Image Quality Characteristics of Handheld Display Devices for Medical Imaging

PubMed Central

Yamazaki, Asumi; Liu, Peter; Cheng, Wei-Chung; Badano, Aldo

2013-01-01

Handheld devices such as mobile phones and tablet computers have become widespread with thousands of available software applications. Recently, handhelds are being proposed as part of medical imaging solutions, especially in emergency medicine, where immediate consultation is required. However, handheld devices differ significantly from medical workstation displays in terms of display characteristics. Moreover, the characteristics vary significantly among device types. We investigate the image quality characteristics of various handheld devices with respect to luminance response, spatial resolution, spatial noise, and reflectance. We show that the luminance characteristics of the handheld displays are different from those of workstation displays complying with grayscale standard target response suggesting that luminance calibration might be needed. Our results also demonstrate that the spatial characteristics of handhelds can surpass those of medical workstation displays particularly for recent generation devices. While a 5 mega-pixel monochrome workstation display has horizontal and vertical modulation transfer factors of 0.52 and 0.47 at the Nyquist frequency, the handheld displays released after 2011 can have values higher than 0.63 at the respective Nyquist frequencies. The noise power spectra for workstation displays are higher than 1.2×10−5 mm2 at 1 mm−1, while handheld displays have values lower than 3.7×10−6 mm2. Reflectance measurements on some of the handheld displays are consistent with measurements for workstation displays with, in some cases, low specular and diffuse reflectance coefficients. The variability of the characterization results among devices due to the different technological features indicates that image quality varies greatly among handheld display devices. PMID:24236113

Device Performance and Reliability Improvements of AlGaBN/GaN/Si MOSFET

DTIC Science & Technology

2016-02-04

Metal insulator semiconductor AlGaN /GaN high electron mobility transistors (MISHEMTs) are promising for power device applications due to a lower leakage...current than the conventional Schottky AlGaN/GaN HEMTs.1–3 Among a large number of insulator materials, an Al2O3 dielectric layer, deposited by...atomic layer deposition (ALD), is often employed as the gate insulator because of a large band gap (and the resultant high conduction band offset on

Image degradation by glare in radiologic display devices

NASA Astrophysics Data System (ADS)

Badano, Aldo; Flynn, Michael J.

1997-05-01

No electronic devices are currently available that can display digital radiographs without loss of visual information compared to traditional transilluminated film. Light scattering within the glass faceplate of cathode-ray tube (CRT) devices causes excessive glare that reduces image contrast. This glare, along with ambient light reflection, has been recognized as a significant limitation for radiologic applications. Efforts to control the effect of glare and ambient light reflection in CRTs include the use of absorptive glass and thin film coatings. In the near future, flat panel displays (FPD) with thin emissive structures should provide very low glare, high performance devices. We have used an optical Monte Carlo simulation to evaluate the effect of glare on image quality for typical CRT and flat panel display devices. The trade-off between display brightness and image contrast is described. For CRT systems, achieving good glare ratio requires a reduction of brightness to 30-40 percent of the maximum potential brightness. For FPD systems, similar glare performance can be achieved while maintaining 80 percent of the maximum potential brightness.

Growth and Characterisation of GaAs/AlGaAs Core-shell Nanowires for Optoelectronic Device Applications

NASA Astrophysics Data System (ADS)

Jiang, Nian

III-V semiconductor nanowires have been investigated as key components for future electronic and optoelectronic devices and systems due to their direct band gap and high electron mobility. Amongst the III-V semiconductors, the planar GaAs material system has been extensively studied and used in industries. Accordingly, GaAs nanowires are the prime candidates for nano-scale devices. However, the electronic performance of GaAs nanowires has yet to match that of state-of-the-art planar GaAs devices. The present deficiency of GaAs nanowires is typically attributed to the large surface-to- volume ratio and the tendency for non-radiative recombination centres to form at the surface. The favoured solution of this problem is by coating GaAs nanowires with AlGaAs shells, which replaces the GaAs surface with GaAs/AlGaAs interface. This thesis presents a systematic study of GaAs/AlGaAs core-shell nanowires grown by metal organic chemical vapour deposition (MOCVD), including understanding the growth, and characterisation of their structural and optical properties. The structures of the nanowires were mainly studied by scanning electron microscopy and transmis- sion electron microscopy (TEM). A procedure of microtomy was developed to prepare the cross-sectional samples for the TEM studies. The optical properties were charac- terised by photoluminescence (PL) spectroscopy. Carrier lifetimes were measured by time-resolved PL. The growth of AlGaAs shell was optimised to obtain the best optical properties, e.g. the strongest PL emission and the longest minority carrier lifetimes. (Abstract shortened by ProQuest.).

Amorphous oxides as electron transport layers in Cu(In,Ga)Se 2 superstrate devices: Amorphous oxides in Cu(In,Ga)Se 2 superstrate devices

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

Heinemann, M. D.; van Hest, M. F. A. M.; Contreras, M.

Cu(In,Ga)Se2 (CIGS) solar cells in superstrate configuration promise improved light management and higher stability compared to substrate devices, but they have yet to deliver comparable power conversion efficiencies (PCEs). Chemical reactions between the CIGS layer and the front contact were shown in the past to deteriorate the p-n junction in superstrate devices, which led to lower efficiencies compared to the substrate-type devices. This work aims to solve this problem by identifying a buffer layer between the CIGS layer and the front contact, acting as the electron transport layer, with an optimized electron affinity, doping density and chemical stability. Using combinatorialmore » material exploration we identified amorphous gallium oxide (a-GaOx) as a potentially suitable buffer layer material. The best results were obtained for a-GaOx with an electron affinity that was found to be comparable to that of CIGS. Based on the results of device simulations, it is assumed that detrimental interfacial acceptor states are present at the interface between CIGS and a-GaOx. However, these initial experiments indicate the potential of a-GaOx in this application, and how to reach performance parity with substrate devices, by further increase of its n-type doping density.« less

Flexible Display and Integrated Communication Devices (FDICD) Technology. Volume 2

DTIC Science & Technology

2008-06-01

AFRL-RH-WP-TR-2008-0072 Flexible Display and Integrated Communication Devices (FDICD) Technology, Volume II David Huffman Keith Tognoni...14 April 2004 – 20 June 2008 4. TITLE AND SUBTITLE Flexible Display and Integrated Communication Devices (FDICD) Technology, Volume II 5a...14. ABSTRACT This flexible display and integrated communication devices (FDICD) technology program sought to create a family of powerful

Design of thin InGaAsN(Sb) n-i-p junctions for use in four-junction concentrating photovoltaic devices

NASA Astrophysics Data System (ADS)

Wilkins, Matthew M.; Gupta, James; Jaouad, Abdelatif; Bouzazi, Boussairi; Fafard, Simon; Boucherif, Abderraouf; Valdivia, Christopher E.; Arès, Richard; Aimez, Vincent; Schriemer, Henry P.; Hinzer, Karin

2017-04-01

Four-junction solar cells for space and terrestrial applications require a junction with a band gap of ˜1 eV for optimal performance. InGaAsN or InGaAsN(Sb) dilute nitride junctions have been demonstrated for this purpose, but in achieving the 14 mA/cm2 short-circuit current needed to match typical GaInP and GaAs junctions, the open-circuit voltage (VOC) and fill factor of these junctions are compromised. In multijunction devices incorporating materials with short diffusion lengths, we study the use of thin junctions to minimize sensitivity to varying material quality and ensure adequate transmission into lower junctions. An n-i-p device with 0.65-μm absorber thickness has sufficient short-circuit current, however, it relies less heavily on field-aided collection than a device with a 1-μm absorber. Our standard cell fabrication process, which includes a rapid thermal anneal of the contacts, yields a significant improvement in diffusion length and device performance. By optimizing a four-junction cell around a smaller 1-sun short-circuit current of 12.5 mA/cm2, we produced an InGaAsN(Sb) junction with open-circuit voltage of 0.44 V at 1000 suns (1 sun=100 mW/cm2), diode ideality factor of 1.4, and sufficient light transmission to allow >12.5 mA/cm2 in all four subcells.

Proton-Induced Conductivity Enhancement in AlGaN/GaN HEMT Devices

NASA Astrophysics Data System (ADS)

Lee, In Hak; Lee, Chul; Choi, Byoung Ki; Yun, Yeseul; Chang, Young Jun; Jang, Seung Yup

2018-04-01

We investigated the influence of proton irradiation on the AlGaN/GaN high-electron-mobility transistor (HEMT) devices. Unlike previous studies on the degradation behavior upon proton irradiation, we observed improvements in their electrical conductivity and carrier concentration of up to 25% for the optimal condition. As we increased the proton dose, the carrier concentration and the mobility showed a gradual increase and decrease, respectively. From the photoluminescence measurements, we observed a reduction in the near-band-edge peak of GaN ( 366 nm), which correlate on the observed electrical properties. However, neither the Raman nor the X-ray diffraction analysis showed any changes, implying a negligible influence of protons on the crystal structures. We demonstrated that high-energy proton irradiation could be utilized to modify the transport properties of HEMT devices without damaging their crystal structures.

76 FR 29006 - In the Matter of Certain Motion-Sensitive Sound Effects Devices and Image Display Devices and...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-19

... Effects Devices and Image Display Devices and Components and Products Containing Same; Notice of... United States after importation of certain motion-sensitive sound effects devices and image display... devices and image display devices and components and products containing same that infringe one or more of...

Ocular Tolerance of Contemporary Electronic Display Devices.

PubMed

Clark, Andrew J; Yang, Paul; Khaderi, Khizer R; Moshfeghi, Andrew A

2018-05-01

Electronic displays have become an integral part of life in the developed world since the revolution of mobile computing a decade ago. With the release of multiple consumer-grade virtual reality (VR) and augmented reality (AR) products in the past 2 years utilizing head-mounted displays (HMDs), as well as the development of low-cost, smartphone-based HMDs, the ability to intimately interact with electronic screens is greater than ever. VR/AR HMDs also place the display at much closer ocular proximity than traditional electronic devices while also isolating the user from the ambient environment to create a "closed" system between the user's eyes and the display. Whether the increased interaction with these devices places the user's retina at higher risk of damage is currently unclear. Herein, the authors review the discovery of photochemical damage of the retina from visible light as well as summarize relevant clinical and preclinical data regarding the influence of modern display devices on retinal health. Multiple preclinical studies have been performed with modern light-emitting diode technology demonstrating damage to the retina at modest exposure levels, particularly from blue-light wavelengths. Unfortunately, high-quality in-human studies are lacking, and the small clinical investigations performed to date have failed to keep pace with the rapid evolutions in display technology. Clinical investigations assessing the effect of HMDs on human retinal function are also yet to be performed. From the available data, modern consumer electronic displays do not appear to pose any acute risk to vision with average use; however, future studies with well-defined clinical outcomes and illuminance metrics are needed to better understand the long-term risks of cumulative exposure to electronic displays in general and with "closed" VR/AR HMDs in particular. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:346-354.]. Copyright 2018, SLACK Incorporated.

Buffer Layer Effects on Tandem InGaAs TPV Devices

NASA Technical Reports Server (NTRS)

Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

2004-01-01

Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

Interactive display system having a digital micromirror imaging device

DOEpatents

Veligdan, James T.; DeSanto, Leonard; Kaull, Lisa; Brewster, Calvin

2006-04-11

A display system includes a waveguide optical panel having an inlet face and an opposite outlet face. A projector cooperates with a digital imaging device, e.g. a digital micromirror imaging device, for projecting an image through the panel for display on the outlet face. The imaging device includes an array of mirrors tiltable between opposite display and divert positions. The display positions reflect an image light beam from the projector through the panel for display on the outlet face. The divert positions divert the image light beam away from the panel, and are additionally used for reflecting a probe light beam through the panel toward the outlet face. Covering a spot on the panel, e.g. with a finger, reflects the probe light beam back through the panel toward the inlet face for detection thereat and providing interactive capability.

GaN light-emitting device based on ionic liquid electrolyte

NASA Astrophysics Data System (ADS)

Hirai, Tomoaki; Sakanoue, Tomo; Takenobu, Taishi

2018-06-01

Ionic liquids (ILs) are attractive materials for fabricating unique hybrid devices based on electronics and electrochemistry; thus, IL-gated transistors and organic light-emitting devices of light-emitting electrochemical cells (LECs) are investigated for future low-voltage and high-performance devices. In LECs, voltage application induces the formation of electrochemically doped p–n homojunctions owing to ion rearrangements in composites of semiconductors and electrolytes, and achieves electron–hole recombination for light emission at the homojunctions. In this work, we applied this concept of IL-induced electrochemical doping to the fabrication of GaN-based light-emitting devices. We found that voltage application to the layered IL/GaN structure accumulated electrons on the GaN surface owing to ion rearrangements and improved the conductivity of GaN. The ion rearrangement also enabled holes to be injected by the strong electric field of electric double layers on hole injection contacts. This simultaneous injection of holes and electrons into GaN mediated by ions achieves light emission at a low voltage of around 3.4 V. The light emission from the simple IL/GaN structure indicates the usefulness of an electrochemical technique in generating light emission with great ease of fabrication.

Low-frequency noise in AlN/AlGaN/GaN metal-insulator-semiconductor devices: A comparison with Schottky devices

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

Le, Son Phuong; Nguyen, Tuan Quy; Shih, Hong-An

2014-08-07

We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) devices, where the AlN gate insulator layer was sputtering-deposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in the MIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters α for the gated regionmore » as a function of the sheet electron concentration n{sub s} under the gate. In a regime of small n{sub s}, both the MIS- and Schottky-HFETs exhibit α∝n{sub s}{sup −1}. On the other hand, in a middle n{sub s} regime of the MIS-HFETs, α decreases rapidly like n{sub s}{sup −ξ} with ξ ∼ 2-3, which is not observed for the Schottky-HFETs. In addition, we observe strong increase in α∝n{sub s}{sup 3} in a large n{sub s} regime for both the MIS- and Schottky-HFETs.« less

Metal-oxide-semiconductor devices using Ga2O3 dielectrics on n-type GaN

NASA Astrophysics Data System (ADS)

Lee, Ching-Ting; Chen, Hong-Wei; Lee, Hsin-Ying

2003-06-01

Using a photoelectrochemical method involving a He-Cd laser, Ga2O3 oxide layers were directly grown on n-type GaN. We demonstrated the performance of the resultant metal-oxide-semiconductor devices based on the grown Ga2O3 layer. An extremely low reverse leakage current of 200 pA was achieved when devices operated at -20 V. Furthermore, high forward and reverse breakdown electric fields of 2.80 MV/cm and 5.70 MV/cm, respectively, were obtained. Using a photoassisted current-voltage method, a low interface state density of 2.53×1011 cm-2 eV-1 was estimated. The varactor devices permit formation of inversion layers, so that they may be applied for the fabrication of metal-oxide-semiconductor field-effect transistors.

Non-binary Colour Modulation for Display Device Based on Phase Change Materials.

PubMed

Ji, Hong-Kai; Tong, Hao; Qian, Hang; Hui, Ya-Juan; Liu, Nian; Yan, Peng; Miao, Xiang-Shui

2016-12-19

A reflective-type display device based on phase change materials is attractive because of its ultrafast response time and high resolution compared with a conventional display device. This paper proposes and demonstrates a unique display device in which multicolour changing can be achieved on a single device by the selective crystallization of double layer phase change materials. The optical contrast is optimized by the availability of a variety of film thicknesses of two phase change layers. The device exhibits a low sensitivity to the angle of incidence, which is important for display and colour consistency. The non-binary colour rendering on a single device is demonstrated for the first time using optical excitation. The device shows the potential for ultrafast display applications.

[Microcomputer control of a LED stimulus display device].

PubMed

Ohmoto, S; Kikuchi, T; Kumada, T

1987-02-01

A visual stimulus display system controlled by a microcomputer was constructed at low cost. The system consists of a LED stimulus display device, a microcomputer, two interface boards, a pointing device (a "mouse") and two kinds of software. The first software package is written in BASIC. Its functions are: to construct stimulus patterns using the mouse, to construct letter patterns (alphabet, digit, symbols and Japanese letters--kanji, hiragana, katakana), to modify the patterns, to store the patterns on a floppy disc, to translate the patterns into integer data which are used to display the patterns in the second software. The second software package, written in BASIC and machine language, controls display of a sequence of stimulus patterns in predetermined time schedules in visual experiments.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1979-01-01

The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

Review of GaN-based devices for terahertz operation

NASA Astrophysics Data System (ADS)

Ahi, Kiarash

2017-09-01

GaN provides the highest electron saturation velocity, breakdown voltage, operation temperature, and thus the highest combined frequency-power performance among commonly used semiconductors. The industrial need for compact, economical, high-resolution, and high-power terahertz (THz) imaging and spectroscopy systems are promoting the utilization of GaN for implementing the next generation of THz systems. As it is reviewed, the mentioned characteristics of GaN together with its capabilities of providing high two-dimensional election densities and large longitudinal optical phonon of ˜90 meV make it one of the most promising semiconductor materials for the future of the THz emitters, detectors, mixers, and frequency multiplicators. GaN-based devices have shown capabilities of operation in the upper THz frequency band of 5 to 12 THz with relatively high photon densities in room temperature. As a result, THz imaging and spectroscopy systems with high resolution and deep depth of penetration can be realized through utilizing GaN-based devices. A comprehensive review of the history and the state of the art of GaN-based electronic devices, including plasma heterostructure field-effect transistors, negative differential resistances, hetero-dimensional Schottky diodes, impact avalanche transit times, quantum-cascade lasers, high electron mobility transistors, Gunn diodes, and tera field-effect transistors together with their impact on the future of THz imaging and spectroscopy systems is provided.

