charged NV-center in diamond is the best known amongst these defects. However, as a host material, diamond poses several challenges and so, increasingly, there is an interest in exploring deep defects in alternative semiconductors such as hBN. The layered structure of hBN makes it a scalable platform for quantum applications, as there is a greater potential for controlling the location of the deep defect in the 2D-matrix through careful experiments. Using density functional theory-based methods, we have studied the electronic and structural properties of several deep defects in hBN. Native defects within hBN layers are shown to have high spin ground states that should survive even at room temperature, making them interesting solid-state qubit candidates in a 2D matrix. Partnership for Reduced Dimensional Material (PRDM) is part of the NSF sponsored Partnerships for Research and Education in Materials (PREM).

Intracavity double diode structures with GaInP barrier layers for thermophotonic cooling

NASA Astrophysics Data System (ADS)

Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Hakkarainen, Teemu; Kivisaari, Pyry; Lyytikäinen, Jari; Aho, Arto; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani

2017-02-01

Optical cooling of semiconductors has recently been demonstrated both for optically pumped CdS nanobelts and for electrically injected GaInAsSb LEDs at very low powers. To enable cooling at larger power and to understand and overcome the main obstacles in optical cooling of conventional semiconductor structures, we study thermophotonic (TPX) heat transport in cavity coupled light emitters. Our structures consist of a double heterojunction (DHJ) LED with a GaAs active layer and a corresponding DHJ or a p-n-homojunction photodiode, enclosed within a single semiconductor cavity to eliminate the light extraction challenges. Our presently studied double diode structures (DDS) use GaInP barriers around the GaAs active layer instead of the AlGaAs barriers used in our previous structures. We characterize our updated double diode structures by four point probe IV- measurements and measure how the material modifications affect the recombination parameters and coupling quantum efficiencies in the structures. The coupling quantum efficiency of the new devices with InGaP barrier layers is found to be approximately 10 % larger than for the structures with AlGaAs barriers at the point of maximum efficiency.

Hybrid WSe2-In2O3 Phototransistor with Ultrahigh Detectivity by Efficient Suppression of Dark Currents.

PubMed

Guo, Nan; Gong, Fan; Liu, Junku; Jia, Yi; Zhao, Shaofan; Liao, Lei; Su, Meng; Fan, Zhiyong; Chen, Xiaoshuang; Lu, Wei; Xiao, Lin; Hu, Weida

2017-10-04

Photodetectors based on low-dimensional materials have attracted tremendous attention because of their high sensitivity and compatibility with conventional semiconductor technology. However, up until now, developing low-dimensional phototransistors with high responsivity and low dark currents over broad-band spectra still remains a great challenge because of the trade-offs in the potential architectures. In this work, we report a hybrid phototransistor consisting of a single In 2 O 3 nanowire as the channel material and a multilayer WSe 2 nanosheet as the decorating sensitizer for photodetection. Our devices show high responsivities of 7.5 × 10 5 and 3.5 × 10 4 A W -1 and ultrahigh detectivities of 4.17 × 10 17 and 1.95 × 10 16 jones at the wavelengths of 637 and 940 nm, respectively. The superior detectivity of the hybrid architecture arises from the extremely low dark currents and the enhanced photogating effect in the depletion regime by the unique design of energy band alignment of the channel and sensitizer materials. Moreover, the visible to near-infrared absorption properties of the multilayer WSe 2 nanosheet favor a broad-band spectral response for the devices. Our results pave the way for developing ultrahigh-sensitivity photodetectors based on low-dimensional hybrid architectures.

Structure and properties of microporous titanosilicate determined by first-principles calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, W.Y.; Xu, Y.; Gu, Z.

1996-12-01

The structure of EST-10, a member of synthetic microporous titanosilicates, was recently determined by an ingenious combination of experimental and simulational techniques. However, the locations of the alkali atoms in the framework remain elusive and its electronic structure is totally unknown. Based on first-principles local density calculations, the possible locations of the alkali atoms are identified and its electronic structure and bonding fully elucidated. ETS-10 is a semiconductor with a direct band gap of 2.33 eV. The Na atoms are likely to locate inside the seven-member ring pore adjacent to the one-dimensional Ti-O-Ti-O- chain. {copyright} {ital 1996 The American Physicalmore » Society.}« less

Noise and linearity optimization methods for a 1.9GHz low noise amplifier.

PubMed

Guo, Wei; Huang, Da-Quan

2003-01-01

Noise and linearity performances are critical characteristics for radio frequency integrated circuits (RFICs), especially for low noise amplifiers (LNAs). In this paper, a detailed analysis of noise and linearity for the cascode architecture, a widely used circuit structure in LNA designs, is presented. The noise and the linearity improvement techniques for cascode structures are also developed and have been proven by computer simulating experiments. Theoretical analysis and simulation results showed that, for cascode structure LNAs, the first metallic oxide semiconductor field effect transistor (MOSFET) dominates the noise performance of the LNA, while the second MOSFET contributes more to the linearity. A conclusion is thus obtained that the first and second MOSFET of the LNA can be designed to optimize the noise performance and the linearity performance separately, without trade-offs. The 1.9GHz Complementary Metal-Oxide-Semiconductor (CMOS) LNA simulation results are also given as an application of the developed theory.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahal, Rajendra P.; Bhat, Ishwara B.; Chow, Tat-Sing

Methods for facilitating fabricating semiconductor structures are provided which include: providing a multilayer structure including a semiconductor layer, the semiconductor layer including a dopant and having an increased conductivity; selectively increasing, using electrochemical processing, porosity of the semiconductor layer, at least in part, the selectively increasing porosity utilizing the increased conductivity of the semiconductor layer; and removing, at least in part, the semiconductor layer with the selectively increased porosity from the multilayer structure. By way of example, the selectively increasing porosity may include selectively, anodically oxidizing, at least in part, the semiconductor layer of the multilayer structure.

Periodic multilayer magnetized cold plasma containing a doped semiconductor

NASA Astrophysics Data System (ADS)

Nayak, Chittaranjan; Saha, Ardhendu; Aghajamali, Alireza

2018-07-01

The present work is to numerically investigate the properties of the defect mode in a one-dimensional photonic crystal made of magnetized cold plasma, doped by semiconductor. The defect mode of such kind of multilayer structure is analyzed by applying the character matrix method to each individual layer. Numerical results illustrate that the defect mode frequency can be tuned by varying the external magnetic field, the electron density, and the thickness of the defect layer. Moreover, the behavior of the defect mode was found to be quite interesting when study the oblique incidence. It was found that for both right- and left-hand polarized transversal magnetic waves, the defect mode of the proposed defective structure disappears when the angle of incidence is larger than a particular oblique incidence. For the left-hand polarized transversal electric wave, however, an additional defect mode was noticed. The results lead to some new information concerning the designing of new types of tunable narrowband microwave filters.

Periodic multilayer magnetized cold plasma containing a doped semiconductor

NASA Astrophysics Data System (ADS)

Nayak, Chittaranjan; Saha, Ardhendu; Aghajamali, Alireza

2018-02-01

The present work is to numerically investigate the properties of the defect mode in a one-dimensional photonic crystal made of magnetized cold plasma, doped by semiconductor. The defect mode of such kind of multilayer structure is analyzed by applying the character matrix method to each individual layer. Numerical results illustrate that the defect mode frequency can be tuned by varying the external magnetic field, the electron density, and the thickness of the defect layer. Moreover, the behavior of the defect mode was found to be quite interesting when study the oblique incidence. It was found that for both right- and left-hand polarized transversal magnetic waves, the defect mode of the proposed defective structure disappears when the angle of incidence is larger than a particular oblique incidence. For the left-hand polarized transversal electric wave, however, an additional defect mode was noticed. The results lead to some new information concerning the designing of new types of tunable narrowband microwave filters.

Highly Enhanced Many-Body Interactions in Anisotropic 2D Semiconductors.

PubMed

Sharma, Ankur; Yan, Han; Zhang, Linglong; Sun, Xueqian; Liu, Boqing; Lu, Yuerui

2018-05-15

Atomically thin two-dimensional (2D) semiconductors have presented a plethora of opportunities for future optoelectronic devices and photonics applications, made possible by the strong light matter interactions at the 2D quantum limit. Many body interactions between fundamental particles in 2D semiconductors are strongly enhanced compared with those in bulk semiconductors because of the reduced dimensionality and, thus, reduced dielectric screening. These enhanced many body interactions lead to the formation of robust quasi-particles, such as excitons, trions, and biexcitons, which are extremely important for the optoelectronics device applications of 2D semiconductors, such as light emitting diodes, lasers, and optical modulators, etc. Recently, the emerging anisotropic 2D semiconductors, such as black phosphorus (termed as phosphorene) and phosphorene-like 2D materials, such as ReSe 2 , 2D-perovskites, SnS, etc., show strong anisotropic optical and electrical properties, which are different from conventional isotropic 2D semiconductors, such as transition metal dichalcogenide (TMD) monolayers. This anisotropy leads to the formation of quasi-one-dimensional (quasi-1D) excitons and trions in a 2D system, which results in even stronger many body interactions in anisotropic 2D materials, arising from the further reduced dimensionality of the quasi-particles and thus reduced dielectric screening. Many body interactions have been heavily investigated in TMD monolayers in past years, but not in anisotropic 2D materials yet. The quasi-particles in anisotropic 2D materials have fractional dimensionality which makes them perfect candidates to serve as a platform to study fundamental particle interactions in fractional dimensional space. In this Account, we present our recent progress related to 2D phosphorene, a 2D system with quasi-1D excitons and trions. Phosphorene, because of its unique anisotropic properties, provides a unique 2D platform for investigating the dynamics of excitons, trions, and biexcitons in reduced dimensions and fundamental many body interactions. We begin by explaining the fundamental reasons for the highly enhanced interactions in the 2D systems influenced by dielectric screening, resulting in high binding energies of excitons and trions, which are supported by theoretical calculations and experimental observations. Phosphorene has shown much higher binding energies of excitons and trions than TMD monolayers, which allows robust quasi-particles in anisotropic materials at room temperature. We also discuss the role of extrinsic defects induced in phosphorene, resulting in localized excitonic emissions in the near-infrared range, making it suitable for optical telecommunication applications. Finally, we present our vision of the exciting device applications based on the highly enhanced many body interactions in phosphorene, including exciton-polariton devices, polariton lasers, single-photon emitters, and tunable light emitting diodes (LEDs).

Preface: phys. stat. sol. (c) 1/8

NASA Astrophysics Data System (ADS)

Amann, Markus C.

2004-07-01

In this special issue of physica status solidi (c) we have included 10 invited papers reviewing the current state-of-the-art and the progress achieved in materials science, semiconductor theory, novel physical mechanisms and advanced device concepts in the field of nanostructured electronic and optoelectronic semiconductor devices. All of these papers were written by previous members of the Collaborative Research Centre 348 Nanometer-Halbleiterbauelemente: Grundlagen - Konzepte - Realisierungen (Nanometer Semiconductor Devices: Fundamentals - Concepts - Realisations), which was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) during the period from 1991 to 2003. In these twelve years, the researchers in this programme have carried an intense activity directed towards two main objectives. First of all, Fundamentals and Concepts of nanostructure devices and their technology were explored theoretically and experimentally including the effects of low-dimensional structures on carrier transport, optical properties and spin, as well as the enabling epitaxial and nanostructure technologies such as the cleaved-edge-overgrowth technique and the self-assembled growth of quantum dots. A second field of interest was focused towards the design and development of Novel Semiconductor Devices exploiting nanostructure technology. This comprises optical detectors and memories with nanometer lateral dimensions, microwave detectors and sources up to the 300 GHz regime, innovative tunable and surface-emitting semiconductor lasers for the wavelength range 0.9 to 2 m, and nitride-based resonant tunnelling diodes. Some of the device innovations have meanwhile become commercial products proving also the practical importance of this research area. The articles in this special issue relate to the projects of the last three-years' funding period from 2000 to 2003 and are organized along these two We would like to thank the numerous reviewers for their valuable comments and the editorial staff of physica status solidi (c) for their extremely helpful support. The funding by the German Research Foundation over the full project time and the continued monitoring and advice by its representatives Dr. Klaus Wehrberger and Dr. Peter Heil are gratefully acknowledged by all previous members and co-workers of this Collaborative Research Centre.

Ferroelectricity in Covalently functionalized Two-dimensional Materials: Integration of High-mobility Semiconductors and Nonvolatile Memory.

PubMed

Wu, Menghao; Dong, Shuai; Yao, Kailun; Liu, Junming; Zeng, Xiao Cheng

2016-11-09

Realization of ferroelectric semiconductors by conjoining ferroelectricity with semiconductors remains a challenging task because most present-day ferroelectric materials are unsuitable for such a combination due to their wide bandgaps. Herein, we show first-principles evidence toward the realization of a new class of two-dimensional (2D) ferroelectric semiconductors through covalent functionalization of many prevailing 2D materials. Members in this new class of 2D ferroelectric semiconductors include covalently functionalized germanene, and stanene (Nat. Commun. 2014, 5, 3389), as well as MoS 2 monolayer (Nat. Chem. 2015, 7, 45), covalent functionalization of the surface of bulk semiconductors such as silicon (111) (J. Phys. Chem. B 2006, 110 , 23898), and the substrates of oxides such as silica with self-assembly monolayers (Nano Lett. 2014, 14, 1354). The newly predicted 2D ferroelectric semiconductors possess high mobility, modest bandgaps, and distinct ferroelectricity that can be exploited for developing various heterostructural devices with desired functionalities. For example, we propose applications of the 2D materials as 2D ferroelectric field-effect transistors with ultrahigh on/off ratio, topological transistors with Dirac Fermions switchable between holes and electrons, ferroelectric junctions with ultrahigh electro-resistance, and multiferroic junctions for controlling spin by electric fields. All these heterostructural devices take advantage of the combination of high-mobility semiconductors with fast writing and nondestructive reading capability of nonvolatile memory, thereby holding great potential for the development of future multifunctional devices.

Stability and electronic properties of low-dimensional nanostructures

NASA Astrophysics Data System (ADS)

Guan, Jie

As the devices used in daily life become smaller and more concentrated, traditional three-dimensional (3D) bulk materials have reached their limit in size. Low-dimensional nanomaterials have been attracting more attention in research and getting widely applied in many industrial fields because of their atomic-level size, unique advanced properties, and varied nanostructures. In this thesis, I have studied the stability and mechanical and electronic properties of zero-dimensional (0D) structures including carbon fullerenes, nanotori, metallofullerenes and phosphorus fullerenes, one-dimensional (1D) structures including carbon nanotubes and phosphorus nanotubes, as well as two-dimensional (2D) structures including layered transition metal dichalcogenides (TMDs), phosphorene and phosphorus carbide (PC). I first briefly introduce the scientific background and the motivation of all the work in this thesis. Then the computational techniques, mainly density functional theory (DFT), are reviewed in Chapter 2. In Chapter 3, I investigate the stability and electronic structure of endohedral rare-earth metallofullerene La C60 and the trifluoromethylized La C60(CF3)n with n ≤ 5. Odd n is preferred due to the closed-shell electronic configuration or large HOMO-LUMO gap, which is also meaningful for the separation of C 60-based metallofullerenes. Mechanical and electronic properties of layered materials including TMDs and black phosphorus are studied in Chapter 4 and 5. In Chapter 4, a metallic NbSe2/semiconducting WSe2 bilayer is investigated and besides a rigid band shift associated with charge transfer, the presence of NbSe2 does not modify the electronic structure of WSe2. Structural similarity and small lattice mismatch results in the heterojunction being capable of efficiently transferring charge acrossthe interface. In Chapter 5, I investigate the dependence of stability and electronic band structure on the in-layer strain in bulk black phosphorus. In Chapters 6, 7 and 8, novel 2D structures are predicted theoretically. In Chapter 6, I propose two new stable structural phases of layered phosphorus besides the layered alpha-P (black) and beta-P (blue) phosphorus allotropes. A metal-insulator transition caused by inlayer strain or changing the number of layers is found in the new gamma-P phase. An unforeseen benefit is the possibility to connect different structural phases at no energy cost, which further leads to a paradigm of constructing very stable, faceted phosphorus nanotube and fullerene structures by laterally joining nanoribbons or patches of different planar phosphorene phases, which is discussed in Chapter 7. In Chapter 8, I propose previously unknown allotropes of PC in the stable shape of an atomically thin layer. Different stable geometries, which result from the competition between sp2 bonding found in graphitic C and sp3 bonding found in black P, display different electronic properties including metallic, semi-metallic with an anisotropic Dirac cone, and direct-gap semiconductors with their gap tunable by in-layer strain. In Chapter 9, I propose a fast method to determine the local curvature in 2D systems with arbitrary shape. The curvature information, combined with elastic constants obtained for a planar system, provides an accurate estimate of the local stability in the framework of continuum elasticity theory. This approach can be applied to all 2D structures. Finally, I present general conclusions from the PhD Thesis work in Chapter 10.

Surface morphology and electrical properties of Au/Ni/ Left-Pointing-Angle-Bracket C Right-Pointing-Angle-Bracket /n-Ga{sub 2}O{sub 3}/p-GaSe Left-Pointing-Angle-Bracket KNO{sub 3} Right-Pointing-Angle-Bracket hybrid structures fabricated on the basis of a layered semiconductor with nanoscale ferroelectric inclusions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakhtinov, A. P., E-mail: chimsp@ukrpost.ua; Vodopyanov, V. N.; Netyaga, V. V.

2012-03-15

Features of the formation of Au/Ni/ Left-Pointing-Angle-Bracket C Right-Pointing-Angle-Bracket /n-Ga{sub 2}O{sub 3} hybrid nanostructures on a Van der Waals surface (0001) of 'layered semiconductor-ferroelectric' composite nanostructures (p-GaSe Left-Pointing-Angle-Bracket KNO{sub 3} Right-Pointing-Angle-Bracket ) are studied using atomic-force microscopy. The room-temperature current-voltage characteristics and the dependence of the impedance spectrum of hybrid structures on a bias voltage are studied. The current-voltage characteristic includes a resonance peak and a portion with negative differential resistance. The current attains a maximum at a certain bias voltage, when electric polarization switching in nanoscale three-dimensional inclusions in the layered GaSe matrix occurs. In the high-frequency region (fmore » > 10{sup 6} Hz), inductive-type impedance (a large negative capacitance of structures, {approx}10{sup 6} F/mm{sup 2}) is detected. This effect is due to spinpolarized electron transport in a series of interconnected semiconductor composite nanostructures with multiple p-GaSe Left-Pointing-Angle-Bracket KNO{sub 3} Right-Pointing-Angle-Bracket quantum wells and a forward-biased 'ferromagnetic metal-semiconductor' polarizer (Au/Ni/ Left-Pointing-Angle-Bracket C Right-Pointing-Angle-Bracket /n{sup +}-Ga{sub 2}O{sub 3}/n-Ga{sub 2}O{sub 3}). A shift of the maximum (current hysteresis) is detected in the current-voltage characteristics for various directions of the variations in bias voltage.« less

Monolithically integrated two-dimensional arrays of optoelectronic threshold devices for neural network applications

NASA Technical Reports Server (NTRS)

Kim, J. H.; Katz, J.; Lin, S. H.; Psaltis, D.

1989-01-01

A monolithic 10 x 10 two-dimensional array of 'optical neuron' optoelectronic threshold elements for neural network applications has been designed, fabricated, and tested. Overall array dimensions are 5 x 5 mm, while the individual neurons, composed of an LED that is driven by a double-heterojunction bipolar transistor, are 250 x 250 microns. The overall integrated structure exhibited semiconductor-controlled rectifier characteristics, with a breakover voltage of 75 V and a reverse-breakdown voltage of 60 V; this is attributable to the parasitic p-n-p transistor which exists as a result of the sharing of the same n-AlGaAs collector between the transistors and the LED.

Electron energy loss spectroscopy on semiconductor heterostructures for optoelectronics and photonics applications.

PubMed

Eljarrat, A; López-Conesa, L; Estradé, S; Peiró, F

2016-05-01

In this work, we present characterization methods for the analysis of nanometer-sized devices, based on silicon and III-V nitride semiconductor materials. These methods are devised in order to take advantage of the aberration corrected scanning transmission electron microscope, equipped with a monochromator. This set-up ensures the necessary high spatial and energy resolution for the characterization of the smallest structures. As with these experiments, we aim to obtain chemical and structural information, we use electron energy loss spectroscopy (EELS). The low-loss region of EELS is exploited, which features fundamental electronic properties of semiconductor materials and facilitates a high data throughput. We show how the detailed analysis of these spectra, using theoretical models and computational tools, can enhance the analytical power of EELS. In this sense, initially, results from the model-based fit of the plasmon peak are presented. Moreover, the application of multivariate analysis algorithms to low-loss EELS is explored. Finally, some physical limitations of the technique, such as spatial delocalization, are mentioned. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Nanowire Optoelectronics

NASA Astrophysics Data System (ADS)

Wang, Zhihuan; Nabet, Bahram

2015-12-01

Semiconductor nanowires have been used in a variety of passive and active optoelectronic devices including waveguides, photodetectors, solar cells, light-emitting diodes (LEDs), lasers, sensors, and optical antennas. We review the optical properties of these nanowires in terms of absorption, guiding, and radiation of light, which may be termed light management. Analysis of the interaction of light with long cylindrical/hexagonal structures with subwavelength diameters identifies radial resonant modes, such as Leaky Mode Resonances, or Whispering Gallery modes. The two-dimensional treatment should incorporate axial variations in "volumetric modes,"which have so far been presented in terms of Fabry-Perot (FP), and helical resonance modes. We report on finite-difference timedomain (FDTD) simulations with the aim of identifying the dependence of these modes on geometry (length, width), tapering, shape (cylindrical, hexagonal), core-shell versus core-only, and dielectric cores with semiconductor shells. This demonstrates how nanowires (NWs) form excellent optical cavities without the need for top and bottommirrors. However, optically equivalent structures such as hexagonal and cylindrical wires can have very different optoelectronic properties meaning that light management alone does not sufficiently describe the observed enhancement in upward (absorption) and downward transitions (emission) of light inNWs; rather, the electronic transition rates should be considered. We discuss this "rate management" scheme showing its strong dimensional dependence, making a case for photonic integrated circuits (PICs) that can take advantage of the confluence of the desirable optical and electronic properties of these nanostructures.

Physics of Quantum Structures in Photovoltaic Devices

NASA Technical Reports Server (NTRS)

Raffaelle, Ryne P.; Andersen, John D.

2005-01-01

There has been considerable activity recently regarding the possibilities of using various nanostructures and nanomaterials to improve photovoltaic conversion of solar energy. Recent theoretical results indicate that dramatic improvements in device efficiency may be attainable through the use of three-dimensional arrays of zero-dimensional conductors (i.e., quantum dots) in an ordinary p-i-n solar cell structure. Quantum dots and other nanostructured materials may also prove to have some benefits in terms of temperature coefficients and radiation degradation associated with space solar cells. Two-dimensional semiconductor superlattices have already demonstrated some advantages in this regard. It has also recently been demonstrated that semiconducting quantum dots can also be used to improve conversion efficiencies in polymeric thin film solar cells. Improvement in thin film cells utilizing conjugated polymers has also be achieved through the use of one-dimensional quantum structures such as carbon nanotubes. It is believed that carbon nanotubes may contribute to both the disassociation as well as the carrier transport in the conjugated polymers used in certain thin film photovoltaic cells. In this paper we will review the underlying physics governing some of the new photovoltaic nanostructures being pursued, as well as the the current methods being employed to produce III-V, II-VI, and even chalcopyrite-based nanomaterials and nanostructures for solar cells.

Measurement of the quantum capacitance from two-dimensional surface state of a topological insulator at room temperature

NASA Astrophysics Data System (ADS)

Choi, Hyunwoo; Kim, Tae Geun; Shin, Changhwan

2017-06-01

A topological insulator (TI) is a new kind of material that exhibits unique electronic properties owing to its topological surface state (TSS). Previous studies focused on the transport properties of the TSS, since it can be used as the active channel layer in metal-oxide-semiconductor field-effect transistors (MOSFETs). However, a TI with a negative quantum capacitance (QC) effect can be used in the gate stack of MOSFETs, thereby facilitating the creation of ultra-low power electronics. Therefore, it is important to study the physics behind the QC in TIs in the absence of any external magnetic field, at room temperature. We fabricated a simple capacitor structure using a TI (TI-capacitor: Au-TI-SiO2-Si), which shows clear evidence of QC at room temperature. In the capacitance-voltage (C-V) measurement, the total capacitance of the TI-capacitor increases in the accumulation regime, since QC is the dominant capacitive component in the series capacitor model (i.e., CT-1 = CQ-1 + CSiO2-1). Based on the QC model of the two-dimensional electron systems, we quantitatively calculated the QC, and observed that the simulated C-V curve theoretically supports the conclusion that the QC of the TI-capacitor is originated from electron-electron interaction in the two-dimensional surface state of the TI.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

PubMed Central

Vollebregt, Sten; Ishihara, Ryoichi

2015-01-01

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used. PMID:26709530

Study of the pulse characteristics of semiconductor lasers with a broadened waveguide at low temperatures (110–120 K)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veselov, D. A.; Shashkin, I. S.; Bobretsova, Yu. K.

2016-10-15

Pulse-pumped MOVPE-fabricated (metal-organic vapor-phase epitaxy) semiconductor lasers emitting in the spectral ranges 1000–1100 and 1400–1600 nm at temperatures of 110–120 K are studied. It is found that cooling the lasers for both spectral ranges to low temperature results in their light–current curves approaching linearity, and an optical power of, respectively, 110 and 20 W can be attained. The low-temperature effect is reduced for lasers emitting in the spectral range 1400–1600 nm. The processes affecting a rise in the internal optical loss in semiconductor lasers are considered. It is shown that an increase in the carrier concentration in the waveguide ofmore » a laser structure greatly depends on temperature and is determined by the noninstantaneous capture (capture rate) of carriers from the waveguide into the active region. It is demonstrated that, upon lowering the temperature to 115K, the concentration of electrons and holes in the waveguide becomes lower, which leads to a significant decrease in the internal optical loss and to an increase in the output optical power of the semiconductor laser.« less

Structured-gate organic field-effect transistors

NASA Astrophysics Data System (ADS)

Aljada, Muhsen; Pandey, Ajay K.; Velusamy, Marappan; Burn, Paul L.; Meredith, Paul; Namdas, Ebinazar B.

2012-06-01

We report the fabrication and electrical characteristics of structured-gate organic field-effect transistors consisting of a gate electrode patterned with three-dimensional pillars. The pillar gate electrode was over-coated with a gate dielectric (SiO2) and solution processed organic semiconductors producing both unipolar p-type and bipolar behaviour. We show that this new structured-gate architecture delivers higher source-drain currents, higher gate capacitance per unit equivalent linear channel area, and enhanced charge injection (electrons and/or holes) versus the conventional planar structure in all modes of operation. For the bipolar field-effect transistor (FET) the maximum source-drain current enhancements in p- and n-channel mode were >600% and 28%, respectively, leading to p and n charge mobilities with the same order of magnitude. Thus, we have demonstrated that it is possible to use the FET architecture to manipulate and match carrier mobilities of material combinations where one charge carrier is normally dominant. Mobility matching is advantageous for creating organic logic circuit elements such as inverters and amplifiers. Hence, the method represents a facile and generic strategy for improving the performance of standard organic semiconductors as well as new materials and blends.

A stable solution-processed polymer semiconductor with record high-mobility for printed transistors

PubMed Central

Li, Jun; Zhao, Yan; Tan, Huei Shuan; Guo, Yunlong; Di, Chong-An; Yu, Gui; Liu, Yunqi; Lin, Ming; Lim, Suo Hon; Zhou, Yuhua; Su, Haibin; Ong, Beng S.

2012-01-01

Microelectronic circuits/arrays produced via high-speed printing instead of traditional photolithographic processes offer an appealing approach to creating the long-sought after, low-cost, large-area flexible electronics. Foremost among critical enablers to propel this paradigm shift in manufacturing is a stable, solution-processable, high-performance semiconductor for printing functionally capable thin-film transistors — fundamental building blocks of microelectronics. We report herein the processing and optimisation of solution-processable polymer semiconductors for thin-film transistors, demonstrating very high field-effect mobility, high on/off ratio, and excellent shelf-life and operating stabilities under ambient conditions. Exceptionally high-gain inverters and functional ring oscillator devices on flexible substrates have been demonstrated. This optimised polymer semiconductor represents a significant progress in semiconductor development, dispelling prevalent skepticism surrounding practical usability of organic semiconductors for high-performance microelectronic devices, opening up application opportunities hitherto functionally or economically inaccessible with silicon technologies, and providing an excellent structural framework for fundamental studies of charge transport in organic systems. PMID:23082244

Strain-tuning of the optical properties of semiconductor nanomaterials by integration onto piezoelectric actuators

NASA Astrophysics Data System (ADS)

Martín-Sánchez, Javier; Trotta, Rinaldo; Mariscal, Antonio; Serna, Rosalía; Piredda, Giovanni; Stroj, Sandra; Edlinger, Johannes; Schimpf, Christian; Aberl, Johannes; Lettner, Thomas; Wildmann, Johannes; Huang, Huiying; Yuan, Xueyong; Ziss, Dorian; Stangl, Julian; Rastelli, Armando

2018-01-01

The tailoring of the physical properties of semiconductor nanomaterials by strain has been gaining increasing attention over the last years for a wide range of applications such as electronics, optoelectronics and photonics. The ability to introduce deliberate strain fields with controlled magnitude and in a reversible manner is essential for fundamental studies of novel materials and may lead to the realization of advanced multi-functional devices. A prominent approach consists in the integration of active nanomaterials, in thin epitaxial films or embedded within carrier nanomembranes, onto Pb(Mg1/3Nb2/3)O3-PbTiO3-based piezoelectric actuators, which convert electrical signals into mechanical deformation (strain). In this review, we mainly focus on recent advances in strain-tunable properties of self-assembled InAs quantum dots (QDs) embedded in semiconductor nanomembranes and photonic structures. Additionally, recent works on other nanomaterials like rare-earth and metal-ion doped thin films, graphene and MoS2 or WSe2 semiconductor two-dimensional materials are also reviewed. For the sake of completeness, a comprehensive comparison between different procedures employed throughout the literature to fabricate such hybrid piezoelectric-semiconductor devices is presented. It is shown that unprocessed piezoelectric substrates (monolithic actuators) allow to obtain a certain degree of control over the nanomaterials’ emission properties such as their emission energy, fine-structure-splitting in self-assembled InAs QDs and semiconductor 2D materials, upconversion phenomena in BaTiO3 thin films or piezotronic effects in ZnS:Mn films and InAs QDs. Very recently, a novel class of micro-machined piezoelectric actuators have been demonstrated for a full control of in-plane stress fields in nanomembranes, which enables producing energy-tunable sources of polarization-entangled photons in arbitrary QDs. Future research directions and prospects are discussed.

Three-terminal heterojunction bipolar transistor solar cell for high-efficiency photovoltaic conversion.

PubMed

Martí, A; Luque, A

2015-04-22

Here we propose, for the first time, a solar cell characterized by a semiconductor transistor structure (n/p/n or p/n/p) where the base-emitter junction is made of a high-bandgap semiconductor and the collector is made of a low-bandgap semiconductor. We calculate its detailed-balance efficiency limit and prove that it is the same one than that of a double-junction solar cell. The practical importance of this result relies on the simplicity of the structure that reduces the number of layers that are required to match the limiting efficiency of dual-junction solar cells without using tunnel junctions. The device naturally emerges as a three-terminal solar cell and can also be used as building block of multijunction solar cells with an increased number of junctions.

Three-terminal heterojunction bipolar transistor solar cell for high-efficiency photovoltaic conversion

PubMed Central

Martí, A.; Luque, A.

2015-01-01

Here we propose, for the first time, a solar cell characterized by a semiconductor transistor structure (n/p/n or p/n/p) where the base–emitter junction is made of a high-bandgap semiconductor and the collector is made of a low-bandgap semiconductor. We calculate its detailed-balance efficiency limit and prove that it is the same one than that of a double-junction solar cell. The practical importance of this result relies on the simplicity of the structure that reduces the number of layers that are required to match the limiting efficiency of dual-junction solar cells without using tunnel junctions. The device naturally emerges as a three-terminal solar cell and can also be used as building block of multijunction solar cells with an increased number of junctions. PMID:25902374

Analysis of quantum semiconductor heterostructures by ballistic electron emission spectroscopy

NASA Astrophysics Data System (ADS)

Guthrie, Daniel K.

1998-09-01

The microelectronics industry is diligently working to achieve the goal of gigascale integration (GSI) by early in the 21st century. For the past twenty-five years, progress toward this goal has been made by continually scaling down device technology. Unfortunately, this trend cannot continue to the point of producing arbitrarily small device sizes. One possible solution to this problem that is currently under intensive study is the relatively new area of quantum devices. Quantum devices represent a new class of microelectronic devices that operate by utilizing the wave-like nature (reflection, refraction, and confinement) of electrons together with the laws of quantum mechanics to construct useful devices. One difficulty associated with these structures is the absence of measurement techniques that can fully characterize carrier transport in such devices. This thesis addresses this need by focusing on the study of carrier transport in quantum semiconductor heterostructures using a relatively new and versatile measurement technique known as ballistic electron emission spectroscopy (BEES). To achieve this goal, a systematic approach that encompasses a set of progressively more complex structures is utilized. First, the simplest BEES structure possible, the metal/semiconductor interface, is thoroughly investigated in order to provide a foundation for measurements on more the complex structures. By modifying the semiclassical model commonly used to describe the experimental BEES spectrum, a very complete and accurate description of the basic structure has been achieved. Next, a very simple semiconductor heterostructure, a Ga1-xAlxAs single-barrier structure, was measured and analyzed. Low-temperature measurements on this structure were used to investigate the band structure and electron-wave interference effects in the Ga1-xAlxAs single barrier structure. These measurements are extended to a simple quantum device by designing, measuring, and analyzing a set of complementary electron-wave Fabry-Perot quantum interference filters which included both a half- and a quarter-electron-wavelength resonant device. High-resolution, low noise, BEES spectra obtained on these devices at low-temperature were used to measure the zero-bias electron transmittance as a function of injected energy for these resonant devices. Finally, by analyzing BEES spectra taken at various spatial locations, one monolayer variations in the thickness of a buried quantum well have been detected.

Synthesis and characterization of group IV semiconductor nanowires by vapor-liquid-solid growth

NASA Astrophysics Data System (ADS)

Lew, Kok-Keong

There is currently intense interest in one-dimensional nanostructures, such as nanotubes and nanowires, due to their potential to test fundamental concepts of dimensionality and to serve as building blocks for nanoscale devices. Vapor-liquid-solid (VLS) growth, which is one of the most common fabrication methods, has been used to produce single crystal semiconductor nanowires such as silicon (Si), germanium (Ge), and gallium arsenide (GaAs). In the VLS growth of Group IV semiconductor nanowires, a metal, such as gold (Au) is used as a catalyst agent to nucleate whisker growth from a Si-containing (silane (SIH4)) or Ge-containing vapor (germane (GeH 4)). Au and Si/Ge form a liquid alloy that has a eutectic temperature of around 360°C, which, upon supersaturation, nucleates the growth of a Si or Ge wire. The goal of this work is to develop a more fundamental understanding of VLS growth kinetics and intentional doping of Group IV semiconductor nanowires in order to better control the properties of the nanowires. The fabrication of p-type and n-type Si nanowires will be studied via the addition of dopant gases such as diborane (B2H 6), trimethylboron (TMB), and phosphine (PH3) during growth. The use of gaseous dopant sources provides more flexibility in growth, particularly for the fabrication of p-n junctions and structures with axial dopant variations (e.g. p+-p- p+). The study is then extended to fabricate SiGe alloy nanowires by mixing SiH4 and GeH4. Bandgap engineering in Si/SiGe heterostructures can lead to novel devices with improved performance compared to those made entirely of Si. The scientific findings will lead to a better understanding of the fabrication of Si/SiGe axial and radial heterostructure nanowires for functional nanowire device structures, such as heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs). Eventually, the central theme of this research is to provide a scientific knowledge base and foundation for the design of Si, Ge, and SiGe nanostructures that will be of importance in nanoscale device applications.

Direct solar pumping of semiconductor lasers: A feasibility study

NASA Technical Reports Server (NTRS)

Anderson, Neal G.

1992-01-01

This report describes results of NASA Grant NAG-1-1148, entitled Direct Solar Pumping of Semiconductor Lasers: A Feasibility Study. The goals of this study were to provide a preliminary assessment of the feasibility of pumping semiconductor lasers in space with directly focused sunlight and to identify semiconductor laser structures expected to operate at the lowest possible focusing intensities. It should be emphasized that the structures under consideration would provide direct optical-to-optical conversion of sunlight into laser light in a single crystal, in contrast to a configuration consisting of a solar cell or storage battery electrically pumping a current injection laser. With external modulation, such lasers could perhaps be efficient sources for intersatellite communications. We proposed specifically to develop a theoretical model of semiconductor quantum-well lasers photopumped by a broadband source, test it against existing experimental data where possible, and apply it to estimating solar pumping requirements and identifying optimum structures for operation at low pump intensities. These tasks have been accomplished, as described in this report of our completed project. The report is organized as follows: Some general considerations relevant to the solar-pumped semiconductor laser problem are discussed in Section 2, and the types of structures chosen for specific investigation are described. The details of the laser model we developed for this work are then outlined in Section 3. In Section 4, results of our study are presented, including designs for optimum lattice-matched and strained-layer solar-pumped quantum-well lasers and threshold pumping estimates for these structures. It was hoped at the outset of this work that structures could be identified which could be expected to operate continuously at solar photoexcitation intensities of several thousand suns, and this indeed turned out to be the case as described in this section. Our project is summarized in Section 5, and information on publications resulting from this work is provided in Section 6.

Microscopic structure and electrical transport property of sputter-deposited amorphous indium-gallium-zinc oxide semiconductor films

NASA Astrophysics Data System (ADS)

Yabuta, H.; Kaji, N.; Shimada, M.; Aiba, T.; Takada, K.; Omura, H.; Mukaide, T.; Hirosawa, I.; Koganezawa, T.; Kumomi, H.

2014-06-01

We report on microscopic structures and electrical and optical properties of sputter-deposited amorphous indium-gallium-zinc oxide (a-IGZO) films. From electron microscopy observations and an x-ray small angle scattering analysis, it has been confirmed that the sputtered a-IGZO films consist of a columnar structure. However, krypton gas adsorption measurement revealed that boundaries of the columnar grains are not open-pores. The conductivity of the sputter-deposited a-IGZO films shows a change as large as seven orders of magnitude depending on post-annealing atmosphere; it is increased by N2-annealing and decreased by O2-annealing reversibly, at a temperature as low as 300°C. This large variation in conductivity is attributed to thermionic emission of carrier electrons through potential barriers at the grain boundaries, because temperature dependences of the carrier density and the Hall mobility exhibit thermal activation behaviours. The optical band-gap energy of the a-IGZO films changes between before and after annealing, but is independent of the annealing atmosphere, in contrast to the noticeable dependence of conductivity described above. For exploring other possibilities of a-IGZO, we formed multilayer films with an artificial periodic lattice structure consisting of amorphous InO, GaO, and ZnO layers, as an imitation of the layer-structured InGaZnO4 homologous phase. The hall mobility of the multilayer films was almost constant for thicknesses of the constituent layer between 1 and 6 Å, suggesting rather small contribution of lateral two-dimensional conduction It increased with increasing the thickness in the range from 6 to 15 Å, perhaps owing to an enhancement of two-dimensional conduction in InO layers.