Strain effects in low-dimensional silicon MOS and AlGaN/GaN HEMT devices

NASA Astrophysics Data System (ADS)

Baykan, Mehmet Onur

Strained silicon technology is a well established method to enhance sub-100nm MOSFET performance. With the scalability of process-induced strain, strained silicon channels have been used in every advanced CMOS technology since the 90nm node. At the 22nm node, due to the detrimental short channel effects, non-planar silicon CMOS has emerged as a viable solution to sustain transistor scaling without compromising the device performance. Therefore, it is necessary to conduct a physics based investigation of the effects of mechanical strain in silicon MOS device performance enhancement, as the transverse and longitudinal device dimensions scale down for future technology nodes. While silicon is widely used as the material basis for logic transistors, AlGaN/GaN HEMTs promise a superior device platform over silicon based power MOSFETs for high-frequency and high-power applications. In contrast to the mature Si crystal growth technology, the abundance of defects in the GaN material system creates obstacles for the realization of a reliable AlGaN/GaN HEMT device technology. Due to the high levels of internal mechanical strain present in AlGaN/GaN HEMTs, it is of utmost importance to understand the impact of mechanical stress on AlGaN/GaN trap generation. First, we have investigated the underlying physics of the comparable electron mobility observed in (100) and (110) sidewall silicon double-gate FinFETs, which is different from the observed planar (100) and (110) electron mobility. By conducting a systematic experimental study, it is shown that the undoped body, metal gate induced stress, and volume-inversion effects do not explain the comparable electron mobility. Using a self-consistent double-gate FinFET simulator, we have showed that for (110) FinFETs, an increased population of electrons is obtained for the Delta2 valley due to the heavy nonparabolic confinement mass, leading to a comparable average electron transport effective mass for both orientations. The width

GaN Nanowire Devices: Fabrication and Characterization

NASA Astrophysics Data System (ADS)

Scott, Reum

The development of microelectronics in the last 25 years has been characterized by an exponential increase of the bit density in integrated circuits (ICs) with time. Scaling solid-state devices improves cost, performance, and power; as such, it is of particular interest for companies, who gain a market advantage with the latest technology. As a result, the microelectronics industry has driven transistor feature size scaling from 10 μm to ~30 nm during the past 40 years. This trend has persisted for 40 years due to optimization, new processing techniques, device structures, and materials. But when noting processor speeds from the 1970's to 2009 and then again in 2010, the implication would be that the trend has ceased. To address the challenge of shrinking the integrated circuit (IC), current research is centered on identifying new materials and devices that can supplement and/or potentially supplant it. Bottom-up methods tailor nanoscale building blocks---atoms, molecules, quantum dots, and nanowires (NWs)---to be used to overcome these limitations. The Group IIIA nitrides (InN, AlN, and GaN) possess appealing properties such as a direct band gap spanning the whole solar spectrum, high saturation velocity, and high breakdown electric field. As a result nanostructures and nanodevices made from GaN and related nitrides are suitable candidates for efficient nanoscale UV/ visible light emitters, detectors, and gas sensors. To produce devices with such small structures new fabrication methods must be implemented. Devices composed of GaN nanowires were fabricated using photolithography and electron beam lithography. The IV characteristics of these devices were noted under different illuminations and the current tripled from 4.8*10-7 A to 1.59*10 -6 A under UV light which persisted for at least 5hrs.

A device-dependent interface for interactive image display

NASA Technical Reports Server (NTRS)

Perkins, D. C.; Szczur, M. R.; Owings, J.; Jamros, R. K.

1984-01-01

The structure of the device independent Display Management Subsystem (DMS) and the interface routines that are available to the applications programmer for use in developing a set of portable image display utility programs are described.

Long-term stability assessment of AlGaN/GaN field effect transistors modified with peptides: Device characteristics vs. surface properties

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

Rohrbaugh, Nathaniel; Bryan, Isaac; Bryan, Zachary

AlGaN/GaN Field Effect Transistors (FETs) are promising biosensing devices. Functionalization of these devices is explored in this study using an in situ approach with phosphoric acid etchant and a phosphonic acid derivative. Devices are terminated on peptides and soaked in water for up to 168 hrs to examine FETs for both device responses and surface chemistry changes. Measurements demonstrated threshold voltage shifting after the functionalization and soaking processes, but demonstrated stable FET behavior throughout. X-ray photoelectron spectroscopy and atomic force microscopy confirmed peptides attachment to device surfaces before and after water soaking. Results of this work point to the stabilitymore » of peptide coated functionalized AlGaN/GaN devices in solution and support further research of these devices as disposable, long term, in situ biosensors.« less

1000 X difference between current displays and capability of human visual system: payoff potential for affordable defense systems

NASA Astrophysics Data System (ADS)

Hopper, Darrel G.

2000-08-01

Displays were invented just in the last century. The human visual system evolved over millions of years. The disparity between the natural world 'display' and that 'sampled' by year 2000 technology is more than a factor of one million. Over 1000X of this disparity between the fidelity of current electronic displays and human visual capacity is in 2D resolution alone. Then there is true 3D, which adds an additional factor of over 1000X. The present paper focuses just on the 2D portion of this grand technology challenge. Should a significant portion of this gap be closed, say just 10X by 2010, display technology can help drive a revolution in military affairs. Warfighter productivity must grow dramatically, and improved display technology systems can create a critical opportunity to increase defense capability while decreasing crew sizes.

Incomplete Ionization of a 110 meV Unintentional Donor in β-Ga2O3 and its Effect on Power Devices.

PubMed

Neal, Adam T; Mou, Shin; Lopez, Roberto; Li, Jian V; Thomson, Darren B; Chabak, Kelson D; Jessen, Gregg H

2017-10-16

Understanding the origin of unintentional doping in Ga 2 O 3 is key to increasing breakdown voltages of Ga 2 O 3 based power devices. Therefore, transport and capacitance spectroscopy studies have been performed to better understand the origin of unintentional doping in Ga 2 O 3 . Previously unobserved unintentional donors in commercially available [Formula: see text] Ga 2 O 3 substrates have been electrically characterized via temperature dependent Hall effect measurements up to 1000 K and found to have a donor energy of 110 meV. The existence of the unintentional donor is confirmed by temperature dependent admittance spectroscopy, with an activation energy of 131 meV determined via that technique, in agreement with Hall effect measurements. With the concentration of this donor determined to be in the mid to high 10 16  cm -3 range, elimination of this donor from the drift layer of Ga 2 O 3 power electronics devices will be key to pushing the limits of device performance. Indeed, analytical assessment of the specific on-resistance (R onsp ) and breakdown voltage of Schottky diodes containing the 110 meV donor indicates that incomplete ionization increases R onsp and decreases breakdown voltage as compared to Ga 2 O 3 Schottky diodes containing only the shallow donor. The reduced performance due to incomplete ionization occurs in addition to the usual tradeoff between R onsp and breakdown voltage.

Display device-adapted video quality-of-experience assessment

NASA Astrophysics Data System (ADS)

Rehman, Abdul; Zeng, Kai; Wang, Zhou

2015-03-01

Today's viewers consume video content from a variety of connected devices, including smart phones, tablets, notebooks, TVs, and PCs. This imposes significant challenges for managing video traffic efficiently to ensure an acceptable quality-of-experience (QoE) for the end users as the perceptual quality of video content strongly depends on the properties of the display device and the viewing conditions. State-of-the-art full-reference objective video quality assessment algorithms do not take into account the combined impact of display device properties, viewing conditions, and video resolution while performing video quality assessment. We performed a subjective study in order to understand the impact of aforementioned factors on perceptual video QoE. We also propose a full reference video QoE measure, named SSIMplus, that provides real-time prediction of the perceptual quality of a video based on human visual system behaviors, video content characteristics (such as spatial and temporal complexity, and video resolution), display device properties (such as screen size, resolution, and brightness), and viewing conditions (such as viewing distance and angle). Experimental results have shown that the proposed algorithm outperforms state-of-the-art video quality measures in terms of accuracy and speed.

Blue light effect on retinal pigment epithelial cells by display devices.

PubMed

Moon, Jiyoung; Yun, Jieun; Yoon, Yeo Dae; Park, Sang-Il; Seo, Young-Jun; Park, Won-Sang; Chu, Hye Yong; Park, Keun Hong; Lee, Myung Yeol; Lee, Chang Woo; Oh, Soo Jin; Kwak, Young-Shin; Jang, Young Pyo; Kang, Jong Soon

2017-05-22

Blue light has high photochemical energy and induces cell apoptosis in retinal pigment epithelial cells. Due to its phototoxicity, retinal hazard by blue light stimulation has been well demonstrated using high intensity light sources. However, it has not been studied whether blue light in the displays, emitting low intensity light, such as those used in today's smartphones, monitors, and TVs, also causes apoptosis in retinal pigment epithelial cells. We attempted to examine the blue light effect on human adult retinal epithelial cells using display devices with different blue light wavelength ranges, the peaks of which specifically appear at 449 nm, 458 nm, and 470 nm. When blue light was illuminated on A2E-loaded ARPE-19 cells using these displays, the display with a blue light peak at a shorter wavelength resulted in an increased production of reactive oxygen species (ROS). Moreover, the reduction of cell viability and induction of caspase-3/7 activity were more evident in A2E-loaded ARPE-19 cells after illumination by the display with a blue light peak at a shorter wavelength, especially at 449 nm. Additionally, white light was tested to examine the effect of blue light in a mixed color illumination with red and green lights. Consistent with the results obtained using only blue light, white light illuminated by display devices with a blue light peak at a shorter wavelength also triggered increased cell death and apoptosis compared to that illuminated by display devices with a blue light peak at longer wavelength. These results show that even at the low intensity utilized in the display devices, blue light can induce ROS production and apoptosis in retinal cells. Our results also suggest that the blue light hazard of display devices might be highly reduced if the display devices contain less short wavelength blue light.

Characterization and device performance of (AgCu)(InGa)Se2 absorber layers

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

Hanket, Gregory; Boyle, Jonathan H.; Shafarman, William N.

The study of (AgCu)(InGa)Se2 absorber layers is of interest in that Ag-chalcopyrites exhibit both wider bandgaps and lower melting points than their Cu counterparts. (AgCu)(InGa)Se2 absorber layers were deposited over the composition range 0 < Ag/(Ag+Cu) < 1 and 0.3 < Ga/(In+Ga) < 1.0 using a variety of elemental co-evaporation processes. Films were found to be singlephase over the entire composition range, in contrast to prior studies. Devices with Ga content 0.3 < Ga/(In+Ga) <0.5 tolerated Ag incorporation up to Ag/(Ag+Cu) = 0.5 without appreciable performance loss. Ag-containing films with Ga/(In+Ga) = 0.8 showed improved device characteristics over Cu-only controlmore » samples, in particular a 30-40% increase in short-circuit current. An absorber layer with composition Ag/(Ag+Cu) = 0.75 and Ga/(In+Ga) = 0.8 yielded a device with VOC = 890 mV, JSC = 20.5mA/cm2, fill factor = 71.3%, and η = 13.0%.« less

Conductivity based on selective etch for GaN devices and applications thereof

DOEpatents

Zhang, Yu; Sun, Qian; Han, Jung

2015-12-08

This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

Control of Ga-oxide interlayer growth and Ga diffusion in SiO2/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliability

NASA Astrophysics Data System (ADS)

Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Yamada, Hisashi; Takahashi, Tokio; Shimizu, Mitsuaki; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-01-01

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO2/GaO x /GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 1010 cm-2 eV-1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.

GaN-on-diamond electronic device reliability: Mechanical and thermo-mechanical integrity

NASA Astrophysics Data System (ADS)

Liu, Dong; Sun, Huarui; Pomeroy, James W.; Francis, Daniel; Faili, Firooz; Twitchen, Daniel J.; Kuball, Martin

2015-12-01

The mechanical and thermo-mechanical integrity of GaN-on-diamond wafers used for ultra-high power microwave electronic devices was studied using a micro-pillar based in situ mechanical testing approach combined with an optical investigation of the stress and heat transfer across interfaces. We find the GaN/diamond interface to be thermo-mechanically stable, illustrating the potential for this material for reliable GaN electronic devices.

Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

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

Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi

2015-08-15

Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originatedmore » from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.« less

On-chip photonic system using suspended p-n junction InGaN/GaN multiple quantum wells device and multiple waveguides

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

Wang, Yongjin, E-mail: wangyj@njupt.edu.cn; Zhu, Guixia; Gao, Xumin

We propose, fabricate, and characterize the on-chip integration of suspended p-n junction InGaN/GaN multiple quantum wells (MQWs) device and multiple waveguides on the same GaN-on-silicon platform. The integrated devices are fabricated via a wafer-level process and exhibit selectable functionalities for diverse applications. As the suspended p-n junction InGaN/GaN MQWs device operates under a light emitting diode (LED) mode, part of the light emission is confined and guided by the suspended waveguides. The in-plane propagation along the suspended waveguides is measured by a micro-transmittance setup. The on-chip data transmission is demonstrated for the proof-of-concept photonic integration. As the suspended p-n junctionmore » InGaN/GaN MQWs device operates under photodiode mode, the light is illuminated on the suspended waveguides with the aid of the micro-transmittance setup and, thus, coupled into the suspended waveguides. The guided light is finally sensed by the photodiode, and the induced photocurrent trace shows a distinct on/off switching performance. These experimental results indicate that the on-chip photonic integration is promising for the development of sophisticated integrated photonic circuits in the visible wavelength region.« less

A graphene/single GaAs nanowire Schottky junction photovoltaic device.

PubMed

Luo, Yanbin; Yan, Xin; Zhang, Jinnan; Li, Bang; Wu, Yao; Lu, Qichao; Jin, Chenxiaoshuai; Zhang, Xia; Ren, Xiaomin

2018-05-17

A graphene/nanowire Schottky junction is a promising structure for low-cost high-performance optoelectronic devices. Here we demonstrate a graphene/single GaAs nanowire Schottky junction photovoltaic device. The Schottky junction is fabricated by covering a single layer graphene onto an n-doped GaAs nanowire. Under 532 nm laser excitation, the device exhibits a high responsivity of 231 mA W-1 and a short response/recover time of 85/118 μs at zero bias. Under AM 1.5 G solar illumination, the device has an open-circuit voltage of 75.0 mV and a short-circuit current density of 425 mA cm-2, yielding a remarkable conversion efficiency of 8.8%. The excellent photovoltaic performance of the device is attributed to the strong built-in electric field in the Schottky junction as well as the transparent property of graphene. The device is promising for self-powered high-speed photodetectors and low-cost high-efficiency solar cells.

Tactile display device using an electrorheological fluid

NASA Technical Reports Server (NTRS)

Garner, H. Douglas (Inventor)

1994-01-01

A tactile display device utilizes an electrorheological fluid to activate a plurality of tactile dots. A voltage is selectively produced uniformly across an electrorheological fluid flowing between a common ground electrode and a plurality of conductive dot electrodes, thereby producing an increase in the fluid's viscosity to the extent that fluid flow between the two electrodes is restricted. The flow restriction produces a build-up of electrorheological fluid in a corresponding dot actuator chamber. The resulting pressure increase in the chamber displaces an elastic diaphragm fixed to a display surface to form a lump which can be perceived by the reader as one dot in a Braille character cell. A flow regulation system provides a continually pressurized flow system and provides for free flow of the electrorheological fluid through the plurality of dot actuator chambers when they are not activated. The device is adaptable to printed circuit techniques and can simultaneously display tactile dots representative of a full page of Braille characters stored on a medium such as a tape cassette or to display tactile dots representative of non-Braille data appearing on a computer monitor or contained on another data storage medium. In an alternate embodiment, the elastic diaphragm drives a plurality of spring-loaded pins provided with positive stops to maintain consistent displacements of the pins in both their actuated and nonactuated positions.

Display challenges resulting from the use of wide field of view imaging devices

NASA Astrophysics Data System (ADS)

Petty, Gregory J.; Fulton, Jack; Nicholson, Gail; Seals, Ean

2012-06-01

As focal plane array technologies advance and imagers increase in resolution, display technology must outpace the imaging improvements in order to adequately represent the complete data collection. Typical display devices tend to have an aspect ratio similar to 4:3 or 16:9, however a breed of Wide Field of View (WFOV) imaging devices exist that skew from the norm with aspect ratios as high as 5:1. This particular quality, when coupled with a high spatial resolution, presents a unique challenge for display devices. Standard display devices must choose between resizing the image data to fit the display and displaying the image data in native resolution and truncating potentially important information. The problem compounds when considering the applications; WFOV high-situationalawareness imagers are sought for space-limited military vehicles. Tradeoffs between these issues are assessed to the image quality of the WFOV sensor.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1985-01-01

The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

Integration Head Mounted Display Device and Hand Motion Gesture Device for Virtual Reality Laboratory

NASA Astrophysics Data System (ADS)

Rengganis, Y. A.; Safrodin, M.; Sukaridhoto, S.

2018-01-01

Virtual Reality Laboratory (VR Lab) is an innovation for conventional learning media which show us whole learning process in laboratory. There are many tools and materials are needed by user for doing practical in it, so user could feel new learning atmosphere by using this innovation. Nowadays, technologies more sophisticated than before. So it would carry in education and it will be more effective, efficient. The Supported technologies are needed us for making VR Lab such as head mounted display device and hand motion gesture device. The integration among them will be used us for making this research. Head mounted display device for viewing 3D environment of virtual reality laboratory. Hand motion gesture device for catching user real hand and it will be visualized in virtual reality laboratory. Virtual Reality will show us, if using the newest technologies in learning process it could make more interesting and easy to understand.

Flexible GaN for High Performance, Strainable Radio Frequency Devices (Postprint)

DTIC Science & Technology

2017-11-02

devices on van der Waals (vdW) layers has been facilitated by the recent avail - ability of high -quality atomically smooth BN and graphene epi- taxial...AFRL-RX-WP-JA-2017-0333 FLEXIBLE GaN FOR HIGH PERFORMANCE, STRAINABLE RADIO FREQUENCY DEVICES (POSTPRINT) Elizabeth A. Moore and Timothy...2. REPORT TYPE 3. DATES COVERED (From - To) 5 April 2017 Interim 8 September 2014 – 5 March 2017 4. TITLE AND SUBTITLE FLEXIBLE GaN FOR HIGH

Accelerated life testing and temperature dependence of device characteristics in GaAs CHFET devices

NASA Technical Reports Server (NTRS)

Gallegos, M.; Leon, R.; Vu, D. T.; Okuno, J.; Johnson, A. S.

2002-01-01

Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.

Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

NASA Astrophysics Data System (ADS)

Su, Ming; Chen, Chingchi; Rajan, Siddharth

2013-07-01

GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600-1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

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

Rogers, John A.; Nuzzo, Ralph; Kim, Hoon-sik

Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

DOEpatents

Rogers, John A; Nuzzo, Ralph; Kim, Hoon-sik; Brueckner, Eric; Park, Sang Il; Kim, Rak Hwan

2014-10-21

Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Long-lived and highly efficient green and blue phosphorescent emitters and device architectures for OLED displays

NASA Astrophysics Data System (ADS)

Eickhoff, Christian; Murer, Peter; Geßner, Thomas; Birnstock, Jan; Kröger, Michael; Choi, Zungsun; Watanabe, Soichi; May, Falk; Lennartz, Christian; Stengel, Ilona; Münster, Ingo; Kahle, Klaus; Wagenblast, Gerhard; Mangold, Hannah

2015-09-01

In this paper, two OLED device concepts are introduced. First, classical phosphorescent green carbene emitters with unsurpassed lifetime, combined with low voltage and high efficiency are presented and the associated optimized OLED stacks are explained. Second, a path towards highly efficient, long-lived deep blue systems is shown. The high efficiencies can be reached by having the charge-recombination on the phosphorescent carbene emitter while at the same time short emissive lifetimes are realized by fast energy transfer to the fluorescent emitter, which eventually allows for higher OLED stability in the deep blue. Device architectures, materials and performance data are presented showing that carbene type emitters have the potential to outperform established phosphorescent green emitters both in terms of lifetime and efficiency. The specific class of green emitters under investigation shows distinctly larger electron affinities (2.1 to 2.5 eV) and ionization potentials (5.6 to 5.8 eV) as compared to the "standard" emitter Ir(ppy)3 (5.0/1.6 eV). This difference in energy levels requires an adopted OLED design, in particular with respect to emitter hosts and blocking layers. Consequently, in the diode setup presented here, the emitter species is electron transporting or electron trapping. For said green carbene emitters, the typical peak wavelength is 525 nm yielding CIE color coordinates of (x = 0.33, y = 0.62). Device data of green OLEDs are shown with EQEs of 26 %. Driving voltage at 1000 cd/m2 is below 3 V. In an optimized stack, a device lifetime of LT95 > 15,000 h (1000 cd/m2) has been reached, thus fulfilling AMOLED display requirements.

GaAs, AlAs, and AlxGa1-xAs: Material parameters for use in research and device applications

NASA Astrophysics Data System (ADS)

Adachi, Sadao

1985-08-01

The AlxGa1-xAs/GaAs heterostructure system is potentially useful material for high-speed digital, high-frequency microwave, and electro-optic device applications. Even though the basic AlxGa1-xAs/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters. Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J. S. Blakemore, J. Appl. Phys. 53, R123 (1982)]. The purpose of this review is (i) to obtain and clarify all the various material parameters of AlxGa1-xAs alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications. A complete set of material parameters are considered in this review for GaAs, AlAs, and AlxGa1-xAs alloys. The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs). The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic-band structure, (7) external perturbation effects on the band-gap energy, (8) effective mass, (9) deformation potential, (10) static and high-frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Fröhlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties. Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x. Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant

49 CFR 221.13 - Marking device display.

Code of Federal Regulations, 2010 CFR

2010-10-01

... visibility that the end silhouette of a standard box car cannot be seen from 1/2 mile on tangent track by a... with, (2) display on the trailing end of the rear car of that train, and (3) continuously illuminate or... cell activation mechanism complying with paragraph (c) of this section, the marking devices prescribed...

Noise characterization of enhancement-mode AlGaN graded barrier MIS-HEMT devices

NASA Astrophysics Data System (ADS)

Mohanbabu, A.; Saravana Kumar, R.; Mohankumar, N.

2017-12-01

This paper reports a systematic theoretical study on the microwave noise performance of graded AlGaN/GaN metal-insulator semiconductor high-electron mobility transistors (MIS-HEMTs) built on an Al2O3 substrate. The HfAlOx/AlGaN/GaN MIS-HEMT devices designed for this study show an outstanding small signal analog/RF and noise performance. The results on 1 μm gate length device show an enhancement mode operation with threshold voltage, VT = + 5.3 V, low drain leakage current, Ids,LL in the order of 1 × 10-9 A/mm along with high current gain cut-off frequency, fT of 17 GHz and maximum oscillation frequency fmax of 47 GHz at Vds = 10 V. The device Isbnd V and low-frequency noise estimation of the gate and drain noise spectral density and their correlation are evaluated using a Green's function method under different biasing conditions. The devices show a minimum noise figure (NFmin) of 1.053 dB in combination with equivalent noise resistance (Rn) of 23 Ω at 17 GHz, at Vgs = 6 V and Vds = 5 V which is relatively low and is suitable for broad-band low-noise amplifiers. This study shows that the graded AlGaN MIS-HEMT with HfAlOX gate insulator is appropriate for application requiring high-power and low-noise.

Investigation of HCl-based surface treatment for GaN devices

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

Okada, Hiroshi, E-mail: okada@ee.tut.ac.jp; Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580; Shinohara, Masatohi

2016-02-01

Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H{sub 2}O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treatedmore » samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.« less

Emi-Flective Display Device with Attribute of High Glare-Free-Ambient-Contrast-Ratio

NASA Astrophysics Data System (ADS)

Yang, Bo-Ru; Hsu, Chuan-Wei; Shieh, Han-Ping D.

2007-11-01

We have demonstrated the integration of an organic light emitting device (OLED) and a reflective liquid crystal display (R-LCD) which was termed an emi-flective display. The glare-free-ambient-contrast-ratio (GFA-CR) was used to evaluate the image quality of display devices under ambient light. Through integrating the OLED with R-LCD, the GFA-CR of the device achieved an improvement by a factor of 8 compared with that of the OLED alone. Moreover, the integrated R-LCD showed a GFA-CR of 100:1 within a viewing cone of 20° which can suppress the wash-out of OLED and is more power-saving in the sunlight. Therefore, an emi-flective display is a promising technique for mobile applications.

Influence of composition on the performance of sintered Cu(In,Ga)Se2 nanocrystal thin-film photovoltaic devices.

PubMed

Akhavan, Vahid A; Harvey, Taylor B; Stolle, C Jackson; Ostrowski, David P; Glaz, Micah S; Goodfellow, Brian W; Panthani, Matthew G; Reid, Dariya K; Vanden Bout, David A; Korgel, Brian A

2013-03-01

Thin-film photovoltaic devices (PVs) were prepared by selenization using oleylamine-capped Cu(In,Ga)Se2 (CIGS) nanocrystals sintered at a high temperature (>500 °C) under Se vapor. The device performance varied significantly with [Ga]/[In+Ga] content in the nanocrystals. The highest power conversion efficiency (PCE) observed in the devices studied was 5.1 % under air mass 1.5 global (AM 1.5 G) illumination, obtained with [Ga]/[In+Ga]=0.32. The variation in PCE with composition is partly a result of bandgap tuning and optimization, but the main influence of nanocrystal composition appeared to be on the quality of the sintered films. The [Cu]/[In+Ga] content was found to be strongly influenced by the [Ga]/[In+Ga] concentration, which appears to be correlated with the morphology of the sintered film. For this reason, only small changes in the [Ga]/[In+Ga] content resulted in significant variations in device efficiency. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flight Simulator Evaluation of Display Media Devices for Synthetic Vision Concepts

NASA Technical Reports Server (NTRS)

Arthur, J. J., III; Williams, Steven P.; Prinzel, Lawrence J., III; Kramer, Lynda J.; Bailey, Randall E.

2004-01-01

The Synthetic Vision Systems (SVS) Project of the National Aeronautics and Space Administration's (NASA) Aviation Safety Program (AvSP) is striving to eliminate poor visibility as a causal factor in aircraft accidents as well as enhance operational capabilities of all aircraft. To accomplish these safety and capacity improvements, the SVS concept is designed to provide a clear view of the world around the aircraft through the display of computer-generated imagery derived from an onboard database of terrain, obstacle, and airport information. Display media devices with which to implement SVS technology that have been evaluated so far within the Project include fixed field of view head up displays and head down Primary Flight Displays with pilot-selectable field of view. A simulation experiment was conducted comparing these display devices to a fixed field of view, unlimited field of regard, full color Helmet-Mounted Display system. Subject pilots flew a visual circling maneuver in IMC at a terrain-challenged airport. The data collected for this experiment is compared to past SVS research studies.

Nonpolar p-GaN/n-Si heterojunction diode characteristics: a comparison between ensemble and single nanowire devices

NASA Astrophysics Data System (ADS)

Patsha, Avinash; Pandian, Ramanathaswamy; Dhara, Sandip; Tyagi, A. K.

2015-10-01

The electrical and photodiode characteristics of ensemble and single p-GaN nanowire and n-Si heterojunction devices were studied. Ideality factor of the single nanowire p-GaN/n-Si device was found to be about three times lower compared to that of the ensemble nanowire device. Apart from the deep-level traps in p-GaN nanowires, defect states due to inhomogeneity in Mg dopants in the ensemble nanowire device are attributed to the origin of the high ideality factor. Photovoltaic mode of the ensemble nanowire device showed an improvement in the fill-factors up to 60% over the single nanowire device with fill-factors up to 30%. Responsivity of the single nanowire device in the photoconducting mode was found to be enhanced by five orders, at 470 nm. The enhanced photoresponse of the single nanowire device also confirms the photoconduction due to defect states in p-GaN nanowires.

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

Perspective: Toward efficient GaN-based red light emitting diodes using europium doping

NASA Astrophysics Data System (ADS)

Mitchell, Brandon; Dierolf, Volkmar; Gregorkiewicz, Tom; Fujiwara, Yasufumi

2018-04-01

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. The realization of this LED is crucial for the monolithic integration of the three primary colors and the development of nitride-based full-color high-resolution displays. In this perspective, we will address the challenges of attaining red luminescence from GaN under current injection and the methods that have been developed to circumvent them. While several approaches will be mentioned, a large emphasis will be placed on the recent developments of doping GaN with Eu3+ to achieve an efficient red GaN-based LED. Finally, we will provide an outlook to the future of this material as a candidate for small scale displays such as mobile device screens or micro-LED displays.

76 FR 72439 - Certain Consumer Electronics and Display Devices and Products Containing Same; Receipt of...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-23

... INTERNATIONAL TRADE COMMISSION [DN 2858] Certain Consumer Electronics and Display Devices and.... International Trade Commission has received a complaint entitled In Re Certain Consumer Electronics and Display... importation of certain consumer electronics and display devices and products containing same. The complaint...

M-plane core-shell InGaN/GaN multiple-quantum-wells on GaN wires for electroluminescent devices.

PubMed

Koester, Robert; Hwang, Jun-Seok; Salomon, Damien; Chen, Xiaojun; Bougerol, Catherine; Barnes, Jean-Paul; Dang, Daniel Le Si; Rigutti, Lorenzo; de Luna Bugallo, Andres; Jacopin, Gwénolé; Tchernycheva, Maria; Durand, Christophe; Eymery, Joël

2011-11-09

Nonpolar InGaN/GaN multiple quantum wells (MQWs) grown on the {11-00} sidewalls of c-axis GaN wires have been grown by organometallic vapor phase epitaxy on c-sapphire substrates. The structural properties of single wires are studied in detail by scanning transmission electron microscopy and in a more original way by secondary ion mass spectroscopy to quantify defects, thickness (1-8 nm) and In-composition in the wells (∼16%). The core-shell MQW light emission characteristics (390-420 nm at 5 K) were investigated by cathodo- and photoluminescence demonstrating the absence of the quantum Stark effect as expected due to the nonpolar orientation. Finally, these radial nonpolar quantum wells were used in room-temperature single-wire electroluminescent devices emitting at 392 nm by exploiting sidewall emission.

Noise tolerant illumination optimization applied to display devices

NASA Astrophysics Data System (ADS)

Cassarly, William J.; Irving, Bruce

2005-02-01

Display devices have historically been designed through an iterative process using numerous hardware prototypes. This process is effective but the number of iterations is limited by the time and cost to make the prototypes. In recent years, virtual prototyping using illumination software modeling tools has replaced many of the hardware prototypes. Typically, the designer specifies the design parameters, builds the software model, predicts the performance using a Monte Carlo simulation, and uses the performance results to repeat this process until an acceptable design is obtained. What is highly desired, and now possible, is to use illumination optimization to automate the design process. Illumination optimization provides the ability to explore a wider range of design options while also providing improved performance. Since Monte Carlo simulations are often used to calculate the system performance but those predictions have statistical uncertainty, the use of noise tolerant optimization algorithms is important. The use of noise tolerant illumination optimization is demonstrated by considering display device designs that extract light using 2D paint patterns as well as 3D textured surfaces. A hybrid optimization approach that combines a mesh feedback optimization with a classical optimizer is demonstrated. Displays with LED sources and cold cathode fluorescent lamps are considered.

Spinodal decomposition regions of InxGa1-xSbyAszN1-y-z, InxGa1-xSbyPzN1-y-z and InxGa1-xAsyPzN1-y-z alloys

NASA Astrophysics Data System (ADS)

Elyukhin, Vyacheslav A.

2017-07-01

Considerable interest in highly mismatched semiconductor alloys as materials for device applications has recently been shown. However, the spinodal instability can be a serious obstacle to their use. Here, the spinodal decomposition regions of dilute nitride InxGa1-xSbyAszN1-y-z, InxGa1-xSbyPzN1-y-z and InxGa1-xAsyPzN1-y-z quinary alloys lattice matched to III-V compounds are studied from 0 °C to 1000 °C. The alloys contain six types of chemical bonds corresponding to the constituent compounds, and rearrangement of atoms changes the bonds between them. Therefore, a size and location of the spinodal decomposition regions depend on the enthalpies of constituent compounds, internal strain energy, coherency strain energy and entropy. Among the considered alloys, InxGa1-xSbyAszN1-y-z lattice matched to InAs, InxGa1-xSbyPzN1-y-z lattice matched to GaP and InP and InxGa1-xAsyPzN1-y-z lattice matched to GaAs and InP are most suitable for device applications.

Ex post manipulation of barriers in InGaAs tunnel injection devices

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

Talalaev, Vadim G.; Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504; Cirlin, George E.

Ex post manipulation of ∼1.1 μm emitting InGaAs/GaAs-based quantum dot–quantum well tunnel injection light emitting devices is demonstrated experimentally. The devices were operated at elevated forward currents until irreversible alterations were observed. As a result, changes in the steady-state optical spectra (electroluminescence, photoluminescence, and photocurrent), in carrier kinetics, in transport properties, and real structure are found. Except for degradation effects, e.g., of larger quantum dots, also restoration/annealing effects such as increased tunnel barriers are observed. The results furnish evidence for a generic degradation mode of nanostructures. We qualitatively interpret the mechanisms involved on both the nanoscopic and the device scales.

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

NASA Astrophysics Data System (ADS)

Zúñiga-Pérez, Jesús; Consonni, Vincent; Lymperakis, Liverios; Kong, Xiang; Trampert, Achim; Fernández-Garrido, Sergio; Brandt, Oliver; Renevier, Hubert; Keller, Stacia; Hestroffer, Karine; Wagner, Markus R.; Reparaz, Juan Sebastián; Akyol, Fatih; Rajan, Siddharth; Rennesson, Stéphanie; Palacios, Tomás; Feuillet, Guy

2016-12-01

The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade.

78 FR 52211 - Certain Electronic Devices Having Placeshifting or Display Replication and Products Containing...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-22

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-878] Certain Electronic Devices Having Placeshifting or Display Replication and Products Containing Same; Commission Determination Not To Review an... States after importation of certain electronic devices having placeshifting or display replication...