III-V/II-VI Hybrid Quantum Well Mid-Infrared Lasers

DTIC Science & Technology

2005-01-25

semiconductor lasers are of great importance for many applications such as laser diode spectroscopy , pollution monitoring, low-loss optical communication...great importance for many applications such as laser diode spectroscopy, pollutant monitoring, low-losses longwavelength optical communication...InAsSb/CdMgSe laser structure 1.2. Characterization of the laser structures and interface quality (STM, EPFM etc) 1.3. Study of spontaneous and

N-Functionalized MXenes: ultrahigh carrier mobility and multifunctional properties.

PubMed

Shao, Yangfan; Zhang, Fang; Shi, Xingqiang; Pan, Hui

2017-11-01

Two dimensional (2D) nanomaterials have demonstrated huge potential in wide applications from nanodevices to energy harvesting/storage. In this work, we propose a new class of 2D monolayers, nitrogen-functionalized MXenes (Nb 2 CN 2 and Ta 2 CN 2 ), based on density-functional theory (DFT). We find that these monolayers are direct semiconductors with near linear energy dispersions at the Γ point. M 2 CN 2 monolayers have significant small effective mass and show an ultra-high mobility of up to 10 6 cm 2 V -1 s -1 . We show that the electronic structures of the M 2 CN 2 monolayers can be easily controlled by biaxial and uniaxial strains. Importantly, the carrier mobility and direct band gap can be dramatically increased within a certain range of strain. A direct-indirect band gap transition can be triggered and the band gap can be tuned under strain. The tunable electronic properties are attributed to the structural changes and charge redistribution under stain. Our findings demonstrate that N-functionalized MXenes are promising materials for nanodevices with high speed and low power.

Single-mode tunable laser emission in the single-exciton regime from colloidal nanocrystals

PubMed Central

Grivas, Christos; Li, Chunyong; Andreakou, Peristera; Wang, Pengfei; Ding, Ming; Brambilla, Gilberto; Manna, Liberato; Lagoudakis, Pavlos

2013-01-01

Whispering-gallery-mode resonators have been extensively used in conjunction with different materials for the development of a variety of photonic devices. Among the latter, hybrid structures, consisting of dielectric microspheres and colloidal core/shell semiconductor nanocrystals as gain media, have attracted interest for the development of microlasers and studies of cavity quantum electrodynamic effects. Here we demonstrate single-exciton, single-mode, spectrally tuned lasing from ensembles of optical antenna-designed, colloidal core/shell CdSe/CdS quantum rods deposited on silica microspheres. We obtain single-exciton emission by capitalizing on the band structure of the specific core/shell architecture that strongly localizes holes in the core, and the two-dimensional quantum confinement of electrons across the elongated shell. This creates a type-II conduction band alignment driven by coulombic repulsion that eliminates non-radiative multi-exciton Auger recombination processes, thereby inducing a large exciton–bi-exciton energy shift. Their ultra-low thresholds and single-mode, single-exciton emission make these hybrid lasers appealing for various applications, including quantum information processing. PMID:23974520

Optimized ultra-thin manganin alloy passivated fine-pitch damascene compatible bump-less Cu-Cu bonding at sub 200 °C for three-dimensional Integration applications

NASA Astrophysics Data System (ADS)

Panigrahi, Asisa Kumar; Hemanth Kumar, C.; Bonam, Satish; Ghosh, Tamal; Rama Krishna Vanjari, Siva; Govind Singh, Shiv

2018-02-01

Enhanced Cu diffusion, Cu surface passivation, and smooth surface at the bonding interface are the key essentials for high quality Cu-Cu bonding. Previously, we have demonstrated optimized 3 nm thin Manganin metal-alloy passivation from oxidation and also helps to reduce the surface roughness to about 0.8 nm which substantially led to high quality Cu-Cu bonding. In this paper, we demonstrated an ultra fine-pitch (<25 µm) Cu-Cu bonding using an optimized Manganin metal-alloy passivation. This engineered surface passivation approach led to high quality bonding at sub 200 °C temperature and 0.4 MPa. Very low specific contact resistance of 1.4 × 10-7 Ω cm2 and the defect free bonded interface is clear indication of high quality bonding for future multilayer integrations. Furthermore, electrical characterization of the bonded structure was performed under various robust conditions as per International Technology Roadmap for Semiconductors (ITRS Roadmap) in order to satisfy the stability of the bonded structure.

Hyperchaotic Dynamics for Light Polarization in a Laser Diode

NASA Astrophysics Data System (ADS)

Bonatto, Cristian

2018-04-01

It is shown that a highly randomlike behavior of light polarization states in the output of a free-running laser diode, covering the whole Poincaré sphere, arises as a result from a fully deterministic nonlinear process, which is characterized by a hyperchaotic dynamics of two polarization modes nonlinearly coupled with a semiconductor medium, inside the optical cavity. A number of statistical distributions were found to describe the deterministic data of the low-dimensional nonlinear flow, such as lognormal distribution for the light intensity, Gaussian distributions for the electric field components and electron densities, Rice and Rayleigh distributions, and Weibull and negative exponential distributions, for the modulus and intensity of the orthogonal linear components of the electric field, respectively. The presented results could be relevant for the generation of single units of compact light source devices to be used in low-dimensional optical hyperchaos-based applications.

Size effect in thermoelectric materials

NASA Astrophysics Data System (ADS)

Mao, Jun; Liu, Zihang; Ren, Zhifeng

2016-12-01

Thermoelectric applications have attracted increasing interest recently due to its capability of converting waste heat into electricity without hazardous emissions. Materials with enhanced thermoelectric performance have been reported in recent two decades. The revival of research for thermoelectric materials began in early 1990s when the size effect is considered. Low-dimensional materials with exceptionally high thermoelectric figure of merit (ZT) have been presented, which broke the limit of ZT around unity. The idea of size effect in thermoelectric materials even inspired the later nanostructuring and band engineering strategies, which effectively enhanced the thermoelectric performance of bulk materials. In this overview, the size effect in low-dimensional thermoelectric materials is reviewed. We first discuss the quantum confinement effect on carriers, including the enhancement of electronic density of states, semimetal to semiconductor transition and carrier pocket engineering. Then, the effect of assumptions on theoretical calculations is presented. Finally, the effect of phonon confinement and interface scattering on lattice thermal conductivity is discussed.

Betavoltaic Battery Conversion Efficiency Improvement Based on Interlayer Structures

NASA Astrophysics Data System (ADS)

Li, Da-Rang; Jiang, Lan; Yin, Jian-Hua; Tan, Yuan-Yuan; Lin, Nai

2012-07-01

Significant differences among the doping densities of PN junctions in semiconductors cause lattice mismatch and lattice defects that increase the recombination current of betavoltaic batteries. This extensively decreases the open circuit voltage and the short current, which results in low conversion efficiency. This study proposes P+PINN+-structure based betavoltaic batteries by adding an interlayer to typical PIN structures to improve conversion efficiency. Numerical simulations are conducted for the energy deposition of beta particles along the thickness direction in semiconductors. Based on this, 63Ni-radiation GaAs batteries with PIN and P+PINN+ structures are designed and fabricated to experimentally verify the proposed design. It turns out that the conversion efficiency of the betavoltaic battery with the proposed P+PINN+ structure is about 1.45 times higher than that with the traditional PIN structure.

Semiconductor laser using multimode interference principle

NASA Astrophysics Data System (ADS)

Gong, Zisu; Yin, Rui; Ji, Wei; Wu, Chonghao

2018-01-01

Multimode interference (MMI) structure is introduced in semiconductor laser used in optical communication system to realize higher power and better temperature tolerance. Using beam propagation method (BPM), Multimode interference laser diode (MMI-LD) is designed and fabricated in InGaAsP/InP based material. As a comparison, conventional semiconductor laser using straight single-mode waveguide is also fabricated in the same wafer. With a low injection current (about 230 mA), the output power of the implemented MMI-LD is up to 2.296 mW which is about four times higher than the output power of the conventional semiconductor laser. The implemented MMI-LD exhibits stable output operating at the wavelength of 1.52 μm and better temperature tolerance when the temperature varies from 283.15 K to 293.15 K.

Solution-processed, Self-organized Organic Single Crystal Arrays with Controlled Crystal Orientation

PubMed Central

Kumatani, Akichika; Liu, Chuan; Li, Yun; Darmawan, Peter; Takimiya, Kazuo; Minari, Takeo; Tsukagoshi, Kazuhito

2012-01-01

A facile solution process for the fabrication of organic single crystal semiconductor devices which meets the demand for low-cost and large-area fabrication of high performance electronic devices is demonstrated. In this paper, we develop a bottom-up method which enables direct formation of organic semiconductor single crystals at selected locations with desired orientations. Here oriented growth of one-dimensional organic crystals is achieved by using self-assembly of organic molecules as the driving force to align these crystals in patterned regions. Based upon the self-organized organic single crystals, we fabricate organic field effect transistor arrays which exhibit an average field-effect mobility of 1.1 cm2V−1s−1. This method can be carried out under ambient atmosphere at room temperature, thus particularly promising for production of future plastic electronics. PMID:22563523

Optical Design of Plant Canopy Measurement System and Fabrication of Two-Dimensional High-Speed Metal-Semiconductor-Metal Photodetector Arrays

NASA Technical Reports Server (NTRS)

Sarto, Anthony; VanZeghbroeck, Bart; Vanderbilt, Vern C.

1996-01-01

Electrical and optical designs for the prototype plant canopy architecture measurement system, including specified component and parts lists, are presented. Six single Metal-Semiconductor-Metal (MSM) detectors are mounted in high-speed packages.

Semiconductor devices having a recessed electrode structure

DOEpatents

Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

2015-05-26

An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

Nanoionics-Based Switches for Radio-Frequency Applications

NASA Technical Reports Server (NTRS)

Nessel, James; Lee, Richard

2010-01-01

Nanoionics-based devices have shown promise as alternatives to microelectromechanical systems (MEMS) and semiconductor diode devices for switching radio-frequency (RF) signals in diverse systems. Examples of systems that utilize RF switches include phase shifters for electronically steerable phased-array antennas, multiplexers, cellular telephones and other radio transceivers, and other portable electronic devices. Semiconductor diode switches can operate at low potentials (about 1 to 3 V) and high speeds (switching times of the order of nanoseconds) but are characterized by significant insertion loss, high DC power consumption, low isolation, and generation of third-order harmonics and intermodulation distortion (IMD). MEMS-based switches feature low insertion loss (of the order of 0.2 dB), low DC power consumption (picowatts), high isolation (>30 dB), and low IMD, but contain moving parts, are not highly reliable, and must be operated at high actuation potentials (20 to 60 V) generated and applied by use of complex circuitry. In addition, fabrication of MEMS is complex, involving many processing steps. Nanoionics-based switches offer the superior RF performance and low power consumption of MEMS switches, without need for the high potentials and complex circuitry necessary for operation of MEMS switches. At the same time, nanoionics-based switches offer the high switching speed of semiconductor devices. Also, like semiconductor devices, nanoionics-based switches can be fabricated relatively inexpensively by use of conventional integrated-circuit fabrication techniques. More over, nanoionics-based switches have simple planar structures that can easily be integrated into RF power-distribution circuits.

Ultrafast Spectral Diffusion of the First Subband Exciton in Single-Wall Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Schilling, Daniel; Hertel, Tobias

2013-03-01

The width of optical transitions in semiconductors is determined by homogeneous and inhomogeneous contributions. Here, we report on the determination of homogeneous linewidths for the first exciton subband transition and the dynamics of spectral diffusion in single-wall carbon nanotubes (SWNTs) using one- and two-dimensional time resolved spectral hole burning spectroscopy. Our investigation of highly purified semiconducting (6,5)-SWNTs suggests that room temperature homogeneous linewidths are on the order of 4 meV and are rapidly broadened by an ultrafast sub-ps spectral diffusion process. These findings are supported by our off-resonant excitation experiments where we observe sub-ps population transfer reflecting the thermal distribution of energy levels around the first subband exciton transition. The results of temperature-dependent spectral hole burning experiments between 17 K and 293 K suggest that homogeneous linewidths are due to exciton interaction with low energy optical phonons, most likely of the radial breathing mode type. In contrast, we find that inhomogeneous broadening is determined by an electronic degree of freedom such as ultrafast intra-tube exciton diffusion which is characteristic and unique for excitons in these one-dimensional semiconductors.

GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

NASA Astrophysics Data System (ADS)

Onen, A.; Kecik, D.; Durgun, E.; Ciraci, S.

2016-02-01

Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g -GaN ) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g -GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g -GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g -GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g -GaN are preserved when g -GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g -GaN , is found to be an excellent substrate for growing g -GaN . Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g -GaN , and they can display electronic and optical properties that can be controlled by the number of g -GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g -GaN layers.

New hybrid lead iodides: From one-dimensional chain to two-dimensional layered perovskite structure

NASA Astrophysics Data System (ADS)

Xiong, Kecai; Liu, Wei; Teat, Simon J.; An, Litao; Wang, Hao; Emge, Thomas J.; Li, Jing

2015-10-01

Two new hybrid lead halides (H2BDA)[PbI4] (1) (H2BDA=1,4-butanediammonium dication) and (HNPEIM)[PbI3] (2) (HNPEIM=N-​phenyl-ethanimidamidine cation) have been synthesized and structurally characterized. X-ray diffraction analyses reveal that compound 1 features a two-dimensional corner-sharing perovskite layer whereas compound 2 contains one-dimensional edge-sharing double chains. The N-​phenyl-ethanimidamidine cation within compound 2 was generated in-situ under solvothermal conditions. The optical absorption spectra collected at room temperature suggest that both compounds are semiconductors having direct band gaps, with estimated values of 2.64 and 2.73 eV for 1 and 2, respectively. Results from the density functional theory (DFT) calculations are consistent with the experimental data. Density of states (DOS) analysis reveals that in both compounds 1 and 2, the energy states in the valence band maximum region are iodine 5p atomic orbitals with a small contribution from lead 6s, while in the region of conduction band minimum, the major contributions are from the inorganic (Pb 6p atomic orbitals) and organic components (C and N 2p atomic orbitals) in compound 1 and 2, respectively.

Estimation of carrier mobility and charge behaviors of organic semiconductor films in metal-insulator-semiconductor diodes consisting of high-k oxide/organic semiconductor double layers

NASA Astrophysics Data System (ADS)

Chosei, Naoya; Itoh, Eiji

2018-02-01

We have comparatively studied the charge behaviors of organic semiconductor films based on charge extraction by linearly increasing voltage in a metal-insulator-semiconductor (MIS) diode structure (MIS-CELIV) and by classical capacitance-voltage measurement. The MIS-CELIV technique allows the selective measurement of electron and hole mobilities of n- and p-type organic films with thicknesses representative of those of actual devices. We used an anodic oxidized sputtered Ta or Hf electrode as a high-k layer, and it effectively blocked holes at the insulator/semiconductor interface. We estimated the hole mobilities of the polythiophene derivatives regioregular poly(3-hexylthiophene) (P3HT) and poly(3,3‧‧‧-didodecylquarterthiophene) (PQT-12) before and after heat treatment in the ITO/high-k/(thin polymer insulator)/semiconductor/MoO3/Ag device structure. The hole mobility of PQT-12 was improved from 1.1 × 10-5 to 2.1 × 10-5 cm2 V-1 s-1 by the heat treatment of the device at 100 °C for 30 min. An almost two orders of magnitude higher mobility was obtained in MIS diodes with P3HT as the p-type layer. We also determined the capacitance from the displacement current in MIS diodes at a relatively low-voltage sweep, and it corresponded well to the classical capacitance-voltage and frequency measurement results.

Fiber optic coupling of a microlens conditioned, stacked semiconductor laser diode array

DOEpatents

Beach, Raymond J.; Benett, William J.; Mills, Steven T.

1997-01-01

The output radiation from the two-dimensional aperture of a semiconductor laser diode array is efficiently coupled into an optical fiber. The two-dimensional aperture is formed by stacking individual laser diode bars on top of another in a "rack and stack" configuration. Coupling into the fiber is then accomplished using individual microlenses to condition the output radiation of the laser diode bars. A lens that matches the divergence properties and wavefront characteristics of the laser light to the fiber optic is used to focus this conditioned radiation into the fiber.

Semiconductor Cubing

NASA Technical Reports Server (NTRS)

1996-01-01

Through Goddard Space Flight Center and Jet Propulsion Laboratory Small Business Innovation Research contracts, Irvine Sensors developed a three-dimensional memory system for a spaceborne data recorder and other applications for NASA. From these contracts, the company created the Memory Short Stack product, a patented technology for stacking integrated circuits that offers higher processing speeds and levels of integration, and lower power requirements. The product is a three-dimensional semiconductor package in which dozens of integrated circuits are stacked upon each other to form a cube. The technology is being used in various computer and telecommunications applications.

Ferroelectric polarization-controlled two-dimensional electron gas in ferroelectric/AlGaN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Kong, Y. C.; Xue, F. S.; Zhou, J. J.; Li, L.; Chen, C.; Li, Y. R.

2009-06-01

The control effect of the ferroelectric polarization on the two-dimensional electron gas (2DEG) in a ferroelectric/AlGaN/GaN metal-ferroelectric-semiconductor (MFS) structure is theoretically analyzed by a self-consistent approach. With incorporating the hysteresis nature of the ferroelectric into calculation, the nature of the control effect is disclosed, where the 2DEG density is depleted/restored after poling/depoling operation on the MFS structure. The orientation of the ferroelectric polarization is clarified to be parallel to that of the AlGaN barrier, which, based on an electrostatics analysis, is attributed to the pinning effect of the underlying polarization. Reducing the thickness of the AlGaN barrier from 25 nm to 20 nm leads to an improved control modulation of the 2DEG density from 36.7% to 54.1%.

Plasmon-exciton polaritons in two-dimensional semiconductor/metal interfaces

NASA Astrophysics Data System (ADS)

Gonçalves, P. A. D.; Bertelsen, L. P.; Xiao, Sanshui; Mortensen, N. Asger

2018-01-01

The realization and control of polaritons is of paramount importance in the prospect of novel photonic devices. Here, we investigate the emergence of plasmon-exciton polaritons in hybrid structures consisting of a two-dimensional transition-metal dichalcogenide (TMDC) deposited onto a metal substrate or coating a metallic thin film. We determine the polaritonic spectrum and show that, in the former case, the addition of a top dielectric layer and, in the latter case, the thickness of the metal film can be used to tune and promote plasmon-exciton interactions well within the strong-coupling regime. Our results demonstrate that Rabi splittings exceeding 100 meV can readily be achieved in planar dielectric/TMDC/metal structures under ambient conditions. We thus believe that this Rapid Communication provides a simple and intuitive picture to tailor strong coupling in plexcitonics with potential applications for engineering compact photonic devices with tunable optical properties.

Structural complexity and wide application of two-dimensional S/O type antimonene

NASA Astrophysics Data System (ADS)

Li, T. T.; He, C.; Zhang, W. X.

2018-05-01

Inspired by stable two-dimensional antimonene phases, two new allotropes (S/O and tricycle) antimonenes have been predicted by first-principles calculations in this paper. S/O type antimonene possesses remarkably thermodynamical and dynamical stability, which are comparable to that of buckled type antimonene. The results indicate that S/O type antimonene is a direct band gap semiconductor with a band gap of 2.314 eV and the electronic properties could be effectively tuned by the in-plane strain. In order to explore the potential application, the mechanical properties and optical properties of S/O type antimonene are also extensively studied. It is found the S/O type antimonene is an anisotropic material by the method of analyzing the linear Poisson's ratios and the phonon band structure. These systematical analyses show that S/O type antimonene is a new 2D material with tunable electronic properties, excellent mechanical and optical properties.