On the physical operation and optimization of the p-GaN gate in normally-off GaN HEMT devices

NASA Astrophysics Data System (ADS)

Efthymiou, L.; Longobardi, G.; Camuso, G.; Chien, T.; Chen, M.; Udrea, F.

2017-03-01

In this study, an investigation is undertaken to determine the effect of gate design parameters on the on-state characteristics (threshold voltage and gate turn-on voltage) of pGaN/AlGaN/GaN high electron mobility transistors (HEMTs). Design parameters considered are pGaN doping and gate metal work function. The analysis considers the effects of variations on these parameters using a TCAD model matched with experimental results. A better understanding of the underlying physics governing the operation of these devices is achieved with a view to enable better optimization of such gate designs.

Review—Ultra-Wide-Bandgap AlGaN Power Electronic Devices

DOE PAGES

Kaplar, R. J.; Allerman, A. A.; Armstrong, A. M.; ...

2016-12-20

“Ultra” wide-bandgap semiconductors are an emerging class of materials with bandgaps greater than that of gallium nitride (EG > 3.4 eV) that may ultimately benefit a wide range of applications, including switching power conversion, pulsed power, RF electronics, UV optoelectronics, and quantum information. This paper describes the progress made to date at Sandia National Laboratories to develop one of these materials, aluminum gallium nitride, targeted toward high-power devices. The advantageous material properties of AlGaN are reviewed, questions concerning epitaxial growth and defect physics are covered, and the processing and performance of vertical- and lateral-geometry devices are described. The paper concludesmore » with an assessment of the outlook for AlGaN, including outstanding research opportunities and a brief discussion of other potential applications.« less

Dielectric Coating Thermal Stabilization During GaAs-Based Laser Fabrication for Improved Device Yield

DTIC Science & Technology

2015-11-25

1 Dielectric coating thermal stabilization during GaAs-based laser fabrication for improved device yield 1 Michael K. Connors a, c), Jamal...side contact metal, underlying SiO2 dielectric coating, and semiconductor surface. A thermal-anneal procedure developed for the fabrication of GaAs...slab coupled optical waveguide (SCOW) ridge waveguide devices stabilizes the SiO2 dielectric coating, by means of outgassing and stress reduction

Effect of Dopant Activation on Device Characteristics of InGaN-based Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Lacroce, Nicholas; Liu, Guangyu; Tan, Chee-Keong; Arif, Ronald A.; Lee, Soo Min; Tansu, Nelson

2015-03-01

Achieving high uniformity in growths and device characteristics of InGaN-based light-emitting diodes (LEDs) is important for large scale manufacturing. Dopant activation and maintaining control of variables affecting dopant activation are critical steps in the InGaN-based light emitting diodes (LEDs) fabrication process. In the epitaxy of large scale production LEDs, in-situ post-growth annealing is used for activating the Mg acceptor dopant in the p-AlGaN and p-GaN of the LEDs. However, the annealing temperature varies with respect to position in the reactor chamber, leading to severe uniform dopant activation issue across the devices. Thus, it is important to understand how the temperature gradient and the resulting variance in Mg acceptor activation will alter the device properties. In this work, we examine the effect of varying p-type doping levels in the p-GaN layers and AlGaN electron blocking layer of the GaN LEDs on the optoelectronic properties including the band profile, carrier concentration, current density, output power and quantum efficiency. By understanding the variations and its effect, the identification of the most critical p-type doping layer strategies to address this variation will be clarified.

78 FR 16707 - Certain Digital Photo Frames and Image Display Devices and Components Thereof; Issuance of a...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-18

... Image Display Devices and Components Thereof; Issuance of a Limited Exclusion Order and Cease and Desist... within the United States after importation of certain digital photo frames and image display devices and...: (1) The unlicensed entry of digital photo frames and image display devices and components thereof...

Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures

NASA Astrophysics Data System (ADS)

El-Masry, N. A.; Zavada, J. M.; Reynolds, J. G.; Reynolds, C. L.; Liu, Z.; Bedair, S. M.

2017-08-01

We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A "memory effect" for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon.

Humanization of work circumstances in dialog communication using data display devices, volume 1

NASA Astrophysics Data System (ADS)

Graunke, H.; Julich, H.; Petersen, H. C.; Schaefer, H.; Strupp, K.

1982-11-01

The effects of data display on working places was investigated. Data processing by data display devices is not considered. Important criteria for job contentment is the integration into complex job structures. Corresponding to this principle of organization is team work with a flexible way of labor division which provides the chance and the motivation for a cooperative self controlled working process which give strain caused by data display devices. It is found that in public administration a team with an institutional leadership with primarily social integrative functions is appreciated most.

W-band GaAs camel-cathode Gunn devices produced by MBE

NASA Astrophysics Data System (ADS)

Beall, R. B.; Battersby, S. J.; Grecian, P. J.; Jones, S.; Smith, G.

1989-06-01

The dc and microwave performance of a novel second-harmonic W-band GaAs Gunn device incorporating a camel barrier are reported. Comparison with conventional Gunn devices shows significant improvement in power output and dc to RF conversion efficiency for the new structure. The frequency at which the maximum power is produced is lower for the camel cathode Gunn device, an observation attributed to a reduction in the length of the acceleration zone.

Material quality frontiers of MOVPE grown AlGaAs for minority carrier devices

NASA Astrophysics Data System (ADS)

Heckelmann, S.; Lackner, D.; Dimroth, F.; Bett, A. W.

2017-04-01

In this study, secondary ion mass spectroscopy of oxygen, deep level transient spectroscopy and power dependent relative photoluminescence are compared regarding their ability to resolve differences in AlxGa1-xAs material quality. AlxGa1-xAs samples grown with two different trimethylaluminum sources showing low and high levels of oxygen contamination are compared. As tested in the growth of minority carrier devices, i.e. AlxGa1-xAs solar cells, the two precursors clearly lead to different device characteristics. It is shown that secondary ion mass spectroscopy could not resolve the difference in oxygen concentration, whereas deep level transient spectroscopy and photoluminescence based measurements indicate the influence of the precursor oxygen level on the material quality.

GaN as an interfacial passivation layer: tuning band offset and removing fermi level pinning for III-V MOS devices.

PubMed

Zhang, Zhaofu; Cao, Ruyue; Wang, Changhong; Li, Hao-Bo; Dong, Hong; Wang, Wei-Hua; Lu, Feng; Cheng, Yahui; Xie, Xinjian; Liu, Hui; Cho, Kyeongjae; Wallace, Robert; Wang, Weichao

2015-03-11

The use of an interfacial passivation layer is one important strategy for achieving a high quality interface between high-k and III-V materials integrated into high-mobility metal-oxide-semiconductor field-effect transistor (MOSFET) devices. Here, we propose gallium nitride (GaN) as the interfacial layer between III-V materials and hafnium oxide (HfO2). Utilizing first-principles calculations, we explore the structural and electronic properties of the GaN/HfO2 interface with respect to the interfacial oxygen contents. In the O-rich condition, an O8 interface (eight oxygen atoms at the interface, corresponding to 100% oxygen concentration) displays the most stability. By reducing the interfacial O concentration from 100 to 25%, we find that the interface formation energy increases; when sublayer oxygen vacancies exist, the interface becomes even less stable compared with O8. The band offset is also observed to be highly dependent on the interfacial oxygen concentration. Further analysis of the electronic structure shows that no interface states are present at the O8 interface. These findings indicate that the O8 interface serves as a promising candidate for high quality III-V MOS devices. Moreover, interfacial states are present when such interfacial oxygen is partially removed. The interface states, leading to Fermi level pinning, originate from unsaturated interfacial Ga atoms.

AlGaN/GaN-on-Si monolithic power-switching device with integrated gate current booster

NASA Astrophysics Data System (ADS)

Han, Sang-Woo; Jo, Min-Gi; Kim, Hyungtak; Cho, Chun-Hyung; Cha, Ho-Young

2017-08-01

This study investigates the effects of a monolithic gate current booster integrated with an AlGaN/GaN-on-Si power-switching device. The integrated gate current booster was implemented by a single-stage inverter topology consisting of a recessed normally-off AlGaN/GaN MOS-HFET and a mesa resistor. The monolithically integrated gate current booster in a switching FET eliminated the parasitic elements caused by external interconnection and enabled fast switching operation. The gate charging and discharging currents were boosted by the integrated inverter, which significantly reduced both rise and fall times: the rise time was reduced from 626 to 41.26 ns, while the fall time was reduced from 554 to 42.19 ns by the single-stage inverter. When the packaged monolithic power chip was tested under 1 MHz hard-switching operation with VDD = 200 V, the switching loss was found to have been drastically reduced, from 5.27 to 0.55 W.

XPS/NEXAFS spectroscopic and conductance studies of glycine on AlGaN/GaN transistor devices

NASA Astrophysics Data System (ADS)

Myers, Matthew; Khir, Farah Liyana Muhammad; Home, Michael A.; Mennell, Christopher; Gillbanks, Jeremy; Tadich, Anton; Baker, Murray V.; Nener, Brett D.; Parish, Giacinta

2018-03-01

We report on a study using a combination of XPS/NEXAFS and conductivity measurements to develop a fundamental understanding of how dipolar molecules interact with the heterostructure device surface and affect the device conductivity of AlGaN/GaN heterostructure-based transistors. In such structures, which are increasingly being investigated for chemical and biological sensing, a 2-dimensional electron gas spontaneously forms at the layer interface that is sensitive to the charge characteristics of the exposed surface. Glycine, chosen for this study because it is the simplest of the amino acids and is known to form a zwitterionic configuration when stabilized through intermolecular interactions, was evaporated under ultra-high vacuum conditions onto the device surface and subsequently both XPS/NEXAFS and conductivity measurements were conducted. NEXAFS spectra show a preferential orientation for the Glycine molecules on the surface and evidence for both neutral and zwitterionic species on the surface. In situ conductivity measurements suggest that the negatively charged carboxylate group is closest to the surface. These results are a unique and pivotal contribution to the previous and at times conflicting literature on the zwitterionic nature of Glycine.

Displaying Sensed Tactile Cues with a Fingertip Haptic Device.

PubMed

Pacchierotti, Claudio; Prattichizzo, Domenico; Kuchenbecker, Katherine J

2015-01-01

Telerobotic systems enable humans to explore and manipulate remote environments for applications such as surgery and disaster response, but few such systems provide the operator with cutaneous feedback. This article presents a novel approach to remote cutaneous interaction; our method is compatible with any fingertip tactile sensor and any mechanical tactile display device, and it does not require a position/force or skin deformation model. Instead, it directly maps the sensed stimuli to the best possible input commands for the device's motors using a data set recorded with the tactile sensor inside the device. As a proof of concept, we considered a haptic system composed of a BioTac tactile sensor, in charge of measuring contact deformations, and a custom 3-DoF cutaneous device with a flat contact platform, in charge of applying deformations to the user's fingertip. To validate the proposed approach and discover its inherent tradeoffs, we carried out two remote tactile interaction experiments. The first one evaluated the error between the tactile sensations registered by the BioTac in a remote environment and the sensations created by the cutaneous device for six representative tactile interactions and 27 variations of the display algorithm. The normalized average errors in the best condition were 3.0 percent of the BioTac's full 12-bit scale. The second experiment evaluated human subjects' experiences for the same six remote interactions and eight algorithm variations. The average subjective rating for the best algorithm variation was 8.2 out of 10, where 10 is best.

1000 X Difference Between Current Displays and Capability of Human Visual System: Payoff Potential for Affordable Defense Systems

DTIC Science & Technology

2000-01-01

second tier technologies: digital micromirror devices (DMD); alternating current gas plasma (ACGP); inorganic electroluminescent (EL, TFEL, AMEL... Micromirror Device (DMD) - Alternating Current Gas Plasma (ACGP) - Electroluminescent (EL, TFEL, AMEL) - Vacuum Fluorescent Display (VFD) - Inorganic Light...Instruments Digital Micromirror Device (DMD) Digital Light Processing technology and another, the Qualcomm/Hughes-JVC CRT/Liquid Crystal Light Valve

78 FR 68861 - Certain Navigation Products, Including GPS Devices, Navigation and Display Systems, Radar Systems...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-15

... Devices, Navigation and Display Systems, Radar Systems, Navigational Aids, Mapping Systems and Related... navigation products, including GPS devices, navigation and display systems, radar systems, navigational aids..., radar systems, navigational aids, mapping systems and related software by reason of infringement of one...

Simulation of photons from plasmas for the applications to display devices

NASA Astrophysics Data System (ADS)

Lee, Hae June; Yoon, Hyun Jin; Lee, Jae Koo

2007-07-01

Numerical modeling of the photon transport of the ultraviolet (UV) and the visible lights are presented for plasma based display devices. The transport of UV lights which undergo resonance trapping by ground state atoms is solved by using the Holstein equation. After the UV lights are transformed to visible lights at the phosphor surfaces, the visible lights experience complicated traces inside the cell and finally are emitted toward the viewing window after having some power loss within the cell. A three-dimensional ray trace of the visible lights is calculated with a radiosity model. These simulations for the photons strengthen plasma discharge modeling for the application to display devices.

InGaAlAsPN: A Materials System for Silicon Based Optoelectronics and Heterostructure Device Technologies

NASA Technical Reports Server (NTRS)

Broekaert, T. P. E.; Tang, S.; Wallace, R. M.; Beam, E. A., III; Duncan, W. M.; Kao, Y. -C.; Liu, H. -Y.

1995-01-01

A new material system is proposed for silicon based opto-electronic and heterostructure devices; the silicon lattice matched compositions of the (In,Ga,Al)-(As,P)N 3-5 compounds. In this nitride alloy material system, the bandgap is expected to be direct at the silicon lattice matched compositions with a bandgap range most likely to be in the infrared to visible. At lattice constants ranging between those of silicon carbide and silicon, a wider bandgap range is expected to be available and the high quality material obtained through lattice matching could enable applications such as monolithic color displays, high efficiency multi-junction solar cells, opto-electronic integrated circuits for fiber communications, and the transfer of existing 3-5 technology to silicon.

Updateable 3D Display Using Large Area Photorefractive Polymer Devices

DTIC Science & Technology

2013-04-01

across the thin PR layer. The critical parameters for the buffer layer are: transparent over the range 400nm to 800nm, high dielectric strength , ease of...Holographic 3D Display for Telepresence". Holo- pack.Holo- print 2011, November 9th 2011, (Las-Vegas, NV).  J. Thomas et al., "Recent advances in...AFRL-OSR-VA-TR-2013-0199 Updateable 3D Display Using Large Area Photofractive Polymer Devics Pierre Alexandre Blanche TIPD

Immersive Input Display Device (I2D2) for tactical information viewing

NASA Astrophysics Data System (ADS)

Tremper, David E.; Burnett, Kevin P.; Malloy, Andrew R.; Wert, Robert

2006-05-01

Daylight readability of hand-held displays has been an ongoing issue for both commercial and military applications. In an effort to reduce the effects of ambient light on the readability of military displays, the Naval Research Laboratory (NRL) began investigating and developing advanced hand-held displays. Analysis and research of display technologies with consideration for vulnerability to environmental conditions resulted in the complete design and fabrication of the hand-held Immersive Input Display Device (I2D2) monocular. The I2D2 combines an Organic Light Emitting Diode (OLED) SVGA+ micro-display developed by eMagin Corporation with an optics configuration inside a cylindrical housing. A rubber pressure-eyecup allows view ability only when the eyecup is depressed, eliminating light from both entering and leaving the device. This feature allows the I2D2 to be used during the day, while not allowing ambient light to affect the readability. It simultaneously controls light leakage, effectively eliminating the illumination, and thus preserving the tactical position, of the user in the dark. This paper will examine the characteristics and introduce the design of the I2D2.

76 FR 59737 - In the Matter of Certain Digital Photo Frames and Image Display Devices and Components Thereof...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-27

... Frames and Image Display Devices and Components Thereof; Notice of Institution of Investigation... United States after importation of certain digital photo frames and image display devices and components... certain digital photo frames and image display devices and components thereof that infringe one or more of...

Lighted display devices for producing static or animated visual displays, including animated facial features

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

Heilbron, Valerie J; Clem, Paul G; Cook, Adam Wade

An illuminated display device with a base member with a plurality of cavities therein. Illumination devices illuminate the cavities and emit light through an opening of the cavities in a pattern, and a speaker can emit sounds in synchronization with the pattern. A panel with translucent portions can overly the base member and the cavities. An animated talking character can have an animated mouth cavity complex with multiple predetermined mouth lighting configurations simulative of human utterances. The cavities can be open, or optical waveguide material or positive members can be disposed therein. Reflective material can enhance internal reflectance and lightmore » emission.« less

Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition.

PubMed

Nguyen, H Q; Yu, H W; Luc, Q H; Tang, Y Z; Phan, V T H; Hsu, C H; Chang, E Y; Tseng, Y C

2014-12-05

Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique's precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼10(6) cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

77 FR 31876 - Certain Consumer Electronics and Display Devices and Products Containing Same Determination Not...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-30

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-836] Certain Consumer Electronics and Display Devices and Products Containing Same Determination Not To Review Initial Determination To Amend... electronics and display devices and products containing the same by reason of infringement of U.S. Patent Nos...