Three-dimensional carbon allotropes comprising phenyl rings and acetylenic chains in sp+ sp 2 hybrid networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian -Tao; Chen, Changfeng; Li, Han -Dong

Here, we here identify by ab initio calculations a new type of three-dimensional (3D) carbon allotropes that consist of phenyl rings connected by linear acetylenic chains in sp+ sp 2 bonding networks. These structures are constructed by inserting acetylenic or diacetylenic bonds into an all sp 2-hybridized rhombohedral polybenzene lattice, and the resulting 3D phenylacetylene and phenyldiacetylene nets comprise a 12-atom and 18-atom rhombohedral primitive unit cells R - 3m symmetry, which are characterized as the 3D chiral crystalline modification of 2D graphyne and graphdiyne, respectively. Simulated phonon spectra reveal that these structures are dynamically stable. Electronic band calculations indicatemore » that phenylacetylene is metallic, while phenyldiacetylene is a semiconductor with an indirect band gap of 0.58 eV. The present results establish a new type of carbon phases and offer insights into their outstanding structural and electronic properties.« less

Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation.

PubMed

Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn

2016-03-30

Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.

Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation

PubMed Central

Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn

2016-01-01

Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors. PMID:27026070

Three-dimensional carbon allotropes comprising phenyl rings and acetylenic chains in sp+ sp 2 hybrid networks

DOE PAGES

Wang, Jian -Tao; Chen, Changfeng; Li, Han -Dong; ...

2016-04-18

Here, we here identify by ab initio calculations a new type of three-dimensional (3D) carbon allotropes that consist of phenyl rings connected by linear acetylenic chains in sp+ sp 2 bonding networks. These structures are constructed by inserting acetylenic or diacetylenic bonds into an all sp 2-hybridized rhombohedral polybenzene lattice, and the resulting 3D phenylacetylene and phenyldiacetylene nets comprise a 12-atom and 18-atom rhombohedral primitive unit cells R - 3m symmetry, which are characterized as the 3D chiral crystalline modification of 2D graphyne and graphdiyne, respectively. Simulated phonon spectra reveal that these structures are dynamically stable. Electronic band calculations indicatemore » that phenylacetylene is metallic, while phenyldiacetylene is a semiconductor with an indirect band gap of 0.58 eV. The present results establish a new type of carbon phases and offer insights into their outstanding structural and electronic properties.« less

Three-Dimensional CdS/Au Butterfly Wing Scales with Hierarchical Rib Structures for Plasmon-Enhanced Photocatalytic Hydrogen Production.

PubMed

Fang, Jing; Gu, Jiajun; Liu, Qinglei; Zhang, Wang; Su, Huilan; Zhang, Di

2018-06-13

Localized surface plasmon resonance (LSPR) of plasmonic metals (e.g., Au) can help semiconductors improve their photocatalytic hydrogen (H 2 ) production performance. However, an artificial synthesis of hierarchical plasmonic structures down to nanoscales is usually difficult. Here, we adopt the butterfly wing scales from Morpho didius to fabricate three-dimensional (3D) CdS/Au butterfly wing scales for plasmonic photocatalysis. The as-prepared materials well-inherit the pristine hierarchical biostructures. The 3D CdS/Au butterfly wing scales exhibit a high H 2 production rate (221.8 μmol·h -1 within 420-780 nm), showing a 241-fold increase over the CdS butterfly wing scales. This is attributed to the effective potentiation effect of LSPR introduced by multilayer metallic rib structures and a good interface bonding state between Au and CdS nanoparticles. Thus, our study provides a relatively simple method to learn from nature and inspiration for preparing highly efficient plasmonic photocatalysts.

Hydrogen-terminated diamond vertical-type metal oxide semiconductor field-effect transistors with a trench gate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inaba, Masafumi, E-mail: inaba-ma@ruri.waseda.jp; Muta, Tsubasa; Kobayashi, Mikinori

2016-07-18

The hydrogen-terminated diamond surface (C-H diamond) has a two-dimensional hole gas (2DHG) layer independent of the crystal orientation. A 2DHG layer is ubiquitously formed on the C-H diamond surface covered by atomic-layer-deposited-Al{sub 2}O{sub 3}. Using Al{sub 2}O{sub 3} as a gate oxide, C-H diamond metal oxide semiconductor field-effect transistors (MOSFETs) operate in a trench gate structure where the diamond side-wall acts as a channel. MOSFETs with a side-wall channel exhibit equivalent performance to the lateral C-H diamond MOSFET without a side-wall channel. Here, a vertical-type MOSFET with a drain on the bottom is demonstrated in diamond with channel current modulationmore » by the gate and pinch off.« less

Quantum size effects in layered VX{sub 2} (X = S, Se) materials: Manifestation of metal to semimetal or semiconductor transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wasey, A. H. M. Abdul; Chakrabarty, Soubhik; Das, G. P., E-mail: msgpd@iacs.res.in

2015-02-14

Most of the two dimensional (2D) transition metal dichalcogenides (TMDC) are nonmagnetic in pristine form. However, 2D pristine VX{sub 2} (X = S, Se, Te) materials are found to be ferromagnetic. Using spin polarized density functional theory (DFT) calculations, we have studied the electronic, magnetic, and surface properties of this class of materials in both trigonal prismatic H- and octahedral T-phase. Our calculations reveal that they exhibit materially different properties in those two polymorphs. Most importantly, detailed investigation of electronic structure explored the quantum size effect in H-phase of these materials thereby leading to metal to semimetal (H-VS{sub 2}) or semiconductor (H-VSe{submore » 2}) transition when downsizing from bilayer to corresponding monolayer.« less

Standardization of Schwarz-Christoffel transformation for engineering design of semiconductor and hybrid integrated-circuit elements

NASA Astrophysics Data System (ADS)

Yashin, A. A.

1985-04-01

A semiconductor or hybrid structure into a calculable two-dimensional region mapped by the Schwarz-Christoffel transformation and a universal algorithm can be constructed on the basis of Maxwell's electro-magnetic-thermal similarity principle for engineering design of integrated-circuit elements. The design procedure involves conformal mapping of the original region into a polygon and then the latter into a rectangle with uniform field distribution, where conductances and capacitances are calculated, using tabulated standard mapping functions. Subsequent synthesis of a device requires inverse conformal mapping. Devices adaptable as integrated-circuit elements are high-resistance film resistors with periodic serration, distributed-resistance film attenuators with high transformation ratio, coplanar microstrip lines, bipolar transistors, directional couplers with distributed coupling to microstrip lines for microwave bulk devices, and quasirregular smooth matching transitions from asymmetric to coplanar microstrip lines.

Selective control of electron and hole tunneling in 2D assembly

PubMed Central

Chu, Dongil; Lee, Young Hee; Kim, Eun Kyu

2017-01-01

Recent discoveries in the field of two-dimensional (2D) materials have led to the demonstration of exotic devices. Although they have new potential applications in electronics, thermally activated transport over a metal/semiconductor barrier sets physical subthermionic limitations. The challenge of realizing an innovative transistor geometry that exploits this concern remains. A new class of 2D assembly (namely, “carristor”) with a configuration similar to the metal-insulator-semiconductor structure is introduced in this work. Superior functionalities, such as a current rectification ratio of up to 400,000 and a switching ratio of higher than 106 at room temperature, are realized by quantum-mechanical tunneling of majority and minority carriers across the barrier. These carristors have a potential application as the fundamental building block of low–power consumption electronics. PMID:28439554

Understanding the Vapor-Liquid-Solid and Vapor-Solid-Solid Mechanisms of Si Nanowire Growth to Synthetically Encode Precise Nanoscale Morphology

NASA Astrophysics Data System (ADS)

Pinion, Christopher William

Precise patterning of semiconductor materials utilizing top-down lithographic techniques is integral to the advanced electronics we use on a daily basis. However, continuing development of these lithographic technologies often results in the trade-off of either high cost or low throughput, and three-dimensional (3D) patterning can be difficult to achieve. Bottom-up, chemical methods to control the 3D nanoscale morphology of semiconductor nanostructures have received significant attention as a complementary technique. Semiconductor nanowires, nanoscale filaments of semiconductor material 10-500 nm in diameter and 1-50 microns in length, are an especially promising platform because the wire composition can be modulated during growth and the high aspect ratio, one-dimensional structure enables integration in a range of devices. In this thesis, we first report a bottom-up method to break the conventional "wire" symmetry and synthetically encode a high-resolution array of arbitrary shapes along the nanowire growth axis. Rapid modulation of phosphorus doping combined with selective wet-chemical etching enables morphological features as small as 10 nm to be patterned over wires more than 50 ?m in length. Next, our focus shifts to more fundamental studies of the nanowire synthetic mechanisms. We presented comprehensive experimental measurements on the growth rate of Au catalyzed Si nanowires and developed a kinetic model of vapor-liquid-solid growth. Our analysis revealed an abrupt transition from a diameter-independent growth rate that is limited by incorporation to a diameter-dependent growth rate that is limited by crystallization. While investigating the vapor-liquid-solid mechanism, we noticed instances of unique catalyst behavior. Upon further study, we showed that it is possible to instantaneously and reversibly switch the phase of the catalyst between a liquid and superheated solid state under isothermal conditions above the eutectic temperature. The solid catalyst induces a vapor-solid-solid growth mechanism, which provides atomic-level control of dopant atoms in the nanowire. Finally, we explored a promising application of nanowires by investigating the potential for complex silicon nanowires to serve as a platform for next-generation photovoltaic devices. We reviewed the synthesis, electrical, and optical characteristics of core/shell Si nanowires that are sub-wavelength in diameter and contain radial p-n junctions. We highlighted the unique features of these nanowires, such as optical antenna effects that concentrate light and intense built-in electric fields that enable ultrafast charge-carrier separation. Based on these observations we advocate for a paradigm in which nanowires are arranged in periodic horizontal arrays to form ultrathin devices.

Fabrication of smooth patterned structures of refractory metals, semiconductors, and oxides via template stripping.

PubMed

Park, Jong Hyuk; Nagpal, Prashant; McPeak, Kevin M; Lindquist, Nathan C; Oh, Sang-Hyun; Norris, David J

2013-10-09

The template-stripping method can yield smooth patterned films without surface contamination. However, the process is typically limited to coinage metals such as silver and gold because other materials cannot be readily stripped from silicon templates due to strong adhesion. Herein, we report a more general template-stripping method that is applicable to a larger variety of materials, including refractory metals, semiconductors, and oxides. To address the adhesion issue, we introduce a thin gold layer between the template and the deposited materials. After peeling off the combined film from the template, the gold layer can be selectively removed via wet etching to reveal a smooth patterned structure of the desired material. Further, we demonstrate template-stripped multilayer structures that have potential applications for photovoltaics and solar absorbers. An entire patterned device, which can include a transparent conductor, semiconductor absorber, and back contact, can be fabricated. Since our approach can also produce many copies of the patterned structure with high fidelity by reusing the template, a low-cost and high-throughput process in micro- and nanofabrication is provided that is useful for electronics, plasmonics, and nanophotonics.

Twenty years of molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Cho, A. Y.

1995-05-01

The term "molecular beam epitaxy" (MBE) was first used in one of our crystal growth papers in 1970, after having conducted extensive surface physics studies in the late 1960's of the interaction of atomic and molecular beams with solid surfaces. The unique feature of MBE is the ability to prepare single crystal layers with atomic dimensional precision. MBE sets the standard for epitaxial growth and has made possible semiconductor structures that could not be fabricated with either naturally existing materials or by other crystal growth techniques. MBE led the crystal growth technologies when it prepared the first semiconductor quantum well and superlattice structures that gave unexpected and exciting electrical and optical properties. For example, the discovery of the fractional quantized Hall effect. It brought experimental quantum physics to the classroom, and practically all major universities throughout the world are now equipped with MBE systems. The fundamental principles demonstrated by the MBE growth of III-V compound semiconductors have also been applied to the growth of group IV, II-VI, metal, and insulating materials. For manufacturing, the most important criteria are uniformity, precise control of the device structure, and reproducibility. MBE has produced more lasers (3 to 5 million per month for compact disc application) than any other crystal growth technique in the world. New directions for MBE are to incorporate in-situ, real-time monitoring capabilities so that complex structures can be precisely "engineered". In the future, as environmental concerns increase, the use of toxic arsine and phosphine may be limited. Successful use of valved cracker cells for solid arsenic and phosphorus has already produced InP based injection lasers.

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE PAGES

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony; ...

2017-11-07

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Bi-continuous Multi-component Nanocrystal Superlattices for Solar Energy Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kagan, Cherie; Murray, Christopher; Kikkawa, James

2017-06-14

Our SISGR program studied an emerging class of nanomaterials wherein different combinations of semiconductor or semiconductor and plasmonic nanocrystals (NCs) are self-assembled into three-dimensional multi-component superlattices. The NC assemblies were designed to form bicontinuous semiconductor NC sublattices with type-II energy offsets to drive charge separation onto electron and hole transporting sublattices for collection and introduce plasmonic NCs to increase solar absorption and charge separation. Our group is expert in synthesizing and assembling an extraordinary variety of artificial systems by tailoring the NC building blocks and the superlattice unit cell geometry. Under this DOE BES Materials Chemistry program, we introduced chemicalmore » methods to control inter-particle distance and to dope NC assemblies, which enabled our demonstration of strong electronic communication between NCs and the use of NC thin films as electronic materials. We synthesized, assembled and structurally, spectroscopically, and electrically probed NC superlattices to understand and manipulate the flow of energy and charge toward discovering the design rules and optimizing these complex architectures to create materials that efficiently convert solar radiation into electricity.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures.

PubMed

Cherukara, Mathew J; Sasikumar, Kiran; DiChiara, Anthony; Leake, Steven J; Cha, Wonsuk; Dufresne, Eric M; Peterka, Tom; McNulty, Ian; Walko, Donald A; Wen, Haidan; Sankaranarayanan, Subramanian K R S; Harder, Ross J

2017-12-13

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. In this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplay of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.

Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures.

PubMed

Wan, Zhong; Kazakov, Aleksandr; Manfra, Michael J; Pfeiffer, Loren N; West, Ken W; Rokhinson, Leonid P

2015-06-11

Search for Majorana fermions renewed interest in semiconductor-superconductor interfaces, while a quest for higher-order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, such as a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures and development of highly transparent semiconductor-superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 μm, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields (>16 T) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two-dimensional electron gas at high magnetic fields.

Semiconductor-like behavior in superconducting Nb/Al films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greco, M.; Menichetti, E.; Rinaudo, G.

1999-04-20

The authors report here the experimental evidence of semiconductor-superconductor transitions in relatively thick Nb/Al structures. The temperature dependence of resistivity {rho}(T) shows a sharp superconducting transition followed by either a normal metallic behavior in low-resistivity samples, or a semiconducting behavior when the sample resistivity at 10 K is above 100 {mu}{Omega} cm. The authors discuss here the fabrication conditions and the electron localization regime associated with the measured {rho}(T) dependence.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Transient heat conduction in laser diodes

NASA Astrophysics Data System (ADS)

Enders, P.; Galley, J.

1988-11-01

The dynamics of heat transfer in stripe GaAlAs laser diodes is investigated by solving the linear diffusion equation for a quasitwo-dimensional multilayer structure. The calculations are rationalized drastically by the transfer matrix method and also using for the first time the asymptotes of the decay constants. Special attention is given to the convergence of the Fourier series. A comparison with experimental results reveals however that this is essentially the Stefan problem (with moving boundary conditions).

Ballistic transport in nanowires through non-magnetic or magnetic cavity

NASA Astrophysics Data System (ADS)

Nonoyama, Shinji; Honma, Yukari; Ono, Miyuki; Nakamura, Atsunobu

2015-07-01

Ballistic transport phenomena through a region containing a cavity in a quasi-one-dimensional quantum nanowire are investigated. Conductance curves calculated as a function of a structural parameter show quantum interference effects on transport clearly. In a special geometry, very narrow periodic dips, which are attributable to the anti-resonance, appear on the conductance curve. The nature of the virtual bound state resulting in the anti-resonance is studied in detail. Electron conductions through a small dilute magnetic semiconductor are also investigated.

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, John R.

1986-01-01

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, J.R.

1984-10-10

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliev, Ziya S., E-mail: ziyasaliev@gmail.com; Institute of Physics, ANAS, H.Javid ave. 131, AZ1143 Baku; Donostia International Physics Center

Single crystals of the ternary copper compounds CuTlS and CuTlSe have been successfully grown from stoichiometric melt by using vertical Bridgman-Stockbarger method. The crystal structure of the both compounds has been determined by powder and single crystal X-Ray diffraction. They crystallize in the PbFCl structure type with two formula units in the tetragonal system, space group P4/nmm, a=3.922(2); c=8.123(6); Z=2 and a=4.087(6); c=8.195(19) Å; Z=2, respectively. The band structure of the reported compounds has been analyzed by means of full-potential linearized augmented plane-wave (FLAPW) method based on the density functional theory (DFT). Both compounds have similar band structures and aremore » narrow-gap semiconductors with indirect band gap. The resistivity measurements agree with a semiconductor behavior although anomalies are observed at low temperature. - Graphical abstract: The crystal structures of CuTl and CuTlSe are isostructural with the PbFCl-type and the superconductor LiFeAs-type tetragonal structure. The band structure calculations confirmed that they are narrow-gap semiconductors with indirect band gaps of 0.326 and 0.083 eV. The resistivity measurements, although confirming the semiconducting behavior of both compounds exhibit unusual anomalies at low temperatures. - Highlights: • Single crystals of CuTlS and CuTlSe have been successfully grown by Bridgman-Stockbarger method. • The crystal structure of the both compounds has been determined by single crystal XRD. • The band structure of the both compounds has been analyzed based on the density functional theory (DFT). • The resistivity measurements have been carried out from room temperature down to 10 K.« less

Oxide-mediated recovery of field-effect mobility in plasma-treated MoS2

PubMed Central

Jadwiszczak, Jakub; O’Callaghan, Colin; Zhou, Yangbo; Fox, Daniel S.; Weitz, Eamonn; Keane, Darragh; Cullen, Conor P.; O’Reilly, Ian; Downing, Clive; Shmeliov, Aleksey; Maguire, Pierce; Gough, John J.; McGuinness, Cormac; Ferreira, Mauro S.; Bradley, A. Louise; Boland, John J.; Duesberg, Georg S.; Nicolosi, Valeria; Zhang, Hongzhou

2018-01-01

Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoOx) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoOx will serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures. PMID:29511736

Low carrier semiconductor like behavior in Lu3Ir4Ge13 single crystal

NASA Astrophysics Data System (ADS)

Kumar, Anil; Matteppanavar, Shidaling; Thamizhavel, A.; Ramakrishnan, S.

2018-04-01

Single crystal of Lu3Ir4Ge13 crystallizing in the Yb3Rh4Sn13-type cubic crystal structure has been grown by Czochralski method in a tetra-arc furnace. In this paper we report on the crystal structure, magnetic and transport properties of Lu3Ir4Ge13. The analysis of the powder x-ray diffraction (XRD) studies revealed that Lu3Ir4Ge13 crystallizes in a cubic structure with the space group Pm-3n, no. 223. The lattice parameter was obtained from the Rietveld refinement of the room temperature XRD data which amounts to 8.904 (3) Å with low R factors. The temperature dependence of the resistivity exhibited semiconductor like behavior till 1.8 K, with a broad hump around 15 - 62 K. This hump was observed in both warming and cooling cycle with a very small hysteresis, it may be due to the existence of structural transition from high - low symmetry. The temperature dependent magnetization data shows the diamagnetic behavior with an anomaly around 70 K, which is well supported by the derivative of resistivity data.

A superhard sp3 microporous carbon with direct bandgap

NASA Astrophysics Data System (ADS)

Pan, Yilong; Xie, Chenlong; Xiong, Mei; Ma, Mengdong; Liu, Lingyu; Li, Zihe; Zhang, Shuangshuang; Gao, Guoying; Zhao, Zhisheng; Tian, Yongjun; Xu, Bo; He, Julong

2017-12-01

Carbon allotropes with distinct sp, sp2, and sp3 hybridization possess various different properties. Here, a novel all-sp3 hybridized tetragonal carbon, namely the P carbon, was predicted by the evolutionary particle swarm structural search. It demonstrated a low density among all-sp3 carbons, due to the corresponding distinctive microporous structure. P carbon is thermodynamically stable than the known C60 and could be formed through the single-walled carbon nanotubes (SWCNTs) compression. P carbon is a direct bandgap semiconductor displaying a strong and superhard nature. The unique combination of electrical and mechanical properties constitutes P carbon a potential superhard material for semiconductor industrial fields.