Radiation Characterization of Commercial GaN Devices

NASA Technical Reports Server (NTRS)

Harris, Richard D.; Scheick, Leif Z.; Hoffman, James P.; Thrivikraman, Tushar; Jenabi, Masud; Gim, Yonggyu; Miyahira, Tetsuo

2011-01-01

Radiative feedback from primordial protostars and final mass of the first star Commercially available devices fabricated from GaN are beginning to appear from a number of different suppliers. Based on previous materials and prototype device studies, it is expected that these commercial devices will be quite tolerant to the types of radiation encountered in space. This expectation needs to be verified and the study described herein was undertaken for that purpose. All of the parts discussed in this report are readily available commercially. The parts chosen for study are all targeted for RF applications. Three different studies were performed: 1) a preliminary DDD/TID test of a variety of part types was performed by irradiating with 50 MeV protons, 2) a detailed DDD/TID study of one particular part type was performed by irradiating with 50 MeV protons, and 3) a SEB/SEGR test was performed on a variety of part types by irradiating with heavy ions. No significant degradation was observed in the tests performed in this study.

808nm high-power high-efficiency GaAsP/GaInP laser bars

NASA Astrophysics Data System (ADS)

Wang, Ye; Yang, Ye; Qin, Li; Wang, Chao; Yao, Di; Liu, Yun; Wang, Lijun

2008-11-01

808nm high power diode lasers, which is rapidly maturing technology technically and commercially since the introduction in 1999 of complete kilowatt-scale diode laser systems, have important applications in the fields of industry and pumping solid-state lasers (DPSSL). High power and high power conversion efficiency are extremely important in diode lasers, and they could lead to new applications where space, weight and electrical power are critical. High efficiency devices generate less waste heat, which means less strain on the cooling system and more tolerance to thermal conductivity variation, a lower junction temperature and longer lifetimes. Diode lasers with Al-free materials have superior power conversion efficiency compared with conventional AlGaAs/GaAs devices because of their lower differential series resistance and higher thermal conductivity. 808nm GaAsP/GaInP broad-waveguide emitting diode laser bars with 1mm cavity length have been fabricated. The peak power can reach to 100.9W at 106.5A at quasicontinuous wave operation (200μs, 1000Hz). The maximum power conversion efficiency is 57.38%. Based on these high power laser bars, we fabricate a 1x3 arrays, the maximum power is 64.3W in continuous wave mode when the current is 25.0A. And the threshold current is 5.9A, the slope efficiency is 3.37 W/A.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1989-01-01

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

Analysis of 2D Transport and Performance Characteristics for Lateral Power Devices Based on AlGaN Alloys

DOE PAGES

Coltrin, Michael E.; Baca, Albert G.; Kaplar, Robert J.

2017-10-26

In this paper, predicted lateral power device performance as a function of alloy composition is characterized by a standard lateral device figure-of-merit (LFOM) that depends on mobility, critical electric field, and sheet carrier density. The paper presents calculations of AlGaN electron mobility in lateral devices such as HEMTs across the entire alloy composition range. Alloy scattering and optical polar phonon scattering are the dominant mechanisms limiting carrier mobility. Due to the significant degradation of mobility from alloy scattering, at room temperature Al fractions greater than about 85% are required for improved LFOM relative to GaN using a conservative sheet chargemore » density of 1 × 10 13 cm –2. However, at higher temperatures at which AlGaN power devices are anticipated to operate, this “breakeven” composition decreases to about 65% at 500 K, for example. For high-frequency applications, the Johnson figure-of-merit (JFOM) is the relevant metric to compare potential device performance across materials platforms. At room temperature, the JFOM for AlGaN alloys is predicted to surpass that of GaN for Al fractions greater than about 40%.« less

Analysis of 2D Transport and Performance Characteristics for Lateral Power Devices Based on AlGaN Alloys

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

Coltrin, Michael E.; Baca, Albert G.; Kaplar, Robert J.

In this paper, predicted lateral power device performance as a function of alloy composition is characterized by a standard lateral device figure-of-merit (LFOM) that depends on mobility, critical electric field, and sheet carrier density. The paper presents calculations of AlGaN electron mobility in lateral devices such as HEMTs across the entire alloy composition range. Alloy scattering and optical polar phonon scattering are the dominant mechanisms limiting carrier mobility. Due to the significant degradation of mobility from alloy scattering, at room temperature Al fractions greater than about 85% are required for improved LFOM relative to GaN using a conservative sheet chargemore » density of 1 × 10 13 cm –2. However, at higher temperatures at which AlGaN power devices are anticipated to operate, this “breakeven” composition decreases to about 65% at 500 K, for example. For high-frequency applications, the Johnson figure-of-merit (JFOM) is the relevant metric to compare potential device performance across materials platforms. At room temperature, the JFOM for AlGaN alloys is predicted to surpass that of GaN for Al fractions greater than about 40%.« less

GaAs integrated circuits and heterojunction devices

NASA Astrophysics Data System (ADS)

Fowlis, Colin

1986-06-01

The state of the art of GaAs technology in the U.S. as it applies to digital and analog integrated circuits is examined. In a market projection, it is noted that whereas analog ICs now largely dominate the market, in 1994 they will amount to only 39 percent vs. 57 percent for digital ICs. The military segment of the market will remain the largest (42 percent in 1994 vs. 70 percent today). ICs using depletion-mode-only FETs can be constructed in various forms, the closest to production being BFL or buffered FET logic. Schottky diode FET logic - a lower power approach - can reach higher complexities and strong efforts are being made in this direction. Enhancement type devices appear essential to reach LSI and VLSI complexity, but process control is still very difficult; strong efforts are under way, both in the U.S. and in Japan. Heterojunction devices appear very promising, although structures are fairly complex, and special fabrication techniques, such as molecular beam epitaxy and MOCVD, are necessary. High-electron-mobility-transistor (HEMT) devices show significant performance advantages over MESFETs at low temperatures. Initial results of heterojunction bipolar transistor devices show promise for high speed A/D converter applications.

77 FR 14422 - Certain Consumer Electronics and Display Devices and Products Containing Same; Notice of Receipt...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-09

... INTERNATIONAL TRADE COMMISSION [DN 2882] Certain Consumer Electronics and Display Devices and... the U.S. International Trade Commission has received a complaint entitled Certain Consumer Electronics... importation of certain consumer electronics and display devices and products containing same. The complaint...

Extreme Radiation Hardness and Space Qualification of AlGaN Optoelectronic Devices

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

Sun, Ke-Xun; Balakrishnan, Kathik; Hultgren, Eric

2010-09-21

Unprecedented radiation hardness and environment robustness are required in the new generation of high energy density physics (HEDP) experiments and deep space exploration. National Ignition Facility (NIF) break-even shots will have a neutron yield of 1015 or higher. The Europa Jupiter System Mission (EJSM) mission instruments will be irradiated with a total fluence of 1012 protons/cm2 during the space journey. In addition, large temperature variations and mechanical shocks are expected in these applications under extreme conditions. Hefty radiation and thermal shields are required for Si and GaAs based electronics and optoelectronics devices. However, for direct illumination and imaging applications, shieldingmore » is not a viable option. It is an urgent task to search for new semiconductor technologies and to develop radiation hard and environmentally robust optoelectronic devices. We will report on our latest systematic experimental studies on radiation hardness and space qualifications of AlGaN optoelectronic devices: Deep UV Light Emitting Diodes (DUV LEDs) and solarblind UV Photodiodes (PDs). For custom designed AlGaN DUV LEDs with a central emission wavelength of 255 nm, we have demonstrated its extreme radiation hardness up to 2x1012 protons/cm2 with 63.9 MeV proton beams. We have demonstrated an operation lifetime of over 26,000 hours in a nitrogen rich environment, and 23,000 hours of operation in vacuum without significant power drop and spectral shift. The DUV LEDs with multiple packaging styles have passed stringent space qualifications with 14 g random vibrations, and 21 cycles of 100K temperature cycles. The driving voltage, current, emission spectra and optical power (V-I-P) operation characteristics exhibited no significant changes after the space environmental tests. The DUV LEDs will be used for photoelectric charge management in space flights. For custom designed AlGaN UV photodiodes with a central response wavelength of 255 nm, we have

76 FR 38417 - In the Matter of Certain Multimedia Display and Navigation Devices and Systems, Components...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-30

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-694] In the Matter of Certain Multimedia Display and Navigation Devices and Systems, Components Thereof, and Products Containing Same; Notice of... importation of certain multimedia display and navigation devices and systems, components thereof, and products...

76 FR 25707 - In The Matter of Certain Multimedia Display and Navigation Devices and Systems, Components...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-05

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-694] In The Matter of Certain Multimedia Display and Navigation Devices and Systems, Components Thereof, and Products Containing Same; Notice of... multimedia display and navigation devices and systems, components thereof, and products containing same by...

Multijunction InGaAs thermophotovoltaic devices

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

Fatemi, N.S.; Jenkins, P.P.; Weizer, V.G.

1998-12-31

A monolithic interconnected module (MIM) structure has been developed for thermophotovoltaic (TPV) applications. The MIM consists of many individual InGaAs cells series-connected on a single semi-insulating (S.I.) InP substrate. An infrared (IR) back surface reflector (BSR), placed on the rear surface of the substrate, returns the unused portion of the TPV radiator output spectrum back to the radiator for recuperation, thereby providing for high system efficiencies. MIMs were fabricated with an active area of 0.9 {times} 1 cm, and with 15 cells monolithically connected in series. Both lattice-matched and lattice-mismatched InGaAs/InP devices were fabricated, with bandgaps of 0.74 and 0.55more » eV, respectively. The 0.74 eV MIMs demonstrated an open-circuit voltage (Voc) of 6.16 V and a fill factor of 74.2% at a short-circuit current (Jsc) of 0.84 A/cm{sup 2}, under flashlamp testing. The 0.55 eV MIMs demonstrated a Voc of 4.85 V and a fill factor of 57.8% at a Jsc of 3.87 A/cm{sup 2}. Electrical performance results for these MIMs are presented.« less

Characterization of vertical GaN p-n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

NASA Astrophysics Data System (ADS)

Kizilyalli, I. C.; Aktas, O.

2015-12-01

field-effect transistors with BV = 1000 V and drain currents of 4 A are fabricated and characterized over the same temperature range. It is demonstrated that vertical GaN devices (diodes and transistors) utilizing p-n junctions are suitable for most practical applications including automotive ones (210 K < T < 423 K). While devices are functional at cryogenic temperatures (77 K) there may be some limitations to their performance due the freeze-out of Mg acceptors.

(Al)GaInP/GaAs Tandem Solar Cells for Power Conversion at Elevated Temperature and High Concentration

DOE PAGES

Perl, Emmett E.; Simon, John; Friedman, Daniel J.; ...

2018-01-12

We demonstrate dual-junction (Al)GaInP/GaAs solar cells designed for operation at 400 degrees C and 1000x concentration. For the top junction, we compare (Al)GaInP solar cells with room-temperature bandgaps ranging from 1.9 to 2.0 eV. At 400 degrees C, we find that ~1.9 eV GaInP solar cells have a higher open-circuit voltage and a lower sheet resistance than higher bandgap (Al)GaInP solar cells, giving them a clear advantage in a tandem configuration. Dual-junction GaInP/GaAs solar cells are fabricated, and we show temperature-dependent external quantum efficiency, illuminated current-voltage, and concentrator measurements from 25 degrees C to 400 degrees C. We measure amore » power conversion efficiency of 16.4% +/- 1% at 400 degrees C and 345 suns for the best dual-junction cell, and discuss multiple pathways to improve the performance further. After undergoing a 200 h soak at 400 degrees C, the dual-junction device shows a relative loss in efficiency of only ~1%.« less

(Al)GaInP/GaAs Tandem Solar Cells for Power Conversion at Elevated Temperature and High Concentration

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

Perl, Emmett E.; Simon, John; Friedman, Daniel J.

We demonstrate dual-junction (Al)GaInP/GaAs solar cells designed for operation at 400 degrees C and 1000x concentration. For the top junction, we compare (Al)GaInP solar cells with room-temperature bandgaps ranging from 1.9 to 2.0 eV. At 400 degrees C, we find that ~1.9 eV GaInP solar cells have a higher open-circuit voltage and a lower sheet resistance than higher bandgap (Al)GaInP solar cells, giving them a clear advantage in a tandem configuration. Dual-junction GaInP/GaAs solar cells are fabricated, and we show temperature-dependent external quantum efficiency, illuminated current-voltage, and concentrator measurements from 25 degrees C to 400 degrees C. We measure amore » power conversion efficiency of 16.4% +/- 1% at 400 degrees C and 345 suns for the best dual-junction cell, and discuss multiple pathways to improve the performance further. After undergoing a 200 h soak at 400 degrees C, the dual-junction device shows a relative loss in efficiency of only ~1%.« less

Rare-metal-free high-performance Ga-Sn-O thin film transistor

NASA Astrophysics Data System (ADS)

Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

2017-03-01

Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

Rare-metal-free high-performance Ga-Sn-O thin film transistor

PubMed Central

Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

2017-01-01

Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds. PMID:28290547

Rare-metal-free high-performance Ga-Sn-O thin film transistor.

PubMed

Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

2017-03-14

Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm 2 /Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

Numerical simulation and characterization of trapping noise in InGaP-GaAs heterojunctions devices at high injection

NASA Astrophysics Data System (ADS)

Nallatamby, Jean-Christophe; Abdelhadi, Khaled; Jacquet, Jean-Claude; Prigent, Michel; Floriot, Didier; Delage, Sylvain; Obregon, Juan

2013-03-01

Commercially available simulators present considerable advantages in performing accurate DC, AC and transient simulations of semiconductor devices, including many fundamental and parasitic effects which are not generally taken into account in house-made simulators. Nevertheless, while the TCAD simulators of the public domain we have tested give accurate results for the simulation of diffusion noise, none of the tested simulators perform trap-assisted GR noise accurately. In order to overcome the aforementioned problem we propose a robust solution to accurately simulate GR noise due to traps. It is based on numerical processing of the output data of one of the simulators available in the public-domain, namely SENTAURUS (from Synopsys). We have linked together, through a dedicated Data Access Component (DAC), the deterministic output data available from SENTAURUS and a powerful, customizable post-processing tool developed on the mathematical SCILAB software package. Thus, robust simulations of GR noise in semiconductor devices can be performed by using GR Langevin sources associated to the scalar Green functions responses of the device. Our method takes advantage of the accuracy of the deterministic simulations of electronic devices obtained with SENTAURUS. A Comparison between 2-D simulations and measurements of low frequency noise on InGaP-GaAs heterojunctions, at low as well as high injection levels, demonstrates the validity of the proposed simulation tool.

Extraction of physical Schottky parameters using the Lambert function in Ni/AlGaN/GaN HEMT devices with defined conduction phenomena

NASA Astrophysics Data System (ADS)

Latry, O.; Divay, A.; Fadil, D.; Dherbécourt, P.

2017-01-01

Electrical characterization analyses are proposed in this work using the Lambert function on Schottky junctions in GaN wide band gap semiconductor devices for extraction of physical parameters. The Lambert function is used to give an explicit expression of the current in the Schottky junction. This function is applied with defined conduction phenomena, whereas other work presented arbitrary (or undefined) conduction mechanisms in such parameters’ extractions. Based upon AlGaN/GaN HEMT structures, extractions of parameters are undergone in order to provide physical characteristics. This work highlights a new expression of current with defined conduction phenomena in order to quantify the physical properties of Schottky contacts in AlGaN/GaN HEMT transistors. Project supported by the French Department of Defense (DGA).

Lack of quantum confinement in Ga2O3 nanolayers

NASA Astrophysics Data System (ADS)

Peelaers, Hartwin; Van de Walle, Chris G.

2017-08-01

β -Ga2Ox3 is a wide-band-gap semiconductor with promising applications in transparent electronics and in power devices. β -Ga2O3 has monoclinic crystal symmetry and does not display a layered structured characteristic of 2D materials in the bulk; nevertheless, monolayer-thin Ga2O3 layers can be created. We used first-principles techniques to investigate the structural and electronic properties of these nanolayers. Surprisingly, freestanding films do not exhibit any signs of quantum confinement and exhibit the same electronic structure as bulk material. A detailed examination reveals that this can be attributed to the presence of states that are strongly confined near the surface. When the Ga2O3 layers are embedded in a wider band-gap material such as Al2O3 , the expected effects of quantum confinement can be observed. The effective mass of electrons in all the nanolayers is small, indicating promising device applications.

Medical applications of near-eye display devices: an exploratory study.

PubMed

Vorraber, Wolfgang; Voessner, Siegfried; Stark, Gerhard; Neubacher, Dietmar; DeMello, Steven; Bair, Aaron

2014-12-01

Near-eye display devices (such as Google Glass) may improve the efficiency and effectiveness of clinical care by giving clinicians information (such as the patient's vital signs) continuously within their field of vision during various procedures. We describe the use of Glass during a radiological intervention in three patients. Other possible applications (including tele-mentoring and the supervision of trainees) are discussed and a classification proposed. An app was developed to facilitate the use of Glass, so vital physical signs (pulse and blood pressure) could be projected on the near-eye display, via an intranet to protect sensitive data. The device was then used during radiological interventions (percutaneous transluminal angioplasty) in three patients, and assessed by the interventionalists who were interviewed before and after each procedure. The interventionalists reported that Google Glass improved concentration on the task in hand by reducing head and neck movements (which would be needed to view several remote monitors). However, heat generation by the device and low battery capacity are shortcomings for which solutions must be developed, and data protection is mandatory. Google Glass may have a number of clinical applications and can quicken interventions where vital signs or other visual data need to be monitored by the operator. Copyright © 2014 Surgical Associates Ltd. All rights reserved.