Method for formation of thin film transistors on plastic substrates

DOEpatents

Carey, Paul G.; Smith, Patrick M.; Sigmon, Thomas W.; Aceves, Randy C.

1998-10-06

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The process relies on techniques for depositing semiconductors, dielectrics, and metals at low temperatures; crystallizing and doping semiconductor layers in the TFT with a pulsed energy source; and creating top-gate self-aligned as well as back-gate TFT structures. The process enables the fabrication of amorphous and polycrystalline channel silicon TFTs at temperatures sufficiently low to prevent damage to plastic substrates. The process has use in large area low cost electronics, such as flat panel displays and portable electronics.

Correlated Electrons in Reduced Dimensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bonesteel, Nicholas E

2015-01-31

This report summarizes the work accomplished under the support of US DOE grant # DE-FG02-97ER45639, "Correlated Electrons in Reduced Dimensions." The underlying hypothesis of the research supported by this grant has been that studying the unique behavior of correlated electrons in reduced dimensions can lead to new ways of understanding how matter can order and how it can potentially be used. The systems under study have included i) fractional quantum Hall matter, which is realized when electrons are confined to two-dimensions and placed in a strong magnetic field at low temperature, ii) one-dimensional chains of spins and exotic quasiparticle excitationsmore » of topologically ordered matter, and iii) electrons confined in effectively ``zero-dimensional" semiconductor quantum dots.« less

Microscopic study on the carrier distribution in optoelectronic device structures: experiment and modeling

NASA Astrophysics Data System (ADS)

Huang, Wenchao; Xia, Hui; Wang, Shaowei; Deng, Honghai; Wei, Peng; Li, Lu; Liu, Fengqi; Li, Zhifeng; Li, Tianxin

2011-12-01

Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) both are capable of mapping the 2-demensional carrier distribution in semiconductor device structures, which is essential in determining their electrical and optoelectronic performances. In this work, cross-sectional SCM1,2 is used to study the InGaAs/InP P-i-N junctions prepared by area-selective p-type diffusion. The diffusion lengths in the depth as well as the lateral directions are obtained for junctions under different window sizes in mask, which imply that narrow windows may result in shallow p-n junctions. The analysis is beneficial to design and fabricate focal plane array of near infrared photodetectors with high duty-cycle and quantum efficiency. On the other hand, SSRM provides unparalleled spatial resolution (<10 nm) in electrical characterization3 that is demanded for studying low-dimensional structures. However, to derive the carrier density from the measured local conductance in individual quantum structures, reliable model for SSRM is necessary but still not well established. Based on the carrier concentration related transport mechanisms, i.e. thermionic emission and thermionic field emission4,5, we developed a numerical model for the tip-sample Schottky contact4. The calculation is confronted with SSRM study on the dose-calibrated quantum wells (QWs).

Integration of SrBi2Ta2O9 thin films for high density ferroelectric random access memory

NASA Astrophysics Data System (ADS)

Wouters, D. J.; Maes, D.; Goux, L.; Lisoni, J. G.; Paraschiv, V.; Johnson, J. A.; Schwitters, M.; Everaert, J.-L.; Boullart, W.; Schaekers, M.; Willegems, M.; Vander Meeren, H.; Haspeslagh, L.; Artoni, C.; Caputa, C.; Casella, P.; Corallo, G.; Russo, G.; Zambrano, R.; Monchoix, H.; Vecchio, G.; Van Autryve, L.

2006-09-01

Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures.

Cs 2 Hg 3 S 4 : A Low-Dimensional Direct Bandgap Semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Islam, Saiful M.; Vanishri, S.; Li, Hao

2015-01-13

Cs2Hg3S4 was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs2S4. Cs2Hg3S4 crystallizes in the Ibam spacegroup with a = 6.278(1) angstrom, b = 11.601(2) angstrom, and c = 14.431(3)angstrom; d(calc) = 6.29 g/cm(3). Its crystal structure consists of straight chains of [Hg3S4](n)(2n-) that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at 1.56 x 10(-5), 2.79more » x10(-5), and 3.04 x 10(-5) K-1, respectively. Large single-crystals up to similar to 5 cm in length and similar to 1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs2Hg3S4 gave resistivity rho of >= 10(8) Omega.cm and carrier mobility-lifetime (mu tau) products of 4.2 x 10(-4) and 5.82 x 10(-5) cm(2) V-1 for electrons and holes, respectively. Cs2Hg3S4 is a semiconductor with a bandgap E-g similar to 2.8 eV and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd-Scuseria-Ernzerhof (HSE) formalism indicate a direct bandgap of 2.81 eV at Gamma. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a much less dispersive and more anisotropic sulfur orbital-based band.« less

Two-dimensional collective electron magnetotransport, oscillations, and chaos in a semiconductor superlattice

NASA Astrophysics Data System (ADS)

Bonilla, L. L.; Carretero, M.; Segura, A.

2017-12-01

When quantized, traces of classically chaotic single-particle systems include eigenvalue statistics and scars in eigenfuntions. Since 2001, many theoretical and experimental works have argued that classically chaotic single-electron dynamics influences and controls collective electron transport. For transport in semiconductor superlattices under tilted magnetic and electric fields, these theories rely on a reduction to a one-dimensional self-consistent drift model. A two-dimensional theory based on self-consistent Boltzmann transport does not support that single-electron chaos influences collective transport. This theory agrees with existing experimental evidence of current self-oscillations, predicts spontaneous collective chaos via a period doubling scenario, and could be tested unambiguously by measuring the electric potential inside the superlattice under a tilted magnetic field.

Two-dimensional collective electron magnetotransport, oscillations, and chaos in a semiconductor superlattice.

PubMed

Bonilla, L L; Carretero, M; Segura, A

2017-12-01

When quantized, traces of classically chaotic single-particle systems include eigenvalue statistics and scars in eigenfuntions. Since 2001, many theoretical and experimental works have argued that classically chaotic single-electron dynamics influences and controls collective electron transport. For transport in semiconductor superlattices under tilted magnetic and electric fields, these theories rely on a reduction to a one-dimensional self-consistent drift model. A two-dimensional theory based on self-consistent Boltzmann transport does not support that single-electron chaos influences collective transport. This theory agrees with existing experimental evidence of current self-oscillations, predicts spontaneous collective chaos via a period doubling scenario, and could be tested unambiguously by measuring the electric potential inside the superlattice under a tilted magnetic field.

Semiconductor wire array structures, and solar cells and photodetectors based on such structures

DOEpatents

Kelzenberg, Michael D.; Atwater, Harry A.; Briggs, Ryan M.; Boettcher, Shannon W.; Lewis, Nathan S.; Petykiewicz, Jan A.

2014-08-19

A structure comprising an array of semiconductor structures, an infill material between the semiconductor materials, and one or more light-trapping elements is described. Photoconverters and photoelectrochemical devices based on such structure also described.

Viscous magnetoresistance of correlated electron liquids

NASA Astrophysics Data System (ADS)

Levchenko, Alex; Xie, Hong-Yi; Andreev, A. V.

2017-03-01

We develop a theory of magnetoresistance of two-dimensional electron systems in a smooth disorder potential in the hydrodynamic regime. Our theory applies to two-dimensional semiconductor structures with strongly correlated carriers when the mean free path due to electron-electron collisions is sufficiently short. The dominant contribution to magnetoresistance arises from the modification of the flow pattern by the Lorentz force, rather than the magnetic field dependence of the kinetic coefficients of the electron liquid. The resulting magnetoresistance is positive and quadratic at weak fields. Although the resistivity is governed by both the viscosity and thermal conductivity of the electron fluid, the magnetoresistance is controlled by the viscosity only. This enables the extraction of viscosity of the electron liquid from magnetotransport measurements.

Semiconductor structure and recess formation etch technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Bin; Sun, Min; Palacios, Tomas Apostol

2017-02-14

A semiconductor structure has a first layer that includes a first semiconductor material and a second layer that includes a second semiconductor material. The first semiconductor material is selectively etchable over the second semiconductor material using a first etching process. The first layer is disposed over the second layer. A recess is disposed at least in the first layer. Also described is a method of forming a semiconductor structure that includes a recess. The method includes etching a region in a first layer using a first etching process. The first layer includes a first semiconductor material. The first etching processmore » stops at a second layer beneath the first layer. The second layer includes a second semiconductor material.« less

Zinc Sulphide Overlayer Two-Dimensional Photonic Crystal for Enhanced Extraction of Light from a Micro Cavity Light-Emitting Diode

NASA Astrophysics Data System (ADS)

Mastro, Michael A.; Kim, Chul Soo; Kim, Mijin; Caldwell, Josh; Holm, Ron T.; Vurgaftman, Igor; Kim, Jihyun; Eddy, Charles R., Jr.; Meyer, Jerry R.

2008-10-01

A two-dimensional (2D) ZnS photonic crystal was deposited on the surface of a one-dimensional (1D) III-nitride micro cavity light-emitting diode (LED), to intermix the light extraction features of both structures (1D+2D). The deposition of an ideal micro-cavity optical thickness of ≈λ/2 is impractical for III-nitride LEDs, and in realistic multi-mode devices a large fraction of the light is lost to internal refraction as guided light. Therefore, a 2D photonic crystal on the surface of the LED was used to diffract and thus redirect this guided light out of the semiconductor over several hundred microns. Additionally, the employment of a post-epitaxy ZnS 2D photonic crystal avoided the typical etching into the GaN:Mg contact layer, a procedure which can cause damage to the near surface.

Theoretical study in carrier mobility of two-dimensional materials

NASA Astrophysics Data System (ADS)

Huang, R.

2017-09-01

Recently, the theoretical prediction on carrier mobility of two-dimensional (2D) materials has aroused wild attention. At present, there is still a large gap between the theoretical prediction and the device performance of the semiconductor based on the 2D layer semiconductor materials such as graphene. It is particularly important to theoretically design and screen the high-performance 2D layered semiconductor materials with suitable band gap and high carrier mobility. This paper introduces some 2D materials with fine properties and deduces the formula for mobility of the isotropic materials on the basis of the deformation potential theory and Fermic golden rule under acoustic phonon scattering conditions, and then discusses the carrier mobility of anisotropic materials with Dirac cones. We point out the misconceptions in the existing literature and discuss the correct ones.

Metal-organic frameworks for thermoelectric energy-conversion applications

DOE PAGES

Talin, Albert Alec; Jones, Reese E.; Hopkins, Patrick E.

2016-11-07

Motivated by low cost, low toxicity, mechanical flexibility, and conformability over complex shapes, organic semiconductors are currently being actively investigated as thermoelectric (TE) materials to replace the costly, brittle, and non-eco-friendly inorganic TEs for near-ambient-temperature applications. Metal–organic frameworks (MOFs) share many of the attractive features of organic polymers, including solution processability and low thermal conductivity. A potential advantage of MOFs and MOFs with guest molecules (Guest@MOFs) is their synthetic and structural versatility, which allows both the electronic and geometric structure to be tuned through the choice of metal, ligand, and guest molecules. This could solve the long-standing challenge of findingmore » stable, high-TE-performance n-type organic semiconductors, as well as promote high charge mobility via the long-range crystalline order inherent in these materials. In this paper, we review recent advances in the synthesis of MOF and Guest@MOF TEs and discuss how the Seebeck coefficient, electrical conductivity, and thermal conductivity could be tuned to further optimize TE performance.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talin, Albert Alec; Jones, Reese E.; Hopkins, Patrick E.

Motivated by low cost, low toxicity, mechanical flexibility, and conformability over complex shapes, organic semiconductors are currently being actively investigated as thermoelectric (TE) materials to replace the costly, brittle, and non-eco-friendly inorganic TEs for near-ambient-temperature applications. Metal–organic frameworks (MOFs) share many of the attractive features of organic polymers, including solution processability and low thermal conductivity. A potential advantage of MOFs and MOFs with guest molecules (Guest@MOFs) is their synthetic and structural versatility, which allows both the electronic and geometric structure to be tuned through the choice of metal, ligand, and guest molecules. This could solve the long-standing challenge of findingmore » stable, high-TE-performance n-type organic semiconductors, as well as promote high charge mobility via the long-range crystalline order inherent in these materials. In this paper, we review recent advances in the synthesis of MOF and Guest@MOF TEs and discuss how the Seebeck coefficient, electrical conductivity, and thermal conductivity could be tuned to further optimize TE performance.« less

Positron lifetime beam for defect studies in thin epitaxial semiconductor structures

NASA Astrophysics Data System (ADS)

Laakso, A.; Saarinen, K.; Hautojärvi, P.

2001-12-01

Positron annihilation spectroscopies are methods for direct identification of vacancy-type defects by measuring positron lifetime and Doppler broadening of annihilation radiation and providing information about open volume, concentration and atoms surrounding the defect. Both these techniques are easily applied to bulk samples. Only the Doppler broadening spectroscopy can be employed in thin epitaxial samples by utilizing low-energy positron beams. Here we describe the positron lifetime beam which will provide us with a method to measure lifetime in thin semiconductor layers.

Diode having trenches in a semiconductor region

DOEpatents

Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

2016-03-22

An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

Laser-induced Forward Transfer of Ag Nanopaste.

PubMed

Breckenfeld, Eric; Kim, Heungsoo; Auyeung, Raymond C Y; Piqué, Alberto

2016-03-31

Over the past decade, there has been much development of non-lithographic methods(1-3) for printing metallic inks or other functional materials. Many of these processes such as inkjet(3) and laser-induced forward transfer (LIFT)(4) have become increasingly popular as interest in printable electronics and maskless patterning has grown. These additive manufacturing processes are inexpensive, environmentally friendly, and well suited for rapid prototyping, when compared to more traditional semiconductor processing techniques. While most direct-write processes are confined to two-dimensional structures and cannot handle materials with high viscosity (particularly inkjet), LIFT can transcend both constraints if performed properly. Congruent transfer of three dimensional pixels (called voxels), also referred to as laser decal transfer (LDT)(5-9), has recently been demonstrated with the LIFT technique using highly viscous Ag nanopastes to fabricate freestanding interconnects, complex voxel shapes, and high-aspect-ratio structures. In this paper, we demonstrate a simple yet versatile process for fabricating a variety of micro- and macroscale Ag structures. Structures include simple shapes for patterning electrical contacts, bridging and cantilever structures, high-aspect-ratio structures, and single-shot, large area transfers using a commercial digital micromirror device (DMD) chip.

Laser-induced Forward Transfer of Ag Nanopaste

PubMed Central

Breckenfeld, Eric; Kim, Heungsoo; Auyeung, Raymond C. Y.; Piqué, Alberto

2016-01-01

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of these processes such as inkjet3 and laser-induced forward transfer (LIFT)4 have become increasingly popular as interest in printable electronics and maskless patterning has grown. These additive manufacturing processes are inexpensive, environmentally friendly, and well suited for rapid prototyping, when compared to more traditional semiconductor processing techniques. While most direct-write processes are confined to two-dimensional structures and cannot handle materials with high viscosity (particularly inkjet), LIFT can transcend both constraints if performed properly. Congruent transfer of three dimensional pixels (called voxels), also referred to as laser decal transfer (LDT)5-9, has recently been demonstrated with the LIFT technique using highly viscous Ag nanopastes to fabricate freestanding interconnects, complex voxel shapes, and high-aspect-ratio structures. In this paper, we demonstrate a simple yet versatile process for fabricating a variety of micro- and macroscale Ag structures. Structures include simple shapes for patterning electrical contacts, bridging and cantilever structures, high-aspect-ratio structures, and single-shot, large area transfers using a commercial digital micromirror device (DMD) chip. PMID:27077645

Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Hongliang; Du, Mao-Hua

Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs 2NaInBr 6, Cs 2NaBiCl 6, and Tl 2NaBiCl 6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs 2NaInBr 6 as an example tomore » show that the narrow bands can stabilize self-trapped and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.« less

Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

DOE PAGES

Shi, Hongliang; Du, Mao-Hua

2015-05-12

Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs 2NaInBr 6, Cs 2NaBiCl 6, and Tl 2NaBiCl 6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs 2NaInBr 6 as an example tomore » show that the narrow bands can stabilize self-trapped and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.« less

Magnetosonic solitons in semiconductor plasmas in the presence of quantum tunneling and exchange correlation effects

NASA Astrophysics Data System (ADS)

Hussain, S.; Mahmood, S.

2018-01-01

Low frequency magnetosonic wave excitations are investigated in semiconductor hole-electron plasmas. The quantum mechanical effects such as Fermi pressure, quantum tunneling, and exchange-correlation of holes and electrons in the presence of the magnetic field are considered. The two fluid quantum magnetohydrodynamic model is used to study magnetosonic wave dynamics, while electric and magnetic fields are coupled via Maxwell equations. The dispersion relation of the magnetosonic wave in electron-hole semiconductor plasma propagating in the perpendicular direction of the magnetic field is obtained, and its dispersion effects are discussed. The Korteweg-de Vries equation (KdV) for magnetosonic solitons is derived by employing the reductive perturbation method. For numerical analysis, the plasma parameters are taken from the semiconductors such as GaAs, GaSb, GaN, and InP already existing in the literature. It is found that the phase velocity of the magnetosonic wave is increased with the inclusion of exchange-correlation force in the model. The soliton dip structures of the magnetosonic wave in GaN semiconductor plasma are obtained, which satisfy the quantum plasma conditions for electron and hole fluids. The magnetosonic soliton dip structures move with speed less than the magnetosonic wave phase speed in the lab frame. The effects of exchange-correlation force in the model and variations of magnetic field intensity and electron/hole density on the magnetosonic wave dip structures are also investigated numerically for illustration.

Novel WSi/Au T-shaped gate GaAs metal-semiconductor field-effect-transistor fabrication process for super low-noise microwave monolithic integrated circuit amplifiers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takano, H.; Hosogi, K.; Kato, T.

1995-05-01

A fully ion-implanted self-aligned T-shaped gate Ga As metal-semiconductor field-effect transistor (MESFET) with high frequency and extremely low-noise performance has been successfully fabricated for super low-noise microwave monolithic integrated circuit (MMIC) amplifiers. A subhalf-micrometer gate structure composed of WSi/Ti/Mo/Au is employed to reduce gate resistance effectively. This multilayer gate structure is formed by newly developed dummy SiON self-alignment technology and a photoresist planarization process. At an operating frequency of 12 GHz, a minimum noise figure of 0.87 dB with an associated gain of 10.62 dB has been obtained. Based on the novel FET process, a low-noise single-stage MMIC amplifier withmore » an excellent low-noise figure of 1.2 dB with an associated gain of 8 dB in the 14 GHz band has been realized. This is the lowest noise figure ever reported at this frequency for low-noise MMICs based on ion-implanted self-aligned gate MESFET technology. 14 refs., 9 figs.« less

Leveraging Nanocavity Harmonics for Control of Optical Processes in 2D Semiconductors

DOE PAGES

Akselrod, Gleb M.; Ming, Tian; Argyropoulos, Christos; ...

2015-04-07

Optical cavities with multiple tunable resonances have the potential to provide unique electromagnetic environments at two or more distinct wavelengths–critical for control of optical processes such as nonlinear generation, entangled photon generation, or photoluminescence (PL) enhancement. Here, we show a plasmonic nanocavity based on a nanopatch antenna design that has two tunable resonant modes in the visible spectrum separated by 350 nm and with line widths of ~60 nm. The importance of utilizing two resonances simultaneously is demonstrated by integrating monolayer MoS 2, a two-dimensional semiconductor, into the colloidally synthesized nanocavities. Here, we observe a 2000-fold enhancement in the PLmore » intensity of MoS 2– which has intrinsically low absorption and small quantum yield–at room temperature, enabled by the combination of tailored absorption enhancement at the first harmonic and PL quantum-yield enhancement at the fundamental resonance.« less

Fiber optic coupling of a microlens conditioned, stacked semiconductor laser diode array

DOEpatents

Beach, R.J.; Benett, W.J.; Mills, S.T.