Three-Dimensional Hetero-Integration of Faceted GaN on Si Pillars for Efficient Light Energy Conversion Devices.

PubMed

Kim, Dong Rip; Lee, Chi Hwan; Cho, In Sun; Jang, Hanmin; Jeon, Min Soo; Zheng, Xiaolin

2017-07-25

An important pathway for cost-effective light energy conversion devices, such as solar cells and light emitting diodes, is to integrate III-V (e.g., GaN) materials on Si substrates. Such integration first necessitates growth of high crystalline III-V materials on Si, which has been the focus of many studies. However, the integration also requires that the final III-V/Si structure has a high light energy conversion efficiency. To accomplish these twin goals, we use single-crystalline microsized Si pillars as a seed layer to first grow faceted Si structures, which are then used for the heteroepitaxial growth of faceted GaN films. These faceted GaN films on Si have high crystallinity, and their threading dislocation density is similar to that of GaN grown on sapphire. In addition, the final faceted GaN/Si structure has great light absorption and extraction characteristics, leading to improved performance for GaN-on-Si light energy conversion devices.

Atypical self-activation of Ga dopant for Ge nanowire devices.

PubMed

Zeiner, Clemens; Lugstein, Alois; Burchhart, Thomas; Pongratz, Peter; Connell, Justin G; Lauhon, Lincoln J; Bertagnolli, Emmerich

2011-08-10

In this Letter we report the atypical self-activation of gallium (Ga) implanted by focused ion beam (FIB) into germanium nanowires (Ge-NWs). By FIB implantation of 30 keV Ga(+) ions at room temperature, the Ge-NW conductivity increases up to 3 orders of magnitude with increasing ion fluence. Cu(3)Ge heterostructures were formed by diffusion to ensure well-defined contacts to the NW and enable two point I/V measurements. Additional four point measurements prove that the conductivity enhancement emerges from the modification of the wires themselves and not from contact property modifications. The Ga distribution in the implanted Ge-NWs was measured using atom probe tomography. For high ion fluences, and beginning amorphization of the NWs, the conductivity decreases exponentially. Temperature dependent conductivity measurements show strong evidence for an in situ doping of the Ge-NWs without any further annealing. Finally the feasibility of improving the device performance of top-gated Ge-NW MOSFETs by FIB implantation was shown.

The Fundamentals of Using the Digital Micromirror Device (DMD(TM)) for Projection Display

NASA Technical Reports Server (NTRS)

Yoder, Lars A.

1995-01-01

Developed by Texas Instruments (TI) the digital micromirror device (DMD(tm)) is a quickly emerging and highly useful micro-electro-mechanical structures (MEMS) device. Using standard semiconductor fabrication technology, the DMD's simplicity in concept and design will provide advantageous solutions for many different applications. At the rudimentary level, the DMD is a precision, semiconductor light switch. In the initial commercial development of DMD technology, TI has concentrated on projection display and hardcopy. This paper will focus on how the DMD is used for projection display. Other application areas are being explored and evaluated to find appropriate and beneficial uses for the DMD.

Switching between attractive and repulsive Coulomb-interaction-mediated drag in an ambipolar GaAs/AlGaAs bilayer device

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

Zheng, B.; Croxall, A. F.; Waldie, J., E-mail: jw353@cam.ac.uk

2016-02-08

We present measurements of Coulomb drag in an ambipolar GaAs/AlGaAs double quantum well structure that can be configured as both an electron-hole bilayer and a hole-hole bilayer, with an insulating barrier of only 10 nm between the two quantum wells. Coulomb drag resistivity is a direct measure of the strength of interlayer particle-particle interactions. We explore the strongly interacting regime of low carrier densities (2D interaction parameter r{sub s} up to 14). Our ambipolar device design allows a comparison between the effects of the attractive electron-hole and repulsive hole-hole interactions and also shows the effects of the different effective masses ofmore » electrons and holes in GaAs.« less

Formulation of electroclinic, ferroelectric and antiferroelectric liquid crystal mixtures suitable for display devices

NASA Astrophysics Data System (ADS)

Debnath, Asim; Goswami, Debarghya; Mandal, Pradip Kumar

2018-04-01

Most of the liquid crystal display (LCD) devices starting from simplest wrist watches or calculators to complex laptops or flat TV sets are based on nematics. Although a tremendous improvement in the quality of display as well as reduction of manufacturing cost has taken place over the years, there are many issues which the LC industry is trying hard to address. Ferroelectric liquid crystals (FLC) are of current interest in the LCD industry since among various other advantages FLC based displays have micro-second order switching compared to milli-second order switching in nematic based displays. To meet the market demand much effort has been made to optimize the physical parameters of FLCs, such as temperature range, spontaneous polarization (PS), helical pitch (p), switching time (τ), tilt angle (θ) and rotational viscosity (γ). Multicomponent mixtures are, therefore, formulated to optimize all the required properties for practical applications since no single FLC compound can satisfy the above requirements. To the best of our knowledge electroclinic, ferroelectric and antiferroelectric liquid crystal mixtures have been formulated first time by any Indian group which have properties suitable for FLC based display devices and at par with mixtures used in the industry.

A power device material of corundum-structured α-Ga2O3 fabricated by MIST EPITAXY® technique

NASA Astrophysics Data System (ADS)

Kaneko, Kentaro; Fujita, Shizuo; Hitora, Toshimi

2018-02-01

Corundum-structured oxides have been attracting much attention as next-generation power device materials. A corundum-structured α-Ga2O3 successfully demonstrated power device operations of Schottky barrier diodes (SBDs) with the lowest on-resistance of 0.1 mΩ cm2. The SBDs as a mounting device of TO220 also showed low switching-loss properties with a capacitance of 130 pF. Moreover, the thermal resistance was 13.9 °C/W, which is comparable to that of the SiC TO220 device (12.5 °C/W). On the other hand, corundum-structured α-(Rh,Ga)2O3 showed p-type conductivity, which was confirmed by Hall effect measurements. The Hall coefficient, carrier density, and mobility were 8.22 cm3/C, 7.6 × 1017/cm3, and 1.0 cm2 V-1 s-1, respectively. These values were acceptable for the p-type layer of pn diodes based on α-Ga2O3.

DISPLAY3D. A Graphics Preprocessor for CHIEF

DTIC Science & Technology

1990-12-27

graphics devices, the user may write a graphics program th.,.t can read DISPLAY3D output files, or use one of the commercial plotting packages...COMMON/NBPRTC/IRHSPT, NARSPT, NPTBLK FRQPT COMMON/NBPRTS/SYMTPT CHARACTER*3 SYMTPT DIMENSION CC(10), TRNS(3), IELTS (8,300) real xl(1000) ,yl(leee...C Prompt the user for filename. C--- ------------------------------------------------------- WRITE (6,1) ’Enter filename used in CID or

A review of Ga2O3 materials, processing, and devices

NASA Astrophysics Data System (ADS)

Pearton, S. J.; Yang, Jiancheng; Cary, Patrick H.; Ren, F.; Kim, Jihyun; Tadjer, Marko J.; Mastro, Michael A.

2018-03-01

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (ɛ) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Uniformity of dc and rf performance of MBE-grown AlGaN/GaN HEMTS on HVPE-grown buffers

NASA Astrophysics Data System (ADS)

Gillespie, J. K.; Fitch, R. C.; Moser, N.; Jenkins, T.; Sewell, J.; Via, D.; Crespo, A.; Dabiran, A. M.; Chow, P. P.; Osinsky, A.; Mastro, M. A.; Tsvetkov, D.; Soukhoveev, V.; Usikov, A.; Dmitriev, V.; Luo, B.; Pearton, S. J.; Ren, F.

2003-10-01

AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) on 2 in. diameter GaN buffer layers grown by hydride vapor epitaxy (HVPE) on sapphire substrates. HEMTs with 1 μm gate length displayed excellent dc and rf performance uniformity with up to 258 separate devices measured for each parameter. The drain-source saturation current was 561 mA with a standard deviation of 1.9% over the 2 in. diameter, with a corresponding transconductance of 118 ± 3.9 mS/mm. The threshold voltage was -5.3 ± 0.07 V. The rf performance uniformity was equally good, with an fT of 8.6 ± 0.8 GHz and fmax of 12.8 ± 2.5 GHz. The results show the excellent uniformity of the MBE technique for producing AlGaN/GaN HEMTs and also the ability of HVPE to provide high quality buffers at low cost.

Native defects in GaN: a hybrid functional study

NASA Astrophysics Data System (ADS)

Diallo, Ibrahima Castillo; Demchenko, Denis

Intrinsic defects play an important role in the performance of GaN-based devices. We present hybrid density functional calculations of the electronic and possible optical properties of interstitial N (Ni-Ni) , N antisite (NGa) , interstitial Ga (Gai) , Ga antisite (GaN) , Ga vacancy (VGa) , N vacancy (VN) and Ga-N divacancies (VGaVN) in GaN. Our results show that the vacancies display relatively low formation energies in certain samples, whereas antisites and interstitials are energetically less favorable. However, interstitials can be created by electron irradiation. For instance, in 2.5 MeV electron-irradiated GaN samples, a strong correlation between the frequently observed photoluminescence (PL) band centered around 0.85 eV accompanied with a rich phonon sideband of ~0.88 eV and the theoretical optical behavior of interstitial Ga is discussed. N vacancies are found to likely contribute to the experimentally obtained green luminescence band (GL2) peaking at 2.24 eV in high-resistivity undoped and Mg-doped GaN. National Science Foundation (DMR-1410125) and the Thomas F. and Kate Miller Jeffress Memorial Trust.

28 percent efficient GaAs concentrator solar cells

NASA Technical Reports Server (NTRS)

Macmillan, H. F.; Hamaker, H. C.; Kaminar, N. R.; Kuryla, M. S.; Ladle Ristow, M.

1988-01-01

AlGaAs/GaAs heteroface solar concentrator cells which exhibit efficiencies in excess of 27 percent at high solar concentrations (over 400 suns, AM1.5D, 100 mW/sq cm) have been fabricated with both n/p and p/n configurations. The best n/p cell achieved an efficiency of 28.1 percent around 400 suns, and the best p/n cell achieved an efficiency of 27.5 percent around 1000 suns. The high performance of these GaAs concentrator cells compared to earlier high-efficiency cells was due to improved control of the metal-organic chemical vapor deposition growth conditions and improved cell fabrication procedures (gridline definition and edge passivation). The design parameters of the solar cell structures and optimized grid pattern were determined with a realistic computer modeling program. An evaluation of the device characteristics and a discussion of future GaAs concentrator cell development are presented.

Degradation Mechanisms for GaN and GaAs High Speed Transistors

PubMed Central

Cheney, David J.; Douglas, Erica A.; Liu, Lu; Lo, Chien-Fong; Gila, Brent P.; Ren, Fan; Pearton, Stephen J.

2012-01-01

We present a review of reliability issues in AlGaN/GaN and AlGaAs/GaAs high electron mobility transistors (HEMTs) as well as Heterojunction Bipolar Transistors (HBTs) in the AlGaAs/GaAs materials systems. Because of the complex nature and multi-faceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. We review the electric field driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plate), and the effect of device fabrication processes for both DC and RF stress conditions. We summarize the degradation mechanisms that limit the lifetime of these devices. A variety of contact and surface degradation mechanisms have been reported, but differ in the two device technologies: For HEMTs, the layers are thin and relatively lightly doped compared to HBT structures and there is a metal Schottky gate that is directly on the semiconductor. By contrast, the HBT relies on pn junctions for current modulation and has only Ohmic contacts. This leads to different degradation mechanisms for the two types of devices.

MEASUREMENT OF PHONON TRANSPORT IN GaN-ON-SiC AND GaN-ON-DIAMOND HIGH ELECTRON MOBILITY TRANSISTOR (HEMT) DEVICES

DTIC Science & Technology

2017-10-16

DARPA) or the U.S. Government. Report contains color. 14. ABSTRACT The objective of this project is to experimentally study the transient non ...the Metal Thin Film in TDTR ........................................ 14 4.3 Experimental Observation of the Frequency Filtering Effect...scale of the device layers and the high density of interfaces, non -diffusive heat conduction plays a critical role in thermal transport of GaN devices

Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices

NASA Astrophysics Data System (ADS)

Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.

MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.

Effect of device package on optical, spectral, and thermal properties of InGaN/GaN near-ultraviolet lateral light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Soo Hyun; Guan, Xiang-Yu; Jeon, Soo-Kun; Yu, Jae Su

2017-09-01

We investigated the package effect on the temperature-dependent optical and spectral characteristics of InGaN/GaN near-ultraviolet (NUV) lateral light-emitting diodes (LLEDs) on the metal heatsink (MH) and package (PKG) in the injection current range of 0 - 500 mA at 298 and 358 K. For the NUV LLEDs on the MH, the device characteristics reflected directly its chip performance. For the NUV LLEDs on the PKG, the rapidly varied spectral shift as well as the reduced device efficiency was observed due to the increased number of layers with relatively low thermal conductivities. The junction temperature ( T j ) and thermal resistance of the NUV LLEDs on the PKG were also significantly increased compared to the NUV LLEDs on the MH. The three-dimensional heat transfer simulations for both the devices were carried out to obtain the temperature distributions by finite element method. The theoretically calculated T j values showed a good agreement with the experimentally measured T j values.

Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-spreading layer.

PubMed

Zhang, Zi-Hui; Tan, Swee Tiam; Liu, Wei; Ju, Zhengang; Zheng, Ke; Kyaw, Zabu; Ji, Yun; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

2013-02-25

This work reports both experimental and theoretical studies on the InGaN/GaN light-emitting diodes (LEDs) with optical output power and external quantum efficiency (EQE) levels substantially enhanced by incorporating p-GaN/n-GaN/p-GaN/n-GaN/p-GaN (PNPNP-GaN) current spreading layers in p-GaN. Each thin n-GaN layer sandwiched in the PNPNP-GaN structure is completely depleted due to the built-in electric field in the PNPNP-GaN junctions, and the ionized donors in these n-GaN layers serve as the hole spreaders. As a result, the electrical performance of the proposed device is improved and the optical output power and EQE are enhanced.

Self-Supporting GaN Nanowires/Graphite Paper: Novel High-Performance Flexible Supercapacitor Electrodes.

PubMed

Wang, Shouzhi; Sun, Changlong; Shao, Yongliang; Wu, Yongzhong; Zhang, Lei; Hao, Xiaopeng

2017-02-01

Flexible supercapacitors have attracted great interest as energy storage devices because of their promise in applications such as wearable and smart electronic devices. Herein, a novel flexible supercapacitor electrode based on gallium nitride nanowire (GaN NW)/graphite paper (GP) nanocomposites is reported. The outstanding electrical conductivities of the GaN NW (6.36 × 10 2 S m -1 ) and GP (7.5 × 10 4 S m -1 ) deliver a synergistically enhanced electrochemical performance that cannot be achieved by either of the components alone. The composite electrode exhibits excellent specific capacitance (237 mF cm -2 at 0.1 mA cm -2 ) and outstanding cycling performance (98% capacitance retention after 10 000 cycles). The flexible symmetric supercapacitor also manifests high energy and power densities (0.30 mW h cm -3 and 1000 mW cm -3 ). These findings demonstrate that the GaN/GP composite electrode has significant potential as a candidate for the flexible energy storage devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-sensitivity two-terminal magnetoresistance devices using InGaAs/AlGaAs two-dimensional channel on GaAs substrate

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

Wu, Di-Cheng; Pan, You-Wei; Lin, Shih-Wei

2016-04-25

We demonstrate experimentally the two-terminal magnetic sensors exhibiting an extraordinary magneto-resistance effect by using an InGaAs quantum well channel with a metal-shunting structure. A high magneto-resistance of 17.3% and a sensitivity of 488.1 Ω/T have been obtained at 1 T and room temperature with our geometrical design. The two-contact configuration and the high-mobility electron transistor-compatible epitaxy structure make the devices promising for high-sensitivity magnetic sensing integration and applications.

Study on the photoresponse of amorphous In-Ga-Zn-O and zinc oxynitride semiconductor devices by the extraction of sub-gap-state distribution and device simulation.