1997-04-01

The output radiation from the two-dimensional aperture of a semiconductor laser diode array is efficiently coupled into an optical fiber. The two-dimensional aperture is formed by stacking individual laser diode bars on top of another in a ``rack and stack`` configuration. Coupling into the fiber is then accomplished using individual microlenses to condition the output radiation of the laser diode bars. A lens that matches the divergence properties and wavefront characteristics of the laser light to the fiber optic is used to focus this conditioned radiation into the fiber. 3 figs.

Optical phonon effect in quasi-one-dimensional semiconductor quantum wires: Band-gap renormalization

NASA Astrophysics Data System (ADS)

Dan, Nguyen Trung; Bechstedt, F.

1996-02-01

We present theoretical studies of dynamical screening in quasi-one-dimensional semiconductor quantum wires including electron-electron and electron-LO-phonon interactions. Within the random-phase approximation we obtain analytical expressions for screened interaction potentials. These expressions can be used to calculate the band-gap renormalization of quantum wires, which depends on the free-carrier density and temperature. We find that the optical phonon interaction effect plays a significant role in band-gap renormalization of quantum wires. The numerical results are compared with some recent experiment measurements as well as available theories.

Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

PubMed Central

Kanbur, Yasin; Irimia-Vladu, Mihai; Głowacki, Eric D.; Voss, Gundula; Baumgartner, Melanie; Schwabegger, Günther; Leonat, Lucia; Ullah, Mujeeb; Sarica, Hizir; Erten-Ela, Sule; Schwödiauer, Reinhard; Sitter, Helmut; Küçükyavuz, Zuhal; Bauer, Siegfried; Sariciftci, Niyazi Serdar

2012-01-01

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C60 as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4 cm2/Vs. Devices with pentacene showed a mobility of 0.16 cm2/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ∼0.3 cm2/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels. PMID:23483783

Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors

PubMed Central

Wang, Jianwei; Zhang, Yong

2016-01-01

When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope.

PubMed

Hieckmann, Ellen; Nacke, Markus; Allardt, Matthias; Bodrov, Yury; Chekhonin, Paul; Skrotzki, Werner; Weber, Jörg

2016-05-28

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

PubMed Central

Hieckmann, Ellen; Nacke, Markus; Allardt, Matthias; Bodrov, Yury; Chekhonin, Paul; Skrotzki, Werner; Weber, Jörg

2016-01-01

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared. PMID:27285177

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime

PubMed Central

Klinger, Markus P.; Fischer, Axel; Kaschura, Felix; Widmer, Johannes; Kheradmand-Boroujeni, Bahman; Ellinger, Frank; Leo, Karl

2017-01-01

In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm−2 and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm2 V−1 s−1, this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed. PMID:28303924

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime.

PubMed

Klinger, Markus P; Fischer, Axel; Kaschura, Felix; Widmer, Johannes; Kheradmand-Boroujeni, Bahman; Ellinger, Frank; Leo, Karl

2017-03-17

In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm -2 and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm 2  V -1  s -1 , this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed.

Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe3

NASA Astrophysics Data System (ADS)

Kong, Tai; Stolze, Karoline; Ni, Danrui; Kushwaha, Satya K.; Cava, Robert J.

2018-01-01

Single crystals of CrSbSe3, a structurally pseudo-one-dimensional ferromagnetic semiconductor, were grown using a high-temperature solution growth technique and were characterized by x-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-dependent resistivity, and optical absorption measurements. A band gap of 0.7 eV was determined from both resistivity and optical measurements. At high temperatures, CrSbSe3 is paramagnetic and isotropic, with a Curie-Weiss temperature of ˜145 K and an effective moment of ˜4.1 μB /Cr. A ferromagnetic transition occurs at Tc=71 K. The a axis, perpendicular to the chains in the structure, is the magnetic easy axis, while the chain axis direction, along b , is the hard axis. Magnetic isotherms measured around Tc do not follow the behavior predicted by simple mean-field critical exponents for a second-order phase transition. A tentative set of critical exponents is estimated based on a modified Arrott plot analysis, giving β ˜0.25 , γ ˜1.38 , and δ ˜6.6 .

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

NASA Astrophysics Data System (ADS)

Sharma, Venus; Srivastava, Sunita

2018-04-01

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Exploration of the Infrared Sensitivity for a ZnSe Electrode of an IR Image Converter

NASA Astrophysics Data System (ADS)

Kurt, H. Hilal

2018-05-01

Significant improvement has been carried out in the field of the II-VI group semiconductor device technology. Semiconductors based on the II-VI group are attractive due to their alternative uses for thermal imaging systems and photonic applications. This study focuses on experimental work on the optical, electrical and structural characterization of an infrared (IR) photodetector zinc selenide (ZnSe). In addition, the IR sensitivity of the ZnSe has primarily been investigated by exploiting the IR responses of the material for various gas pressures, p, and interelectrode distances, d, in the IR converter. The experimental findings include the results of plasma current and plasma discharge emission under various illumination conditions in the IR region. The electron density distributions inside the gas discharge gap have also been simulated in two-dimensional media. Experimentally, the current-voltage, current-time, and discharge light emission plots are produced for a wide experimental parameter range. Consequently, the structural and optical properties have been studied through atomic force microscopy and Fourier-transform infrared spectroscopy techniques to obtain a comprehensive knowledge of the material.

A Comprehensive Review of Semiconductor Ultraviolet Photodetectors: From Thin Film to One-Dimensional Nanostructures

PubMed Central

Sang, Liwen; Liao, Meiyong; Sumiya, Masatomo

2013-01-01

Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga2O3, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications. PMID:23945739

Design and fabrication of one-dimensional and two- dimensional photonic bandgap devices

NASA Astrophysics Data System (ADS)

Lim, Kuo-Yi

1999-10-01

One-dimensional and two-dimensional photonic bandgap devices have been designed and fabricated using III-V compound semiconductors. The one-dimensional photonic bandgap devices consist of monorail and air-bridge waveguide microcavities, while the two-dimensional photonic bandgap devices consist of light-emitting devices with enhanced extraction efficiency. Fabrication techniques such as gas source molecular beam epitaxy, direct-write electron-beam lithography, reactive ion etching and thermal oxidation of AlxGa1- xAs have been employed. The III-V thermal oxide, in particular, is used as an index confinement material, as a sacrificial material for micromechanical fabrication of the air-bridge microcavity, and in the realization of a wide-bandwidth distributed Bragg reflector. The one-dimensional photonic bandgap waveguide microcavities have been designed to operate in the wavelength regimes of 4.5 m m and 1.55 m m. The devices designed to operate in the 1.55 m m wavelength regime have been optically characterized. The transmission spectra exhibit resonances at around 1.55 m m and cavity quality factors (Q's) ranging from 136 to 334. The resonant modal volume is calculated to be about 0.056 m m3. Tunability in the resonance wavelengths has also been demonstrated by changing the size of the defect in the one-dimensional photonic crystal. The two-dimensional photonic bandgap light-emitting device consists of a In0.51Ga0.49P/In0.2Ga0.8As/In 0.51Ga0.49P quantum well emitting at 980nm with a triangular photonic lattice of holes in the top cladding layer of the quantum well. The photonic crystal prohibits the propagation of guided modes in the semiconductor, thus enhancing the extraction of light vertical to the light-emitting device. A wide-bandwidth GaAs/AlxOy distributed Bragg reflector mirror under the quantum well structure further enhances the extraction of light from the devices. The extraction efficiency of the two-dimensional photonic bandgap light-emitting device is expected to be at least 5 times that of a device without the two-dimensional photonic crystal. A photoluminescence measurement setup has been modified to optically characterize these devices. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

FIBRE AND INTEGRATED OPTICS. OPTICAL PROCESSING OF INFORMATION: Feasibility of using waveguide holograms in systems for the transfer of amplitude—phase information along fibre communication lines

NASA Astrophysics Data System (ADS)

Dianov, Evgenii M.; Zubov, Vladimir A.; Putilin, A. N.

1995-02-01

An analysis is made of a variant of a system for spatial—temporal transformation of spatially one-dimensional information for its transfer along a single-mode fibre waveguide. Information is coupled into a fibre by a waveguide hologram. This hologram forms a light-beam structure which matches the fibre-guided mode. A report is given of the use of ion-exchange planar glass waveguides as waveguide holograms. An amorphous chalcogenide semiconductor film or a photoresist was deposited by evaporation on such a planar waveguide. Reconstruction of the waveguide hologram made it possible to achieve a high read rate, up to 1011 pixels per second, when a short radiation pulse was used. Multisectioned injection semiconductor lasers, operating under Q-switching conditions, were used as the radiation sources.

Penta-P2X (X=C, Si) monolayers as wide-bandgap semiconductors: A first principles prediction

NASA Astrophysics Data System (ADS)

Naseri, Mosayeb; Lin, Shiru; Jalilian, Jaafar; Gu, Jinxing; Chen, Zhongfang

2018-06-01

By means of density functional theory computations, we predicted two novel two-dimensional (2D) nanomaterials, namely P2X (X=C, Si) monolayers with pentagonal configurations. Their structures, stabilities, intrinsic electronic, and optical properties as well as the effect of external strain to the electronic properties have been systematically examined. Our computations showed that these P2C and P2Si monolayers have rather high thermodynamic, kinetic, and thermal stabilities, and are indirect semiconductors with wide bandgaps (2.76 eV and 2.69 eV, respectively) which can be tuned by an external strain. These monolayers exhibit high absorptions in the UV region, but behave as almost transparent layers for visible light in the electromagnetic spectrum. Their high stabilities and exceptional electronic and optical properties suggest them as promising candidates for future applications in UV-light shielding and antireflection layers in solar cells.

Field-effect transistor having a superlattice channel and high carrier velocities at high applied fields

DOEpatents

Chaffin, R.J.; Dawson, L.R.; Fritz, I.J.; Osbourn, G.C.; Zipperian, T.E.

1987-06-08

A field effect transistor comprises a semiconductor having a source, a drain, a channel and a gate in operational relationship. The semiconductor is a strained layer superlattice comprising alternating quantum well and barrier layers, the quantum well layers and barrier layers being selected from the group of layer pairs consisting of InGaAs/AlGaAs, InAs/InAlGaAs, and InAs/InAlAsP. The layer thicknesses of the quantum well and barrier layers are sufficiently thin that the alternating layers constitute a superlattice which has a superlattice conduction band energy level structure in k-vector space. The layer thicknesses of the quantum well layers are selected to provide a superlattice L/sub 2D/-valley which has a shape which is substantially more two-dimensional than that of said bulk L-valley. 2 figs.

High-precision, large-domain three-dimensional manipulation of nano-materials for fabrication nanodevices

PubMed Central

2011-01-01

Nanoscaled materials are attractive building blocks for hierarchical assembly of functional nanodevices, which exhibit diverse performances and simultaneous functions. We innovatively fabricated semiconductor nano-probes of tapered ZnS nanowires through melting and solidifying by electro-thermal process; and then, as-prepared nano-probes can manipulate nanomaterials including semiconductor/metal nanowires and nanoparticles through sufficiently electrostatic force to the desired location without structurally and functionally damage. With some advantages of high precision and large domain, we can move and position and interconnect individual nanowires for contracting nanodevices. Interestingly, by the manipulating technique, the nanodevice made of three vertically interconnecting nanowires, i.e., diode, was realized and showed an excellent electrical property. This technique may be useful to fabricate electronic devices based on the nanowires' moving, positioning, and interconnecting and may overcome fundamental limitations of conventional mechanical fabrication. PMID:21794151

Mapping carrier diffusion in single silicon core-shell nanowires with ultrafast optical microscopy.

PubMed

Seo, M A; Yoo, J; Dayeh, S A; Picraux, S T; Taylor, A J; Prasankumar, R P

2012-12-12

Recent success in the fabrication of axial and radial core-shell heterostructures, composed of one or more layers with different properties, on semiconductor nanowires (NWs) has enabled greater control of NW-based device operation for various applications. (1-3) However, further progress toward significant performance enhancements in a given application is hindered by the limited knowledge of carrier dynamics in these structures. In particular, the strong influence of interfaces between different layers in NWs on transport makes it especially important to understand carrier dynamics in these quasi-one-dimensional systems. Here, we use ultrafast optical microscopy (4) to directly examine carrier relaxation and diffusion in single silicon core-only and Si/SiO(2) core-shell NWs with high temporal and spatial resolution in a noncontact manner. This enables us to reveal strong coherent phonon oscillations and experimentally map electron and hole diffusion currents in individual semiconductor NWs for the first time.

Quasi-perpetual discharge behaviour in p-type Ge-air batteries.

PubMed

Ocon, Joey D; Kim, Jin Won; Abrenica, Graniel Harne A; Lee, Jae Kwang; Lee, Jaeyoung

2014-11-07

Metal-air batteries continue to become attractive energy storage and conversion systems due to their high energy and power densities, safer chemistries, and economic viability. Semiconductor-air batteries - a term we first define here as metal-air batteries that use semiconductor anodes such as silicon (Si) and germanium (Ge) - have been introduced in recent years as new high-energy battery chemistries. In this paper, we describe the excellent doping-dependent discharge kinetics of p-type Ge anodes in a semiconductor-air cell employing a gelled KOH electrolyte. Owing to its Fermi level, n-type Ge is expected to have lower redox potential and better electronic conductivity, which could potentially lead to a higher operating voltage and better discharge kinetics. Nonetheless, discharge measurements demonstrated that this prediction is only valid at the low current regime and breaks down at the high current density region. The p-type Ge behaves extremely better at elevated currents, evident from the higher voltage, more power available, and larger practical energy density from a very long discharge time, possibly arising from the high overpotential for surface passivation. A primary semiconductor-air battery, powered by a flat p-type Ge as a multi-electron anode, exhibited an unprecedented full discharge capacity of 1302.5 mA h gGe(-1) (88% anode utilization efficiency), the highest among semiconductor-air cells, notably better than new metal-air cells with three-dimensional and nanostructured anodes, and at least two folds higher than commercial Zn-air and Al-air cells. We therefore suggest that this study be extended to doped-Si anodes, in order to pave the way for a deeper understanding on the discharge phenomena in alkaline metal-air conversion cells with semiconductor anodes for specific niche applications in the future.

Point Defects in Two-Dimensional Layered Semiconductors: Physics and Its Applications

NASA Astrophysics Data System (ADS)

Suh, Joonki

Recent advances in material science and semiconductor processing have been achieved largely based on in-depth understanding, efficient management and advanced application of point defects in host semiconductors, thus finding the relevant techniques such as doping and defect engineering as a traditional scientific and technological solution. Meanwhile, two- dimensional (2D) layered semiconductors currently draw tremendous attentions due to industrial needs and their rich physics at the nanoscale; as we approach the end of critical device dimensions in silicon-based technology, ultra-thin semiconductors have the potential as next- generation channel materials, and new physics also emerges at such reduced dimensions where confinement of electrons, phonons, and other quasi-particles is significant. It is therefore rewarding and interesting to understand and redefine the impact of lattice defects by investigating their interactions with energy/charge carriers of the host matter. Potentially, the established understanding will provide unprecedented opportunities for realizing new functionalities and enhancing the performance of energy harvesting and optoelectronic devices. In this thesis, multiple novel 2D layered semiconductors, such as bismuth and transition- metal chalcogenides, are explored. Following an introduction of conventional effects induced by point defects in semiconductors, the related physics of electronically active amphoteric defects is revisited in greater details. This can elucidate the complication of a two-dimensional electron gas coexisting with the topological states on the surface of bismuth chalcogenides, recently suggested as topological insulators. Therefore, native point defects are still one of the keys to understand and exploit topological insulators. In addition to from a fundamental science point of view, the effects of point defects on the integrated thermal-electrical transport, as well as the entropy-transporting process in thermoelectric materials are thoroughly investigated. Point defects can potentially beat the undesired coupling, often term "thermoelectric Bermuda triangle", among electrical conductivity, thermal conductivity and thermopower. The maximum thermoelectric performance is demonstrated with an intermediate density of defects when they beneficially and multi-functionally act as electron donors, as well as strongly energy-dependent electron and phonon scatterers. Therefore, this is a good example of how fundamental defect physics can be applied for practical devices toward renewable energy technology. Another interesting field of layered nanomaterials is on transition-metal dichalcogenides (TMDs), sensational candidates for 2D semiconductor physics and applications. At the reduced dimensionality of 2D where a far stronger correlation between point defects and charge carriers is expected, it is studied how chalcogen vacancies alter optical properties of monolayer TMDs. A new, sub-bandgap broad emission lines as well as increase in the overall photoluminescence intensity at low temperatures are reported as a result of high quantum efficiency of excitons, i.e., bound electron-hole pairs, localized at defect sites. On electrical transport, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction while typically only one type of doping is stable for a particular TMD. For example, MoS2 is natively n-type, thus the lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2. To address this issue, we demonstrate stable p-type conduction in MoS2 by substitutional Nb doping up to the degenerate level. Proof-of-concept, van der Waals p-n homo-junctions based on vertically stacked MoS2 layers are also fabricated which enable gate-tuneable current rectification. Various electronic devices fabricated are stable in ambient air even without additional treatment such as capping layer protection, thanks to the substitutionality nature of the doping; this is in stark contrast to the existing approach of using molecular doping, which usually suffers from volatility and reactivity with air and/or water molecules.

Method for formation of thin film transistors on plastic substrates

DOEpatents

Carey, P.G.; Smith, P.M.; Sigmon, T.W.; Aceves, R.C.

1998-10-06

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The process relies on techniques for depositing semiconductors, dielectrics, and metals at low temperatures; crystallizing and doping semiconductor layers in the TFT with a pulsed energy source; and creating top-gate self-aligned as well as back-gate TFT structures. The process enables the fabrication of amorphous and polycrystalline channel silicon TFTs at temperatures sufficiently low to prevent damage to plastic substrates. The process has use in large area low cost electronics, such as flat panel displays and portable electronics. 5 figs.

Electroluminescence in SrTiO3:Cr single-crystal nonvolatile memory cells

NASA Astrophysics Data System (ADS)

Alvarado, S. F.; La Mattina, F.; Bednorz, J. G.

2007-10-01

Materials chemistry has emerged as one of the most consistent fabrication tools for the rational delivery of high purity functional nanomaterials, engineered from molecular to microscopic scale at low cost and large scale. An overview of the major achievements and latest advances of a recently developed growth concept and low temperature aqueous synthesis method, for the fabrication of purpose-built large bandgap metal oxide semiconductor materials and oriented nano-arrays is presented. Important insight of direct relevance for semiconductor technology, optoelectronics, photovoltaics and photocatalysis for solar hydrogen generation, are revealed by in-depth investigations of the electronic structure of metal oxide nanostructures with new morphology and architecture, carried out at synchrotron radiation facilities.

Band alignments in Fe/graphene/Si(001) junctions studied by x-ray photoemission spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Breton, J.-C., E-mail: jean-christophe.lebreton@univ-rennes1.fr; Tricot, S.; Delhaye, G.

2016-08-01

The control of tunnel contact resistance is of primary importance for semiconductor-based spintronic devices. This control is hardly achieved with conventional oxide-based tunnel barriers due to deposition-induced interface states. Manipulation of single 2D atomic crystals (such as graphene sheets) weakly interacting with their substrate might represent an alternative and efficient way to design new heterostructures for a variety of different purposes including spin injection into semiconductors. In the present paper, we study by x-ray photoemission spectroscopy the band alignments and interface chemistry of iron–graphene-hydrogenated passivated silicon (001) surfaces for a low and a high n-doping concentration. We find that themore » hydrogen passivation of the Si(001) surface remains efficient even with a graphene sheet on the Si(001) surface. For both doping concentrations, the semiconductor is close to flat-band conditions which indicates that the Fermi level is unpinned on the semiconductor side of the Graphene/Si(001):H interface. When iron is deposited on the graphene/Si(001):H structures, the Schottky barrier height remains mainly unaffected by the metallic overlayer with a very low barrier height for electrons, a sought-after property in semiconductor based spintronic devices. Finally, we demonstrate that the graphene layer intercalated between the metal and semiconductor also serves as a protection against iron-silicide formation even at elevated temperatures preventing from the formation of a Si-based magnetic dead layer.« less

Band alignments in Fe/graphene/Si(001) junctions studied by x-ray photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Le Breton, J.-C.; Tricot, S.; Delhaye, G.; Lépine, B.; Turban, P.; Schieffer, P.

2016-08-01

The control of tunnel contact resistance is of primary importance for semiconductor-based spintronic devices. This control is hardly achieved with conventional oxide-based tunnel barriers due to deposition-induced interface states. Manipulation of single 2D atomic crystals (such as graphene sheets) weakly interacting with their substrate might represent an alternative and efficient way to design new heterostructures for a variety of different purposes including spin injection into semiconductors. In the present paper, we study by x-ray photoemission spectroscopy the band alignments and interface chemistry of iron-graphene-hydrogenated passivated silicon (001) surfaces for a low and a high n-doping concentration. We find that the hydrogen passivation of the Si(001) surface remains efficient even with a graphene sheet on the Si(001) surface. For both doping concentrations, the semiconductor is close to flat-band conditions which indicates that the Fermi level is unpinned on the semiconductor side of the Graphene/Si(001):H interface. When iron is deposited on the graphene/Si(001):H structures, the Schottky barrier height remains mainly unaffected by the metallic overlayer with a very low barrier height for electrons, a sought-after property in semiconductor based spintronic devices. Finally, we demonstrate that the graphene layer intercalated between the metal and semiconductor also serves as a protection against iron-silicide formation even at elevated temperatures preventing from the formation of a Si-based magnetic dead layer.

Substrate induced changes in atomically thin 2-dimensional semiconductors: Fundamentals, engineering, and applications

NASA Astrophysics Data System (ADS)

Sun, Yinghui; Wang, Rongming; Liu, Kai

2017-03-01

Substrate has great influences on materials syntheses, properties, and applications. The influences are particularly crucial for atomically thin 2-dimensional (2D) semiconductors. Their thicknesses are less than 1 nm; however, the lateral sizes can reach up to several inches or more. Therefore, these materials must be placed onto a variety of substrates before subsequent post-processing techniques for final electronic or optoelectronic devices. Recent studies reveal that substrates have been employed as ways to modulate the optical, electrical, mechanical, and chemical properties of 2D semiconductors. In this review, we summarize recent progress upon the effects of substrates on properties of 2D semiconductors, mostly focused on 2D transition metal dichalcogenides, through viewpoints of both fundamental physics and device applications. First, we discuss various effects of substrates, including interface strain, charge transfer, dielectric screening, and optical interference. Second, we show the modulation of 2D semiconductors by substrate engineering, including novel substrates (patterned substrates, 2D-material substrates, etc.) and active substrates (phase transition materials, ferroelectric materials, flexible substrates, etc.). Last, we present prospectives and challenges in this research field. This review provides a comprehensive understanding of the substrate effects, and may inspire new ideas of novel 2D devices based on substrate engineering.

Influence of the Compositional Grading on Concentration of Majority Charge Carriers in Near-Surface Layers of n(p)-HgCdTe Grown by Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.

2018-02-01

The capacitive characteristics of metal-insulator-semiconductor (MIS) structures based on the compositionally graded Hg1-xCdxTe created by molecular beam epitaxy have been experimentally investigated in a wide temperature range (8-77 K). A program has been developed for numerical simulation of ideal capacitance-voltage (C-V) characteristics in the low-frequency and high-frequency approximations. The concentrations of the majority carriers in the near-surface semiconductor layer are determined from the values of the capacitances in the minima of low-frequency C-V curves. For MIS structures based on p-Hg1-xCdxTe, the effect of the presence of the compositionally graded layer on the hole concentration in the near-surface semiconductor layer, determined from capacitive measurements, has not been established. Perhaps this is due to the fact that the concentration of holes in the near-surface layer largely depends on the type of dielectric coating and the regimes of its application. For MIS structures based on n-Hg1-x Cd x Te (x = 0.22-0.23) without a graded-gap layer, the electron concentration determined by the proposed method is close to the average concentration determined by the Hall measurements. The electron concentration in the near-surface semiconductor layer of the compositionally graded n-Hg1-x Cd x Te (x = 0.22-0.23) found from the minimum capacitance value is much higher than the average electron concentration determined by the Hall measurements. The results are qualitatively explained by the creation of additional intrinsic donor-type defects in the near-surface compositionally graded layer of n-Hg1-x Cd x Te.

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Yang, Liu; Wu, Menghao; Yao, Kailun

2018-05-01

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS2 monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958). The ferroelectricity, ferroelasticity and ferromagnetism can be coupled and the magnetization direction may be switched upon ferroelectric/ferroelastic switching, rendering electrical writing + magnetic reading possible. They can be also two-dimensional half-metals or diluted magnetic semiconductors, where p/n channels or even multiferroic tunneling junctions can be designed by variation in doping and incorporated into a monolayer wafer.

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors.

PubMed

Yang, Liu; Wu, Menghao; Yao, Kailun

2018-05-25

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS 2 monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958). The ferroelectricity, ferroelasticity and ferromagnetism can be coupled and the magnetization direction may be switched upon ferroelectric/ferroelastic switching, rendering electrical writing + magnetic reading possible. They can be also two-dimensional half-metals or diluted magnetic semiconductors, where p/n channels or even multiferroic tunneling junctions can be designed by variation in doping and incorporated into a monolayer wafer.

Titanium trisulfide (TiS3): a 2D semiconductor with quasi-1D optical and electronic properties

PubMed Central

Island, Joshua O.; Biele, Robert; Barawi, Mariam; Clamagirand, José M.; Ares, José R.; Sánchez, Carlos; van der Zant, Herre S. J.; Ferrer, Isabel J.; D’Agosta, Roberto; Castellanos-Gomez, Andres

2016-01-01

We present characterizations of few-layer titanium trisulfide (TiS3) flakes which, due to their reduced in-plane structural symmetry, display strong anisotropy in their electrical and optical properties. Exfoliated few-layer flakes show marked anisotropy of their in-plane mobilities reaching ratios as high as 7.6 at low temperatures. Based on the preferential growth axis of TiS3 nanoribbons, we develop a simple method to identify the in-plane crystalline axes of exfoliated few-layer flakes through angle resolved polarization Raman spectroscopy. Optical transmission measurements show that TiS3 flakes display strong linear dichroism with a magnitude (transmission ratios up to 30) much greater than that observed for other anisotropic two-dimensional (2D) materials. Finally, we calculate the absorption and transmittance spectra of TiS3 in the random-phase-approximation (RPA) and find that the calculations are in qualitative agreement with the observed experimental optical transmittance. PMID:26931161

Photocarrier generation from interlayer charge-transfer transitions in WS2-graphene heterostructures

PubMed Central

Yuan, Long; Chung, Ting-Fung; Kuc, Agnieszka; Wan, Yan; Xu, Yang; Chen, Yong P.; Heine, Thomas; Huang, Libai

2018-01-01

Efficient interfacial carrier generation in van der Waals heterostructures is critical for their electronic and optoelectronic applications. We demonstrate broadband photocarrier generation in WS2-graphene heterostructures by imaging interlayer coupling–dependent charge generation using ultrafast transient absorption microscopy. Interlayer charge-transfer (CT) transitions and hot carrier injection from graphene allow carrier generation by excitation as low as 0.8 eV below the WS2 bandgap. The experimentally determined interlayer CT transition energies are consistent with those predicted from the first-principles band structure calculation. CT interactions also lead to additional carrier generation in the visible spectral range in the heterostructures compared to that in the single-layer WS2 alone. The lifetime of the charge-separated states is measured to be ~1 ps. These results suggest that interlayer interactions make graphene–two-dimensional semiconductor heterostructures very attractive for photovoltaic and photodetector applications because of the combined benefits of high carrier mobility and enhanced broadband photocarrier generation. PMID:29423439

Prediction and theoretical characterization of p-type organic semiconductor crystals for field-effect transistor applications.

PubMed

Atahan-Evrenk, Sule; Aspuru-Guzik, Alán

2014-01-01

The theoretical prediction and characterization of the solid-state structure of organic semiconductors has tremendous potential for the discovery of new high performance materials. To date, the theoretical analysis mostly relied on the availability of crystal structures obtained through X-ray diffraction. However, the theoretical prediction of the crystal structures of organic semiconductor molecules remains a challenge. This review highlights some of the recent advances in the determination of structure-property relationships of the known organic semiconductor single-crystals and summarizes a few available studies on the prediction of the crystal structures of p-type organic semiconductors for transistor applications.

Reducing leakage current in semiconductor devices

DOEpatents

Lu, Bin; Matioli, Elison de Nazareth; Palacios, Tomas Apostol

2018-03-06

A semiconductor device includes a first region having a first semiconductor material and a second region having a second semiconductor material. The second region is formed over the first region. The semiconductor device also includes a current blocking structure formed in the first region between first and second terminals of the semiconductor device. The current blocking structure is configured to reduce current flow in the first region between the first and second terminals.

Rapid Three-Dimensional Printing in Water Using Semiconductor-Metal Hybrid Nanoparticles as Photoinitiators.

PubMed

Pawar, Amol Ashok; Halivni, Shira; Waiskopf, Nir; Ben-Shahar, Yuval; Soreni-Harari, Michal; Bergbreiter, Sarah; Banin, Uri; Magdassi, Shlomo

2017-07-12

Additive manufacturing processes enable fabrication of complex and functional three-dimensional (3D) objects ranging from engine parts to artificial organs. Photopolymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes photoinitiators that break into radicals upon light absorption. We report on a new family of photoinitiators for 3D printing based on hybrid semiconductor-metal nanoparticles. Unlike conventional photoinitiators that are consumed upon irradiation, these particles form radicals through a photocatalytic process. Light absorption by the semiconductor nanorod is followed by charge separation and electron transfer to the metal tip, enabling redox reactions to form radicals in aerobic conditions. In particular, we demonstrate their use in 3D printing in water, where they simultaneously form hydroxyl radicals for the polymerization and consume dissolved oxygen that is a known inhibitor. We also demonstrate their potential for two-photon polymerization due to their giant two-photon absorption cross section.

Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

PubMed Central

Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D

2017-01-01

An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120±32 nm, which may be improved with further optimization of the nanopillar dimensions. PMID:28530219

Characteristics of Superjunction Lateral-Double-Diffusion Metal Oxide Semiconductor Field Effect Transistor and Degradation after Electrical Stress

NASA Astrophysics Data System (ADS)

Lin, Jyh‑Ling; Lin, Ming‑Jang; Lin, Li‑Jheng

2006-04-01

The superjunction lateral double diffusion metal oxide semiconductor field effect has recently received considerable attention. Introducing heavily doped p-type strips to the n-type drift region increases the horizontal depletion capability. Consequently, the doping concentration of the drift region is higher and the conduction resistance is lower than those of conventional lateral-double-diffusion metal oxide semiconductor field effect transistors (LDMOSFETs). These characteristics may increase breakdown voltage (\\mathit{BV}) and reduce specific on-resistance (Ron,sp). In this study, we focus on the electrical characteristics of conventional LDMOSFETs on silicon bulk, silicon-on-insulator (SOI) LDMOSFETs and superjunction LDMOSFETs after bias stress. Additionally, the \\mathit{BV} and Ron,sp of superjunction LDMOSFETs with different N/P drift region widths and different dosages are discussed. Simulation tools, including two-dimensional (2-D) TSPREM-4/MEDICI and three-dimensional (3-D) DAVINCI, were employed to determine the device characteristics.

Complexes of dipolar excitons in layered quasi-two-dimensional nanostructures

NASA Astrophysics Data System (ADS)

Bondarev, Igor V.; Vladimirova, Maria R.

2018-04-01

We discuss neutral and charged complexes (biexcitons and trions) formed by indirect excitons in layered quasi-two-dimensional semiconductor heterostructures. Indirect excitons—long-lived neutral Coulomb-bound pairs of electrons and holes of different layers—have been known for semiconductor coupled quantum wells and have recently been reported for van der Waals heterostructures such as double bilayer graphene and transition-metal dichalcogenides. Using the configuration space approach, we derive the analytical expressions for the trion and biexciton binding energies as a function of interlayer distance. The method captures essential kinematics of complex formation to reveal significant binding energies, up to a few tens of meV for typical interlayer distances ˜3 -5 Å , with the trion binding energy always being greater than that of the biexciton. Our results can contribute to the understanding of more complex many-body phenomena such as exciton Bose-Einstein condensation and Wigner-like electron-hole crystallization in layered semiconductor heterostructures.

Band structure engineering of semiconductors for enhanced photoelectrochemical water splitting: The case of TiO2

NASA Astrophysics Data System (ADS)

Yin, Wan-Jian; Tang, Houwen; Wei, Su-Huai; Al-Jassim, Mowafak M.; Turner, John; Yan, Yanfa

2010-07-01

Here, we propose general strategies for the rational design of semiconductors to simultaneously meet all of the requirements for a high-efficiency, solar-driven photoelectrochemical (PEC) water-splitting device. As a case study, we apply our strategies for engineering the popular semiconductor, anatase TiO2 . Previous attempts to modify known semiconductors such as TiO2 have often focused on a particular individual criterion such as band gap, neglecting the possible detrimental consequence to other important criteria. Density-functional theory calculations reveal that with appropriate donor-acceptor coincorporation alloys with anatase TiO2 hold great potential to satisfy all of the criteria for a viable PEC device. We predict that (Mo, 2N) and (W, 2N) are the best donor-acceptor combinations in the low-alloy concentration regime whereas (Nb, N) and (Ta, N) are the best choice of donor-acceptor pairs in the high-alloy concentration regime.

Rational In Silico Design of an Organic Semiconductor with Improved Electron Mobility.

PubMed

Friederich, Pascal; Gómez, Verónica; Sprau, Christian; Meded, Velimir; Strunk, Timo; Jenne, Michael; Magri, Andrea; Symalla, Franz; Colsmann, Alexander; Ruben, Mario; Wenzel, Wolfgang

2017-11-01

Organic semiconductors find a wide range of applications, such as in organic light emitting diodes, organic solar cells, and organic field effect transistors. One of their most striking disadvantages in comparison to crystalline inorganic semiconductors is their low charge-carrier mobility, which manifests itself in major device constraints such as limited photoactive layer thicknesses. Trial-and-error attempts to increase charge-carrier mobility are impeded by the complex interplay of the molecular and electronic structure of the material with its morphology. Here, the viability of a multiscale simulation approach to rationally design materials with improved electron mobility is demonstrated. Starting from one of the most widely used electron conducting materials (Alq 3 ), novel organic semiconductors with tailored electronic properties are designed for which an improvement of the electron mobility by three orders of magnitude is predicted and experimentally confirmed. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

New Material Transistor with Record-High Field-Effect Mobility among Wide-Band-Gap Semiconductors.

PubMed

Shih, Cheng Wei; Chin, Albert

2016-08-03

At an ultrathin 5 nm, we report a new high-mobility tin oxide (SnO2) metal-oxide-semiconductor field-effect transistor (MOSFET) exhibiting extremely high field-effect mobility values of 279 and 255 cm(2)/V-s at 145 and 205 °C, respectively. These values are the highest reported mobility values among all wide-band-gap semiconductors of GaN, SiC, and metal-oxide MOSFETs, and they also exceed those of silicon devices at the aforementioned elevated temperatures. For the first time among existing semiconductor transistors, a new device physical phenomenon of a higher mobility value was measured at 45-205 °C than at 25 °C, which is due to the lower optical phonon scattering by the large SnO2 phonon energy. Moreover, the high on-current/off-current of 4 × 10(6) and the positive threshold voltage of 0.14 V at 25 °C are significantly better than those of a graphene transistor. This wide-band-gap SnO2 MOSFET exhibits high mobility in a 25-205 °C temperature range, a wide operating voltage of 1.5-20 V, and the ability to form on an amorphous substrate, rendering it an ideal candidate for multifunctional low-power integrated circuit (IC), display, and brain-mimicking three-dimensional IC applications.

Fabrication of Smooth Patterned Structures of Refractory Metals, Semiconductors, and Oxides via Template Stripping

PubMed Central

2013-01-01

The template-stripping method can yield smooth patterned films without surface contamination. However, the process is typically limited to coinage metals such as silver and gold because other materials cannot be readily stripped from silicon templates due to strong adhesion. Herein, we report a more general template-stripping method that is applicable to a larger variety of materials, including refractory metals, semiconductors, and oxides. To address the adhesion issue, we introduce a thin gold layer between the template and the deposited materials. After peeling off the combined film from the template, the gold layer can be selectively removed via wet etching to reveal a smooth patterned structure of the desired material. Further, we demonstrate template-stripped multilayer structures that have potential applications for photovoltaics and solar absorbers. An entire patterned device, which can include a transparent conductor, semiconductor absorber, and back contact, can be fabricated. Since our approach can also produce many copies of the patterned structure with high fidelity by reusing the template, a low-cost and high-throughput process in micro- and nanofabrication is provided that is useful for electronics, plasmonics, and nanophotonics. PMID:24001174

Photoprecursor Approach Enables Preparation of Well-Performing Bulk-Heterojunction Layers Comprising a Highly Aggregating Molecular Semiconductor.

PubMed

Suzuki, Mitsuharu; Yamaguchi, Yuji; Takahashi, Kohei; Takahira, Katsuya; Koganezawa, Tomoyuki; Masuo, Sadahiro; Nakayama, Ken-ichi; Yamada, Hiroko

2016-04-06

Active-layer morphology critically affects the performance of organic photovoltaic cells, and thus its optimization is a key toward the achievement of high-efficiency devices. However, the optimization of active-layer morphology is sometimes challenging because of the intrinsic properties of materials such as strong self-aggregating nature or low miscibility. This study postulates that the "photoprecursor approach" can serve as an effective means to prepare well-performing bulk-heterojunction (BHJ) layers containing highly aggregating molecular semiconductors. In the photoprecursor approach, a photoreactive precursor compound is solution-deposited and then converted in situ to a semiconducting material. This study employs 2,6-di(2-thienyl)anthracene (DTA) and [6,6]-phenyl-C71-butyric acid methyl ester as p- and n-type materials, respectively, in which DTA is generated by the photoprecursor approach from the corresponding α-diketone-type derivative DTADK. When only chloroform is used as a cast solvent, the photovoltaic performance of the resulting BHJ films is severely limited because of unfavorable film morphology. The addition of a high-boiling-point cosolvent, o-dichlorobenzene (o-DCB), to the cast solution leads to significant improvement such that the resulting active layers afford up to approximately 5 times higher power conversion efficiencies. The film structure is investigated by two-dimensional grazing-incident wide-angle X-ray diffraction, atomic force microscopy, and fluorescence microspectroscopy to demonstrate that the use of o-DCB leads to improvement in film crystallinity and increase in charge-carrier generation efficiency. The change in film structure is assumed to originate from dynamic molecular motion enabled by the existence of solvent during the in situ photoreaction. The unique features of the photoprecursor approach will be beneficial in extending the material and processing scopes for the development of organic thin-film devices.

Chiral tunneling in gated inversion symmetric Weyl semimetal.

PubMed

Bai, Chunxu; Yang, Yanling; Chang, Kai

2016-02-18

Based on the chirality-resolved transfer-matrix method, we evaluate the chiral transport tunneling through Weyl semimetal multi-barrier structures created by periodic gates. It is shown that, in sharp contrast to the cases of three dimensional normal semimetals, the tunneling coefficient as a function of incident angle shows a strong anisotropic behavior. Importantly, the tunneling coefficients display an interesting periodic oscillation as a function of the crystallographic angle of the structures. With the increasement of the barriers, the tunneling current shows a Fabry-Perot type interferences. For superlattice structures, the fancy miniband effect has been revealed. Our results show that the angular dependence of the first bandgap can be reduced into a Lorentz formula. The disorder suppresses the oscillation of the tunneling conductance, but would not affect its average amplitude. This is in sharp contrast to that in multi-barrier conventional semiconductor structures. Moreover, numerical results for the dependence of the angularly averaged conductance on the incident energy and the structure parameters are presented and contrasted with those in two dimensional relativistic materials. Our work suggests that the gated Weyl semimetal opens a possible new route to access to new type nanoelectronic device.