PubMed

Jang, Jun Tae; Park, Jozeph; Ahn, Byung Du; Kim, Dong Myong; Choi, Sung-Jin; Kim, Hyun-Suk; Kim, Dae Hwan

2015-07-22

Persistent photoconduction (PPC) is a phenomenon that limits the application of oxide semiconductor thin-film transistors (TFTs) in optical sensor-embedded displays. In the present work, a study on zinc oxynitride (ZnON) semiconductor TFTs based on the combination of experimental results and device simulation is presented. Devices incorporating ZnON semiconductors exhibit negligible PPC effects compared with amorphous In-Ga-Zn-O (a-IGZO) TFTs, and the difference between the two types of materials are examined by monochromatic photonic C-V spectroscopy (MPCVS). The latter method allows the estimation of the density of subgap states in the semiconductor, which may account for the different behavior of ZnON and IGZO materials with respect to illumination and the associated PPC. In the case of a-IGZO TFTs, the oxygen flow rate during the sputter deposition of a-IGZO is found to influence the amount of PPC. Small oxygen flow rates result in pronounced PPC, and large densities of valence band tail (VBT) states are observed in the corresponding devices. This implies a dependence of PPC on the amount of oxygen vacancies (VO). On the other hand, ZnON has a smaller bandgap than a-IGZO and contains a smaller density of VBT states over the entire range of its bandgap energy. Here, the concept of activation energy window (AEW) is introduced to explain the occurrence of PPC effects by photoinduced electron doping, which is likely to be associated with the formation of peroxides in the semiconductor. The analytical methodology presented in this report accounts well for the reduction of PPC in ZnON TFTs, and provides a quantitative tool for the systematic development of phototransistors for optical sensor-embedded interactive displays.

Interface trap of p-type gate integrated AlGaN/GaN heterostructure field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Kyu Sang

2017-09-01

In this work, the impact of trap states at the p-(Al)GaN/AlGaN interface has been investigated for the normally-off mode p-(Al)GaN/AlGaN/GaN heterostructure field-effect transistors (HFETs) by means of frequency dependent conductance. From the current-voltage (I-V) measurement, it was found that the p-AlGaN gate integrated device has higher drain current and lower gate leakage current compared to the p-GaN gate integrated device. We obtained the interface trap density and the characteristic time constant for the p-type gate integrated HFETs under the forward gate voltage of up to 6 V. As a result, the interface trap density (characteristic time constant) of the p-GaN gate device was lower (longer) than that of the p-AlGaN. Furthermore, it was analyzed that the trap state energy level of the p-GaN gate device was located at the shallow level relative to the p-AlGaN gate device, which accounts for different gate leakage current of each devices.

Method and device for producing a tactile display using an electrorheological fluid

NASA Technical Reports Server (NTRS)

Garner, H. Douglas (Inventor)

1996-01-01

A tactile display device utilizes an electrorheological fluid to activate a plurality of tactile dots. A voltage is selectively produced uniformly across an electrorheological fluid flowing between a common ground electrode and a plurality of conductive dot electrodes, thereby producing an increase in the fluid's viscosity to the extent that fluid flow between the two electrodes is restricted. The flow restriction produces a build-up of electrorheological fluid in a corresponding dot actuator chamber. The resulting pressure increase in the chamber displaces an elastic diaphragm fixed to a display surface to form a lump which can be perceived by the reader as one dot in a Braille character cell. A flow regulation system provides a continually pressurized flow system and provides for free flow of the electrorheological fluid through the plurality of dot actuator chambers when they are not activated. The device is adaptable to printed circuit techniques and can simultaneously display tactile dots representative of a full page of Braille characters stored on a medium such as a tape cassette or to display tactile dots representative of non-Braille data appearing on a computer monitor or contained on another data storage medium. In an alternate embodiment, the elastic diaphragm drives a plurality of spring-loaded pins provided with positive stops to maintain consistent displacements of the pins in both their actuated and nonactuated positions.

Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications

DOE PAGES

Mitchell, Brandon; Timmerman, D.; Poplawsky, Jonathan D.; ...

2016-01-04

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions thatmore » were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. Furthermore, these findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.« less

Low-voltage cross-sectional EBIC for characterisation of GaN-based light emitting devices.

PubMed

Moldovan, Grigore; Kazemian, Payam; Edwards, Paul R; Ong, Vincent K S; Kurniawan, Oka; Humphreys, Colin J

2007-01-01

Electron beam induced current (EBIC) characterisation can provide detailed information on the influence of crystalline defects on the diffusion and recombination of minority carriers in semiconductors. New developments are required for GaN light emitting devices, which need a cross-sectional approach to provide access to their complex multi-layered structures. A sample preparation approach based on low-voltage Ar ion milling is proposed here and shown to produce a flat cross-section with very limited surface recombination, which enables low-voltage high resolution EBIC characterisation. Dark defects are observed in EBIC images and correlation with cathodoluminescence images identify them as threading dislocations. Emphasis is placed on one-dimensional quantification which is used to show that junction delineation with very good spatial resolution can be achieved, revealing significant roughening of this GaN p-n junction. Furthermore, longer minority carrier diffusion lengths along the c-axis are found at dislocation sites, in both p-GaN and the multi-quantum well (MQW) region. This is attributed to gettering of point defects at threading dislocations in p-GaN and higher escape rate from quantum wells at dislocation sites in the MQW region, respectively. These developments show considerable promise for the use of low-voltage cross-sectional EBIC in the characterisation of point and extended defects in GaN-based devices and it is suggested that this technique will be particularly useful for degradation analysis.

Tunable surface acoustic wave device based on acoustoelectric interaction in ZnO/GaN heterostructures

NASA Astrophysics Data System (ADS)

Li, Rui; Reyes, Pavel I.; Ragavendiran, Sowmya; Shen, H.; Lu, Yicheng

2015-08-01

A tunable surface acoustic wave (SAW) device is developed on a multilayer structure which consists of an n-type semiconductor ZnO layer and a Ni-doped piezoelectric ZnO layer deposited on a GaN/c-Al2O3 substrate. The unique acoustic dispersion relationship between ZnO and GaN generates the multi-mode SAW response in this structure, facilitating high frequency operation. A dc bias voltage is applied to a Ti/Au gate layer deposited on the path of SAW delay line to modulate the electrical conductivity for tuning the acoustic velocity. For devices operating at 1.25 GHz, a maximum SAW velocity change of 0.9% is achieved, equivalent to the frequency change of 11.2 MHz. This voltage-controlled frequency tuning device has potential applications in resettable sensors, adaptive signal processing, and secure wireless communication.

Above room temperature operation of InGaAs/AlGaAs/GaAs quantum cascade lasers

NASA Astrophysics Data System (ADS)

Pierścińska, D.; Gutowski, P.; Hałdaś, G.; Kolek, A.; Sankowska, I.; Grzonka, J.; Mizera, J.; Pierściński, K.; Bugajski, M.

2018-03-01

In this work we report on the performance of mid-infrared quantum cascade lasers (QCLs) based on strained InGaAs/AlGaAs grown by molecular beam epitaxy on GaAs substrate. Structures were grown with indium content from 1% to 6% in GaAs quantum wells (QW) and 45% of Al in AlGaAs barrier layers. The design results in strained heterostructure, however, no strain relaxation was observed as documented by x-ray diffraction measurements up to ∼3% of In content in QWs. The investigation of heterostructures and devices was performed, including structural measurements and electrooptical characterization of devices. Devices fabricated from epi wafers with 2.64% of In exhibited performance largely improved over GaAs/AlGaAs QCLs. Roughly two times reduction of the threshold current density was observed at lasing wavelength ∼9.45 μm. The lasers operated in pulsed mode up to T = 50 °C with characteristic temperature T 0 = 115 K. The decrease of the threshold current density has been mainly attributed to the reduction of interface roughness scattering and the increase of activation energy for the escape of carriers from the upper laser level to the 3D continuum. Further increase of In content in QWs resulted in the deterioration of device parameters.

Quantitative strain and compositional studies of InxGa1-xAs Epilayer in a GaAs-based pHEMT device structure by TEM techniques.

PubMed

Sridhara Rao, Duggi V; Sankarasubramanian, Ramachandran; Muraleedharan, Kuttanellore; Mehrtens, Thorsten; Rosenauer, Andreas; Banerjee, Dipankar

2014-08-01

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the In x Ga1-x As channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the In x Ga1-x As layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the In x Ga1-x As channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

77 FR 21584 - Certain Consumer Electronics and Display Devices and Products Containing Same; Institution of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-10

... INTERNATIONAL TRADE COMMISSION [Inv. No. 337-TA-836] Certain Consumer Electronics and Display... electronics and display devices and products containing same by reason of infringement of certain claims of U... importation, or the sale within the United States after importation of certain consumer electronics and...

Seamless tiled display system

NASA Technical Reports Server (NTRS)

Dubin, Matthew B. (Inventor); Larson, Brent D. (Inventor); Kolosowsky, Aleksandra (Inventor)

2006-01-01

A modular and scalable seamless tiled display apparatus includes multiple display devices, a screen, and multiple lens assemblies. Each display device is subdivided into multiple sections, and each section is configured to display a sectional image. One of the lens assemblies is optically coupled to each of the sections of each of the display devices to project the sectional image displayed on that section onto the screen. The multiple lens assemblies are configured to merge the projected sectional images to form a single tiled image. The projected sectional images may be merged on the screen by magnifying and shifting the images in an appropriate manner. The magnification and shifting of these images eliminates any visual effect on the tiled display that may result from dead-band regions defined between each pair of adjacent sections on each display device, and due to gaps between multiple display devices.

On the AlGaInP-bulk and AlGaInP/GaAs-superlattice confinement effects for heterostructure-emitter bipolar transistors

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

Tsai, Jung-Hui, E-mail: jhtsai@nknucc.nknu.edu.tw

2015-02-09

The confinement effect and electrical characteristics of heterostructure-emitter bipolar transistors with an AlGaInP bulk-confinement layer and an AlGaInP/GaAs superlattice-confinement layer are first demonstrated and compared by experimentally results. In the two devices, the relatively large valence band discontinuity at AlGaInP/GaAs heterojunction provides excellent confinement effect for holes to enhance current gain. As to the AlGaInP/GaAs superlattice-confinement device, part of thermionic-emission electrons will be trapped in the GaAs quantum wells of the superlattice. This will result in lower collector current and current gain as compared with the bulk-confinement device. Nevertheless, the superlattice-confinement device exhibits a larger current-gain cutoff frequency, which canmore » be attributed that the tunneling behavior is included in the carrier transportation and transporting time across the emitter region could be substantially reduced.« less

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

NASA Astrophysics Data System (ADS)

Le, Son Phuong; Nguyen, Duong Dai; Suzuki, Toshi-kazu

2018-01-01

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

Amorphous InGaMgO Ultraviolet Photo-TFT with Ultrahigh Photosensitivity and Extremely Large Responsivity

PubMed Central

Zhang, Yiyu; Qian, Ling-Xuan; Wu, Zehan; Liu, Xingzhao

2017-01-01

Recently, amorphous InGaZnO ultraviolet photo thin-film transistors have exhibited great potential for application in future display technologies. Nevertheless, the transmittance of amorphous InGaZnO (~80%) is still not high enough, resulting in the relatively large sacrifice of aperture ratio for each sensor pixel. In this work, the ultraviolet photo thin-film transistor based on amorphous InGaMgO, which processes a larger bandgap and higher transmission compared to amorphous InGaZnO, was proposed and investigated. Furthermore, the effects of post-deposition annealing in oxygen on both the material and ultraviolet detection characteristics of amorphous InGaMgO were also comprehensively studied. It was found that oxygen post-deposition annealing can effectively reduce oxygen vacancies, leading to an optimized device performance, including lower dark current, higher sensitivity, and larger responsivity. We attributed it to the combined effect of the reduction in donor states and recombination centers, both of which are related to oxygen vacancies. As a result, the 240-min annealed device exhibited the lowest dark current of 1.7 × 10−10 A, the highest photosensitivity of 3.9 × 106, and the largest responsivity of 1.5 × 104 A/W. Therefore, our findings have revealed that amorphous InGaMgO photo thin-film transistors are a very promising alternative for UV detection, especially for application in touch-free interactive displays. PMID:28772529

Amorphous InGaMgO Ultraviolet Photo-TFT with Ultrahigh Photosensitivity and Extremely Large Responsivity.

PubMed

Zhang, Yiyu; Qian, Ling-Xuan; Wu, Zehan; Liu, Xingzhao

2017-02-13

Recently, amorphous InGaZnO ultraviolet photo thin-film transistors have exhibited great potential for application in future display technologies. Nevertheless, the transmittance of amorphous InGaZnO (~80%) is still not high enough, resulting in the relatively large sacrifice of aperture ratio for each sensor pixel. In this work, the ultraviolet photo thin-film transistor based on amorphous InGaMgO, which processes a larger bandgap and higher transmission compared to amorphous InGaZnO, was proposed and investigated. Furthermore, the effects of post-deposition annealing in oxygen on both the material and ultraviolet detection characteristics of amorphous InGaMgO were also comprehensively studied. It was found that oxygen post-deposition annealing can effectively reduce oxygen vacancies, leading to an optimized device performance, including lower dark current, higher sensitivity, and larger responsivity. We attributed it to the combined effect of the reduction in donor states and recombination centers, both of which are related to oxygen vacancies. As a result, the 240-min annealed device exhibited the lowest dark current of 1.7 × 10 -10 A, the highest photosensitivity of 3.9 × 10⁶, and the largest responsivity of 1.5 × 10⁴ A/W. Therefore, our findings have revealed that amorphous InGaMgO photo thin-film transistors are a very promising alternative for UV detection, especially for application in touch-free interactive displays.

GaAs Surface Passivation for Device Applications.

DTIC Science & Technology

1981-12-01

Ga203.’" . QI. a) / b) x 2.5 •• 24 21 18 As3d a) b) x 2. / 0 II 2 46 43 40 BINDING ENERGY (eV) Fig. 3 XPS spectra from a Ga2O3 covered GaAs surface of Ga...wU 24 21 Gas 18 SAs3d As2O3 ) .. 46 43 40 BINDING ENERGY (e) Fig. 4 XPS spectra from a AsJ03- Ga2O3 covered GaAs surface of Ga 3d (upper panel) and As

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Design of integrated eye tracker-display device for head mounted systems

NASA Astrophysics Data System (ADS)

David, Y.; Apter, B.; Thirer, N.; Baal-Zedaka, I.; Efron, U.

2009-08-01

We propose an Eye Tracker/Display system, based on a novel, dual function device termed ETD, which allows sharing the optical paths of the Eye tracker and the display and on-chip processing. The proposed ETD design is based on a CMOS chip combining a Liquid-Crystal-on-Silicon (LCoS) micro-display technology with near infrared (NIR) Active Pixel Sensor imager. The ET operation allows capturing the Near IR (NIR) light, back-reflected from the eye's retina. The retinal image is then used for the detection of the current direction of eye's gaze. The design of the eye tracking imager is based on the "deep p-well" pixel technology, providing low crosstalk while shielding the active pixel circuitry, which serves the imaging and the display drivers, from the photo charges generated in the substrate. The use of the ETD in the HMD Design enables a very compact design suitable for Smart Goggle applications. A preliminary optical, electronic and digital design of the goggle and its associated ETD chip and digital control, are presented.

High-Efficiency Visible Transmitting Polarizations Devices Based on the GaN Metasurface.

PubMed

Guo, Zhongyi; Xu, Haisheng; Guo, Kai; Shen, Fei; Zhou, Hongping; Zhou, Qingfeng; Gao, Jun; Yin, Zhiping

2018-05-15

Metasurfaces are capable of tailoring the amplitude, phase, and polarization of incident light to design various polarization devices. Here, we propose a metasurface based on the novel dielectric material gallium nitride (GaN) to realize high-efficiency modulation for both of the orthogonal linear polarizations simultaneously in the visible range. Both modulated transmitted phases of the orthogonal linear polarizations can almost span the whole 2π range by tailoring geometric sizes of the GaN nanobricks, while maintaining high values of transmission (almost all over 90%). At the wavelength of 530 nm, we designed and realized the beam splitter and the focusing lenses successfully. To further prove that our proposed method is suitable for arbitrary orthogonal linear polarization, we also designed a three-dimensional (3D) metalens that can simultaneously focus the X -, Y -, 45°, and 135° linear polarizations on spatially symmetric positions, which can be applied to the linear polarization measurement. Our work provides a possible method to achieve high-efficiency multifunctional optical devices in visible light by extending the modulating dimensions.

Electronic and optical properties of GaSb:N from first principles

NASA Astrophysics Data System (ADS)

Jadaun, Priyamvada; Nair, Hari; Lordi, Vincenzo; Bank, Seth; Banerjee, Sanjay

2014-03-01

We present an ab-initio study of dilute nitride III-Vs, focusing on dilute nitride GaSb (GaSb:N). GaSb:N displays promise towards realization of optoelectronic devices accessing the mid-infrared wavelength regime. Theoretical and experimental results on its electronic and optical properties are however few. To address this, we present a first principles, density functional theory study using the hybrid HSE06 exchange-correlation functional of GaSb doped with 1.6% nitrogen. We conduct a comparative study on GaAs:N, also with 1.6% nitrogen mole fraction, and find that GaSb:N has a smaller band gap and displays more band gap bowing than GaAs:N. In addition we examine the orbital character of the bands, finding the lowest conduction band to be quasi-delocalized, with a large N-3s contribution. At high concentrations, the N atoms interact via the host matrix, forming a dispersive band of their own which governs optoelectronic properties and dominates band gap bowing. While this band drives the optical and electronic properties of GaSb:N, its physics is not captured by traditional models for dilute-nitrides. We thus propose that a complete theory of dilute-nitrides should incorporate orbital character examination, especially at high N concentrations. Texas Advanced Computing Center (TACC), U.S. Department of Energy, Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

High-resolution depth profile of the InGaP-on-GaAs heterointerface by FE-AES and its relationship to device properties

NASA Astrophysics Data System (ADS)

Ichikawa, O.; Fukuhara, N.; Hata, M.; Nakano, T.; Sugiyama, M.; Shimogaki, Y.; Nakano, Y.