Chiral tunneling in gated inversion symmetric Weyl semimetal

PubMed Central

Bai, Chunxu; Yang, Yanling; Chang, Kai

2016-01-01

Based on the chirality-resolved transfer-matrix method, we evaluate the chiral transport tunneling through Weyl semimetal multi-barrier structures created by periodic gates. It is shown that, in sharp contrast to the cases of three dimensional normal semimetals, the tunneling coefficient as a function of incident angle shows a strong anisotropic behavior. Importantly, the tunneling coefficients display an interesting periodic oscillation as a function of the crystallographic angle of the structures. With the increasement of the barriers, the tunneling current shows a Fabry-Perot type interferences. For superlattice structures, the fancy miniband effect has been revealed. Our results show that the angular dependence of the first bandgap can be reduced into a Lorentz formula. The disorder suppresses the oscillation of the tunneling conductance, but would not affect its average amplitude. This is in sharp contrast to that in multi-barrier conventional semiconductor structures. Moreover, numerical results for the dependence of the angularly averaged conductance on the incident energy and the structure parameters are presented and contrasted with those in two dimensional relativistic materials. Our work suggests that the gated Weyl semimetal opens a possible new route to access to new type nanoelectronic device. PMID:26888491

Low-Dimensional Organic-Inorganic Halide Perovskite: Structure, Properties, and Applications.

PubMed

Misra, Ravi K; Cohen, Bat-El; Iagher, Lior; Etgar, Lioz

2017-10-09

Three-dimensional (3 D) perovskite has attracted a lot of attention owing to its success in photovoltaic (PV) solar cells. However, one of its major crucial issues lies in its stability, which has limited its commercialization. An important property of organic-inorganic perovskite is the possibility of forming a layered material by using long organic cations that do not fit into the octahedral cage. These long organic cations act as a "barrier" that "caps" 3 D perovskite to form the layered material. Controlling the number of perovskite layers could provide a confined structure with chemical and physical properties that are different from those of 3 D perovskite. This opens up a whole new batch of interesting materials with huge potential for optoelectronic applications. This Minireview presents the synthesis, properties, and structural orientation of low-dimensional perovskite. It also discusses the progress of low-dimensional perovskite in PV solar cells, which, to date, have performance comparable to that of 3 D perovskite but with enhanced stability. Finally, the use of low-dimensional perovskite in light-emitting diodes (LEDs) and photodetectors is discussed. The low-dimensional perovskites are promising candidates for LED devices, mainly because of their high radiative recombination as a result of the confined low-dimensional quantum well. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-Dimensional Harmonic Model for Biomolecules

PubMed Central

Krizan, John E.

1973-01-01

Following in spirit a paper by Rosen, we propose a one-dimensional harmonic model for biomolecules. Energy bands with gaps of the order of semi-conductor gaps are found. The method is discussed for general symmetric and periodic potential functions. PMID:4709518

Single-layer group IV-V and group V-IV-III-VI semiconductors: Structural stability, electronic structures, optical properties, and photocatalysis

NASA Astrophysics Data System (ADS)

Lin, Jia-He; Zhang, Hong; Cheng, Xin-Lu; Miyamoto, Yoshiyuki

2017-07-01

Recently, single-layer group III monochalcogenides have attracted both theoretical and experimental interest at their potential applications in photonic devices, electronic devices, and solar energy conversion. Excited by this, we theoretically design two kinds of highly stable single-layer group IV-V (IV =Si ,Ge , and Sn; V =N and P) and group V-IV-III-VI (IV =Si ,Ge , and Sn; V =N and P; III =Al ,Ga , and In; VI =O and S) compounds with the same structures with single-layer group III monochalcogenides via first-principles simulations. By using accurate hybrid functional and quasiparticle methods, we show the single-layer group IV-V and group V-IV-III-VI are indirect bandgap semiconductors with their bandgaps and band edge positions conforming to the criteria of photocatalysts for water splitting. By applying a biaxial strain on single-layer group IV-V, single-layer group IV nitrides show a potential on mechanical sensors due to their bandgaps showing an almost linear response for strain. Furthermore, our calculations show that both single-layer group IV-V and group V-IV-III-VI have absorption from the visible light region to far-ultraviolet region, especially for single-layer SiN-AlO and SnN-InO, which have strong absorption in the visible light region, resulting in excellent potential for solar energy conversion and visible light photocatalytic water splitting. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting.

An existence criterion for low-dimensional materials

NASA Astrophysics Data System (ADS)

Chen, Jiapeng; Wang, Biao; Hu, Yangfan

2017-10-01

The discovery of graphene and other two-dimensional (2-D) materials has stimulated a general interest in low-dimensional (low-D) materials. Whereas long time ago, Peierls (1935) and Landau's (1937) theoretical work demonstrated that any one- and two-dimensional materials could not exist in any finite temperature environment. Then, two basic issues became a central concern for many researchers: How can stable low-D materials exist? What kind of low-D materials are stable? Here, we establish an energy stability criterion for low-D materials, which seeks to provide a clear answer to these questions. For a certain kind of element, the stability of its specific low-D structure is determined by several derivatives of its interatomic potential. This atomistic-based approach is then applied to study any straight/planar, low-D, equal-bond-length elemental materials. We found that 1-D monatomic chains, 2-D honeycomb lattices, square lattices, and triangular lattices are the only four permissible structures, and the stability of these structures can only be understood by assuming multi-body interatomic potentials. Using this approach, the stable existence of graphene, silicene and germanene can be explained.

Fundamentals, progress, and future directions of nitride-based semiconductors and their composites in two-dimensional limit: A first-principles perspective to recent synthesis

NASA Astrophysics Data System (ADS)

Kecik, D.; Onen, A.; Konuk, M.; Gürbüz, E.; Ersan, F.; Cahangirov, S.; Aktürk, E.; Durgun, E.; Ciraci, S.

2018-03-01

Potential applications of bulk GaN and AlN crystals have made possible single and multilayer allotropes of these III-V compounds to be a focus of interest recently. As of 2005, the theoretical studies have predicted that GaN and AlN can form two-dimensional (2D) stable, single-layer (SL) structures being wide band gap semiconductors and showing electronic and optical properties different from those of their bulk parents. Research on these 2D structures have gained importance with recent experimental studies achieving the growth of ultrathin 2D GaN and AlN on substrates. It is expected that these two materials will open an active field of research like graphene, silicene, and transition metal dichalcogenides. This topical review aims at the evaluation of previous experimental and theoretical works until 2018 in order to provide input for further research attempts in this field. To this end, starting from three-dimensional (3D) GaN and AlN crystals, we review 2D SL and multilayer (ML) structures, which were predicted to be stable in free-standing states. These are planar hexagonal (or honeycomb), tetragonal, and square-octagon structures. First, we discuss earlier results on dynamical and thermal stability of these SL structures, as well as the predicted mechanical properties. Next, their electronic and optical properties with and without the effect of strain are reviewed and compared with those of the 3D parent crystals. The formation of multilayers, hence prediction of new periodic layered structures and also tuning their physical properties with the number of layers are other critical subjects that have been actively studied and discussed here. In particular, an extensive analysis pertaining to the nature of perpendicular interlayer bonds causing planar GaN and AlN to buckle is presented. In view of the fact that SL GaN and AlN can be fabricated only on a substrate, the question of how the properties of free-standing, SL structures are affected if they are grown on a substrate is addressed. We also examine recent works treating the composite structures of GaN and AlN joined commensurately along their zigzag and armchair edges and forming heterostructures, δ-doping, single, and multiple quantum wells, as well as core/shell structures. Finally, outlooks and possible new research directions are briefly discussed.

Unraveling the Chemical Nature of the 3D "Hollow" Hybrid Halide Perovskites.

PubMed

Spanopoulos, Ioannis; Ke, Weijun; Stoumpos, Constantinos C; Schueller, Emily C; Kontsevoi, Oleg Y; Seshadri, Ram; Kanatzidis, Mercouri G

2018-05-02

The newly introduced class of 3D halide perovskites, termed "hollow" perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) AMX 3 perovskites ( A = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations ( en) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, 1 H NMR, TGA, SEM/EDX), we have assigned the general formula (A) 1- x ( en) x (M) 1-0.7 x (X) 3-0.4 x to the hollow perovskites. The incorporation of en in the 3D perovskite structure leads to massive M and X vacancies in the 3D [ MX 3 ] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive M and X vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI 3 and FASnI 3 . The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells.

Steep-slope hysteresis-free negative capacitance MoS2 transistors

NASA Astrophysics Data System (ADS)

Si, Mengwei; Su, Chun-Jung; Jiang, Chunsheng; Conrad, Nathan J.; Zhou, Hong; Maize, Kerry D.; Qiu, Gang; Wu, Chien-Ting; Shakouri, Ali; Alam, Muhammad A.; Ye, Peide D.

2018-01-01

The so-called Boltzmann tyranny defines the fundamental thermionic limit of the subthreshold slope of a metal-oxide-semiconductor field-effect transistor (MOSFET) at 60 mV dec-1 at room temperature and therefore precludes lowering of the supply voltage and overall power consumption1,2. Adding a ferroelectric negative capacitor to the gate stack of a MOSFET may offer a promising solution to bypassing this fundamental barrier3. Meanwhile, two-dimensional semiconductors such as atomically thin transition-metal dichalcogenides, due to their low dielectric constant and ease of integration into a junctionless transistor topology, offer enhanced electrostatic control of the channel4-12. Here, we combine these two advantages and demonstrate a molybdenum disulfide (MoS2) two-dimensional steep-slope transistor with a ferroelectric hafnium zirconium oxide layer in the gate dielectric stack. This device exhibits excellent performance in both on and off states, with a maximum drain current of 510 μA μm-1 and a sub-thermionic subthreshold slope, and is essentially hysteresis-free. Negative differential resistance was observed at room temperature in the MoS2 negative-capacitance FETs as the result of negative capacitance due to the negative drain-induced barrier lowering. A high on-current-induced self-heating effect was also observed and studied.

Accelerating Gas Adsorption on 3D Percolating Carbon Nanotubes.

PubMed

Li, Hui; Wen, Chenyu; Zhang, Youwei; Wu, Dongping; Zhang, Shi-Li; Qiu, Zhi-Jun

2016-02-18

In the field of electronic gas sensing, low-dimensional semiconductors such as single-walled carbon nanotubes (SWCNTs) can offer high detection sensitivity owing to their unprecedentedly large surface-to-volume ratio. The sensitivity and responsivity can further improve by increasing their areal density. Here, an accelerated gas adsorption is demonstrated by exploiting volumetric effects via dispersion of SWCNTs into a percolating three-dimensional (3D) network in a semiconducting polymer. The resultant semiconducting composite film is evaluated as a sensing membrane in field effect transistor (FET) sensors. In order to attain reproducible characteristics of the FET sensors, a pulsed-gate-bias measurement technique is adopted to eliminate current hysteresis and drift of sensing baseline. The rate of gas adsorption follows the Langmuir-type isotherm as a function of gas concentration and scales with film thickness. This rate is up to 5 times higher in the composite than only with an SWCNT network in the transistor channel, which in turn results in a 7-fold shorter time constant of adsorption with the composite. The description of gas adsorption developed in the present work is generic for all semiconductors and the demonstrated composite with 3D percolating SWCNTs dispersed in functional polymer represents a promising new type of material for advanced gas sensors.

Differential-Mode Biosensor Using Dual Extended-Gate Metal-Oxide-Semiconductor Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Choi, Jinhyeon; Lee, Hee Ho; Ahn, Jungil; Seo, Sang-Ho; Shin, Jang-Kyoo

2012-06-01

In this paper, we present a differential-mode biosensor using dual extended-gate metal-oxide-semiconductor field-effect transistors (MOSFETs), which possesses the advantages of both the extended-gate structure and the differential-mode operation. The extended-gate MOSFET was fabricated using a 0.6 µm standard complementary metal oxide semiconductor (CMOS) process. The Au extended gate is the sensing gate on which biomolecules are immobilized, while the Pt extended gate is the dummy gate for use in the differential-mode detection circuit. The differential-mode operation offers many advantages such as insensitivity to the variation of temperature and light, as well as low noise. The outputs were measured using a semiconductor parameter analyzer in a phosphate buffered saline (PBS; pH 7.4) solution. A standard Ag/AgCl reference electrode was used to apply the gate bias. We measured the variation of output voltage with time, temperature, and light intensity. The bindings of self-assembled monolayer (SAM), streptavidin, and biotin caused a variation in the output voltage of the differential-mode detection circuit and this was confirmed by surface plasmon resonance (SPR) experiment. Biotin molecules could be detected up to a concentration of as low as 0.001 µg/ml.

Correlated electron-hole mechanism for molecular doping in organic semiconductors

NASA Astrophysics Data System (ADS)

Li, Jing; D'Avino, Gabriele; Pershin, Anton; Jacquemin, Denis; Duchemin, Ivan; Beljonne, David; Blase, Xavier

2017-07-01

The electronic and optical properties of the paradigmatic F4TCNQ-doped pentacene in the low-doping limit are investigated by a combination of state-of-the-art many-body ab initio methods accounting for environmental screening effects, and a carefully parametrized model Hamiltonian. We demonstrate that while the acceptor level lies very deep in the gap, the inclusion of electron-hole interactions strongly stabilizes dopant-semiconductor charge transfer states and, together with spin statistics and structural relaxation effects, rationalize the possibility for room-temperature dopant ionization. Our findings reconcile available experimental data, shedding light on the partial vs. full charge transfer scenario discussed in the literature, and question the relevance of the standard classification in shallow or deep impurity levels prevailing for inorganic semiconductors.

Characterizing the Three-Dimensional Structure of Block Copolymers via Sequential Infiltration Synthesis and Scanning Transmission Electron Tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Segal-Peretz, Tamar; Winterstein, Jonathan; Doxastakis, Manolis

Understanding and controlling the three-dimensional structure of block copolymer (BCP) thin films is critical for utilizing these materials for sub-20 nm nanopatterning in semiconductor devices, as well as in membranes and solar cell applications. Combining an atomic layer deposition (ALD) based technique for enhancing the contrast of BCPs in transmission electron microscopy (TEM) together with scanning TEM (STEM) tomography reveals and characterizes the three-dimensional structures of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) thin films with great clarity. Sequential infiltration synthesis (SIS), a block-selective technique for growing inorganic materials in BCPs films in ALD, and an emerging tool for enhancing the etch contrast ofmore » BCPs, was harnessed to significantly enhance the high-angle scattering from the polar domains of BCP films in the TEM. The power of combining SIS and STEM tomography for three dimensional (3D) characterization of BCPs films was demonstrated with the following cases: self-assembled cylindrical, lamellar, and spherical PS-PMMA thin films. In all cases, STEM tomography has revealed 3D structures that were hidden underneath the surface, including: 1) the 3D structure of defects in cylindrical and lamellar phases, 2) non-perpendicular 3D surface of grain boundaries in the cylindrical phase, and 3) the 3D arrangement of spheres in body centered cubic (BCC) and hexagonal closed pack (HCP) morphologies in the spherical phase. The 3D data of the spherical morphologies was compared to coarse-grained simulations and assisted in validating the simulations’ parameters. STEM tomography of SIS-treated BCP films enables the characterization of the exact structure used for pattern transfer, and can lead to better understating of the physics which is utilized in BCP lithography.« less

Metrology of semiconductor structures using novel Fabry Perot fringe stretching system

NASA Astrophysics Data System (ADS)

Walecki, Wojtek J.; Pravdivtsev, Alexander

2017-08-01

We describe patent pending fiber optic apparatus for measurements of thicknesses and distance employing low resolution spectrometer and etalon. The application of an additional known reference etalon "stretches fringes" and allows us to use Fabry Perot interference to investigate thick samples and large distances which would not be possible when using the low resolution spectrometer alone.

Electrical transport properties in indium tin oxide films prepared by electron-beam evaporation

NASA Astrophysics Data System (ADS)

Liu, X. D.; Jiang, E. Y.; Zhang, D. X.

2008-10-01

Amorphous and polycrystalline indium tin oxide films have been prepared by electron-beam evaporation method. The amorphous films exhibit semiconductor behavior, while metallic conductivity is observed in the polycrystalline samples. The magnetoconductivities of the polycrystalline films are positive at low temperatures and can be well described by the theory of three-dimensional weak-localization effect. In addition, the electron phase-breaking rate is proportional to T3/2. Comparing the experimental results with theory, we find that the electron-electron scattering is the dominant destroyer of the constructive interference in the films. In addition, the Coulomb interaction is the main contribution to the nontrivial corrections for the electrical conductivity at low temperatures.

Atomically resolved scanning force studies of vicinal Si(111)

NASA Astrophysics Data System (ADS)

Pérez León, Carmen; Drees, Holger; Wippermann, Stefan Martin; Marz, Michael; Hoffmann-Vogel, Regina

2017-06-01

Well-ordered stepped semiconductor surfaces attract intense attention owing to the regular arrangements of their atomic steps that makes them perfect templates for the growth of one-dimensional systems, e.g., nanowires. Here, we report on the atomic structure of the vicinal Si (111 ) surface with 10∘ miscut investigated by a joint frequency-modulation scanning force microscopy (FM-SFM) and ab initio approach. This popular stepped surface contains 7 ×7 -reconstructed terraces oriented along the Si (111 ) direction, separated by a stepped region. Recently, the atomic structure of this triple step based on scanning tunneling microscopy (STM) images has been subject of debate. Unlike STM, SFM atomic resolution capability arises from chemical bonding of the tip apex with the surface atoms. Thus, for surfaces with a corrugated density of states such as semiconductors, SFM provides complementary information to STM and partially removes the dependency of the topography on the electronic structure. Our FM-SFM images with unprecedented spatial resolution on steps coincide with the model based on a (7 7 10 ) orientation of the surface and reveal structural details of this surface. Two different FM-SFM contrasts together with density functional theory calculations explain the presence of defects, buckling, and filling asymmetries on the surface. Our results evidence the important role of charge transfers between adatoms, restatoms, and dimers in the stabilisation of the structure of the vicinal surface.

Monolithically Integrated High-β Nanowire Lasers on Silicon.

PubMed

Mayer, B; Janker, L; Loitsch, B; Treu, J; Kostenbader, T; Lichtmannecker, S; Reichert, T; Morkötter, S; Kaniber, M; Abstreiter, G; Gies, C; Koblmüller, G; Finley, J J

2016-01-13

Reliable technologies for the monolithic integration of lasers onto silicon represent the holy grail for chip-level optical interconnects. In this context, nanowires (NWs) fabricated using III-V semiconductors are of strong interest since they can be grown site-selectively on silicon using conventional epitaxial approaches. Their unique one-dimensional structure and high refractive index naturally facilitate low loss optical waveguiding and optical recirculation in the active NW-core region. However, lasing from NWs on silicon has not been achieved to date, due to the poor modal reflectivity at the NW-silicon interface. We demonstrate how, by inserting a tailored dielectric interlayer at the NW-Si interface, low-threshold single mode lasing can be achieved in vertical-cavity GaAs-AlGaAs core-shell NW lasers on silicon as measured at low temperature. By exploring the output characteristics along a detection direction parallel to the NW-axis, we measure very high spontaneous emission factors comparable to nanocavity lasers (β = 0.2) and achieve ultralow threshold pump energies ≤11 pJ/pulse. Analysis of the input-output characteristics of the NW lasers and the power dependence of the lasing emission line width demonstrate the potential for high pulsation rates ≥250 GHz. Such highly efficient nanolasers grown monolithically on silicon are highly promising for the realization of chip-level optical interconnects.