2007-01-01

At InGaP-on-GaAs heterointerface, transition layer is formed during metalorganic vapor phase epitaxy (MOVPE) growth that can affect device properties. Many studies of this transition layer have been done but the characterization methods used are not direct measures of the atomic structure at the heterointerface. In this study, we investigated the abruptness and thickness of the InGaP-on-GaAs transition layers by field-emission Auger electron spectroscopy, by which a depth profile with a resolution of abruptness of 30 Å or below can be obtained. The group V switching position relative to that of In goes deeper into the GaAs with increasing PH 3 supply, suggesting an initial, quick replacement of As atoms with P atoms followed by a slow P diffusion into the bulk GaAs. Changes of abruptness of the As or P profiles at the heterointerface with varying PH 3 supply on the GaAs surface are not observed. Furthermore, we evaluated the effect of the GaAsP-like transition layers on the turn-on voltage of an InGaP emitter HBT. A linear relationship is shown between the shift of the group V switching position and the HBT turn-on voltage, which is consistent with the assumption that current flow decreases at the transition layer. Calculated difference of conduction band energy between InGaP and the transition layer is 0.15 eV for the sample with ordered InGaP and 0.04 eV for disordered InGaP, is consistent with the difference of the band gap energies between ordered and disordered InGaP. Calculated P compositions are 0.52 and 0.35, respectively.

On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for InGaN/GaN light-emitting diodes.

PubMed

Kyaw, Zabu; Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ju, Zhen Gang; Zhang, Xue Liang; Ji, Yun; Hasanov, Namig; Zhu, Binbin; Lu, Shunpeng; Zhang, Yiping; Sun, Xiao Wei; Demir, Hilmi Volkan

2014-01-13

N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n- GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.

Observation of low voltage driven green emission from erbium doped Ga{sub 2}O{sub 3} light-emitting devices

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

Chen, Zhengwei; Wang, Xu; Zhang, Fabi

Erbium doped Ga{sub 2}O{sub 3} thin films were deposited on Si substrate by pulsed laser deposition method. Bright green emission (∼548 nm) can be observed by naked eye from Ga{sub 2}O{sub 3}:Er/Si light-emitting devices (LEDs). The driven voltage of this LEDs is 6.2 V which is lower than that of ZnO:Er/Si or GaN:Er/Si devices. Since the wide bandgap of Ga{sub 2}O{sub 3} contain more defect-related level which will enhance the effects of recombination between electrons in the defect-related level and the holes in the valence band, resulting in the improvement of the energy transfer to Er ions. We believe that this workmore » paves the way for the development of Si-based green LEDs by using wide bandgap Ga{sub 2}O{sub 3} as the host materials for Er{sup 3+} ions.« less

GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

PubMed

Hashida, Ryohei; Sasaki, Takashi; Hane, Kazuhiro

2018-03-20

Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510 nm in thickness, 1000 nm in width, and a clad of 240 nm in thickness. A GaN crystalline layer of 1000 nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300 nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7  dB/mm around a wavelength of 1.55 μm. The microring radii ranged from 30 to 60 μm, where the measured free-spectral ranges varied from 2.58 to 5.30 nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.

Pilot Designed Aircraft Displays in General Aviation: An Exploratory Study and Analysis

NASA Astrophysics Data System (ADS)

Conaway, Cody R.

From 2001-2011, the General Aviation (GA) fatal accident rate remained unchanged (Duquette & Dorr, 2014) with an overall stagnant accident rate between 2004 and 2013. The leading cause, loss of control in flight (NTSB, 2015b & 2015c) due to pilot inability to recognize approach to stall/spin conditions (NTSB, 2015b & 2016b). In 2013, there were 1,224 GA accidents in the U.S., accounting for 94% of all U.S. aviation accidents and 90% of all U.S. aviation fatalities that year (NTSB, 2015c). Aviation entails multiple challenges for pilots related to task management, procedural errors, perceptual distortions, and cognitive discrepancies. While machine errors in airplanes have continued to decrease over the years, human error still has not (NTSB, 2013). A preliminary analysis of a PC-based, Garmin G1000 flight deck was conducted with 3 professional pilots. Analyses revealed increased task load, opportunities for distraction, confusing perceptual ques, and hindered cognitive performance. Complex usage problems were deeply ingrained in the functionality of the system, forcing pilots to use fallible work arounds, add unnecessary steps, and memorize knob turns or button pushes. Modern computing now has the potential to free GA cockpit designs from knobs, soft keys, or limited display options. Dynamic digital displays might include changes in instrumentation or menu structuring depending on the phase of flight. Airspeed indicators could increase in size to become more salient during landing, simultaneously highlighting pitch angle on Attitude Indicators and automatically decluttering unnecessary information for landing. Likewise, Angle-of-Attack indicators demonstrate a great safety and performance advantage for pilots (Duquette & Dorr, 2014; NTSB, 2015b & 2016b), an instrument typically found in military platforms and now the Icon A5, light-sport aircraft (Icon, 2016). How does the design of pilots' environment---the cockpit---further influence their efficiency and

Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

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

Bolat, Sami, E-mail: bolat@ee.bilkent.edu.tr; Tekcan, Burak; Ozgit-Akgun, Cagla

2015-01-15

Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal–semiconductor–metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N{sub 2}/H{sub 2} PA-ALD based GaN channels aremore » observed to have improved stability and transfer characteristics with respect to NH{sub 3} PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N{sub 2}:H{sub 2} ambient.« less

Using Mobile Devices to Display, Overlay, and Animate Geophysical Data and Imagery

NASA Astrophysics Data System (ADS)

Batzli, S.; Parker, D.

2011-12-01

A major challenge in mobile-device map application development is to offer rich content and features with simple and intuitive controls and fast performance. Our goal is to bring visualization, animation, and notifications of near real-time weather and earth observation information derived from satellite and sensor data to mobile devices. Our robust back-end processing infrastructure can deliver content in the form of images, shapes, standard descriptive formats (eg. KML, JSON) or raw data to a variety of desktop software, browsers, and mobile devices on demand. We have developed custom interfaces for low-bandwidth browsers (including mobile phones) and high-feature browsers (including smartphones), as well as native applications for Android and iOS devices. Mobile devices offer time- and location-awareness and persistent data connections, allowing us to tailor timely notifications and displays to the user's geographic and time context. This presentation includes a live demo of how our mobile apps deliver animation of standard and custom data products in an interactive map interface.

Aqueous synthesis of zinc oxide films for GaN optoelectronic devices

NASA Astrophysics Data System (ADS)

Reading, Arthur H.

GaN-based LEDs have generally made use of ITO transparent contacts as current-spreading layers for uniform current injection. However, the high raw material and processing costs of ITO layers have generated interest in potentially cheaper alternatives. In this work, zinc oxide transparent layers were fabricated by a low-cost, low-temperature aqueous epitaxial growth method at 90°C for use as transparent contacts to GaN LEDs on c-plane sapphire, and on semipolar bulk GaN substrates. Low-voltage operation was achieved for c-plane devices, with voltages below 3.8V for 1mm2 broad-area LEDs at a current density of 30A/cm 2. Blue-green LEDs on 202¯1¯-plane GaN also showed low voltage operation below 3.5V at 30A/cm2. Ohmic contact resistivity of 1:8 x 10-2Ocm2 was measured for films on (202¯1) p-GaN templates. Ga-doped films had electrical conductivities as high as 660S/cm after annealing at 300°C. Optical characterization revealed optical absorption coefficients in the 50--200cm -1 range for visible light, allowing thick films with sheet resistances below 10O/□ to be grown while minimizing absorption of the emitted light. Accurate and reproducible etch-free patterning of the ZnO films was achieved using templated growths with SiOx hard masks. A roughening method is described which was found to increase peak LED efficiencies by 13% on c-plane patterned sapphire (PSS) substrates. In addition, ZnO films were successfully employed as laser-cladding layers for blue (202¯1) lasers, with a threshold current density of 8.8kA/cm 2.

Atomic Layer Deposition of Gallium Oxide Films as Gate Dielectrics in AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors

NASA Astrophysics Data System (ADS)

Shih, Huan-Yu; Chu, Fu-Chuan; Das, Atanu; Lee, Chia-Yu; Chen, Ming-Jang; Lin, Ray-Ming

2016-04-01

In this study, films of gallium oxide (Ga2O3) were prepared through remote plasma atomic layer deposition (RP-ALD) using triethylgallium and oxygen plasma. The chemical composition and optical properties of the Ga2O3 thin films were investigated; the saturation growth displayed a linear dependence with respect to the number of ALD cycles. These uniform ALD films exhibited excellent uniformity and smooth Ga2O3-GaN interfaces. An ALD Ga2O3 film was then used as the gate dielectric and surface passivation layer in a metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT), which exhibited device performance superior to that of a corresponding conventional Schottky gate HEMT. Under similar bias conditions, the gate leakage currents of the MOS-HEMT were two orders of magnitude lower than those of the conventional HEMT, with the power-added efficiency enhanced by up to 9 %. The subthreshold swing and effective interfacial state density of the MOS-HEMT were 78 mV decade-1 and 3.62 × 1011 eV-1 cm-2, respectively. The direct-current and radio-frequency performances of the MOS-HEMT device were greater than those of the conventional HEMT. In addition, the flicker noise of the MOS-HEMT was lower than that of the conventional HEMT.

AlGaInP/GaAs tandem solar cells for power conversion at 400°C and high concentration

NASA Astrophysics Data System (ADS)

Steiner, Myles A.; Perl, Emmett E.; Simon, John; Friedman, Daniel J.; Jain, Nikhil; Sharps, Paul; McPheeters, Claiborne; Lee, Minjoo Larry

2017-09-01

We demonstrate dual junction (Al)GaInP/GaAs solar cells that are designed to operate at 400°C and 1000X concentration in a hybrid photovoltaic-solar thermal concentrator system. The cells have a front metallization and anti-reflection coating that are stable under 400°C operation. We show how the cell performance degrades with increasing aluminum compositions in the top cell. Our best cell is a GaInP/GaAs tandem that demonstrated 15±1% efficiency at 400°C over a concentration range of 300-1000 suns, with several pathways to improved performance.

Comparison of alloy disorder scatterings in Ga- and N-polar AlGaN/GaN heterostructures

NASA Astrophysics Data System (ADS)

Kang, He; Li, Hui-Jie; Yang, Shao-Yan; Zhang, Wei; Zhu, Ming; Liu, Li; Li, Nan

2018-01-01

The two-dimensional electron gas (2DEG) mobilities limited by alloy disorder (AD) scattering in both Ga- and N-polar AlGaN/GaN heterostructures are investigated. It was found that the AD scattering limited electron mobility in N-polar heterostructures is on the order of 103-104 cm2/Vs, which is comparable to the optical phonon scattering at room-temperature. In comparison, the AD scattering in Ga-polar samples is much less important. Moreover, the electron mobility decreases with the 2DEG density in the Ga-polar device but shows a reverse trend in the N-polar counterpart. This is found to be caused by the rather different electric field distributions in Ga- and N-polar AlGaN/GaN heterostructures. In addition, we find that an AlN interlayer can effectively reduce the alloy scattering, mainly due to the large band offset between AlN and GaN. The calculated mobilities have been compared with the experiment results and good agreements are found. We believe that our results are important for the design of AlGaN/GaN heterostructure-based devices, especially the N-polar ones.

Ultra-Thin, Triple-Bandgap GaInP/GaAs/GaInAs Monolithic Tandem Solar Cells

NASA Technical Reports Server (NTRS)

Wanlass, M. W.; Ahrenkiel, S. P.; Albin, D. S.; Carapella, J. J.; Duda, A.; Emery, K.; Geisz, J. F.; Jones, K.; Kurtz, Sarah; Moriarty, T.;

Illuminant-adaptive color reproduction for mobile display

NASA Astrophysics Data System (ADS)

Kim, Jong-Man; Park, Kee-Hyon; Kwon, Oh-Seol; Cho, Yang-Ho; Ha, Yeong-Ho

2006-01-01

This paper proposes an illuminant-adaptive reproduction method using light adaptation and flare conditions for a mobile display. Mobile displays, such as PDAs and cellular phones, are viewed under various lighting conditions. In particular, images displayed in daylight are perceived as quite dark due to the light adaptation of the human visual system, as the luminance of a mobile display is considerably lower than that of an outdoor environment. In addition, flare phenomena decrease the color gamut of a mobile display by increasing the luminance of dark areas and de-saturating the chroma. Therefore, this paper presents an enhancement method composed of lightness enhancement and chroma compensation. First, the ambient light intensity is measured using a lux-sensor, then the flare is calculated based on the reflection ratio of the display device and the ambient light intensity. The relative cone response is nonlinear to the input luminance. This is also changed by the ambient light intensity. Thus, to improve the perceived image, the displayed luminance is enhanced by lightness linearization. In this paper, the image's luminance is transformed by linearization of the response to the input luminance according to the ambient light intensity. Next, the displayed image is compensated according to the physically reduced chroma, resulting from flare phenomena. The reduced chroma value is calculated according to the flare for each intensity. The chroma compensation method to maintain the original image's chroma is applied differently for each hue plane, as the flare affects each hue plane differently. At this time, the enhanced chroma also considers the gamut boundary. Based on experimental observations, the outer luminance-intensity generally ranges from 1,000 lux to 30,000 lux. Thus, in the case of an outdoor environment, i.e. greater than 1,000 lux, this study presents a color reproduction method based on an inverse cone response curve and flare condition. Consequently

Multibias and thermal behavior of microwave GaN and GaAs based HEMTs

NASA Astrophysics Data System (ADS)

Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

2016-12-01

Multibias and thermal characterizations on 0.25 μm × (2 × 100) μm AlGaN/GaN/SiC HEMT and 0.5 μm × (2 × 100) μm AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance RTH of 7.1, 8.2 and 9.4 °C mm/W for the GaN device was estimated at 25, 75 and 150 °C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage VT, Schottky barrier height ϕb, sheet charge densities of two dimensional electron gas ns, and capacitance under the gate Cg are exactly opposite in the two devices; whereas the knee voltage Vk, on resistance Ron, and series resistance Rseries are shows similar trend. The multi-bias and thermal behavior of the output current Ids, output conductance gds, transconductance gm, cut-off frequency ft, maximum frequency fmax, effective velocity of electron, veff and field dependent mobility, μ demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications.

On the design of GaN vertical MESFETs on commercial LED sapphire wafers

NASA Astrophysics Data System (ADS)

Atalla, Mahmoud R. M.; Noor Elahi, Asim M.; Mo, Chen; Jiang, Zhenyu; Liu, Jie; Ashok, S.; Xu, Jian

2016-12-01

Design of GaN-based vertical metal-semiconductor field-effect transistors (MESFETs) on commercial light-emitting-diode (LED) epi-wafers has been proposed and proof of principle devices have been fabricated. In order to better understand the IV curves, these devices have been simulated using the charge transport model. It was found that shrinking the drain pillar size would significantly help in reaching cut-off at much lower gate bias even at high carrier concentration of unintentionally doped GaN and considerable leakage current caused by the Schottky barrier lowering. The realization of these vertical MESFETs on LED wafers would allow their chip-level integration. This would open a way to many intelligent lighting applications like on-chip current regulator and signal regulation/communication in display technology.

Large Arrays of Microcavity Plasma Devices for Active Displays and Backlighting

NASA Astrophysics Data System (ADS)

Eden, J. Gary; Park, Sung-Jin; Ostrom, Nels P.; Chen, Kuo-Feng; Kim, Kwang Soo

2005-09-01

Developments of the past several years in the technology of microcavity plasma devices having characteristic dimensions of 10-100 µm suggests their applicability to the next generation of active and passive displays. Two examples of device structures that are well suited for economically manufactured arrays of large active area are presented. Arrays as large as 500 x 500 (2.5 ṡ 105) pixels of Si inverted pyramid microplasma devices, with emitting apertures of 50 x 50 µm2 and designed for AC or bipolar excitation, have been designed and operated successfully in the rare gases at pressures up to and beyond one atmosphere. Multilayer Al/nanostructured Al2O3 microplasma devices having 100-300 µm diam. cylindrical microcavities are robust and operate in the abnormal glow mode for rare gas or Ar/2-5% N2 mixture pressures of 500-700 torr. Grown by a wet chemical process, the nanoporous Al2O3 dielectric yields a lightweight, flexible structure that produces intense visible or ultraviolet emission when driven by sinusoidal AC or bipolar voltage waveforms.

Design and characterization of GaN p-i-n diodes for betavoltaic devices

NASA Astrophysics Data System (ADS)

Khan, Muhammad R.; Smith, Joshua R.; Tompkins, Randy P.; Kelley, Stephen; Litz, Marc; Russo, John; Leathersich, Jeff; Shahedipour-Sandvik, Fatemeh (Shadi); Jones, Kenneth A.; Iliadis, Agis

2017-10-01

The performance of gallium nitride (GaN) p-i-n diodes were investigated for use as a betavoltaic device. Dark IV measurements showed a turn on-voltage of approximately 3.2 V, specific-on-resistance of 15.1 mΩ cm2 and a reverse leakage current of -0.14 mA/cm2 at -10 V. A clear photo-response was observed when IV curves were measured under a light source at a wavelength of 310 nm (4.0 eV). In addition, GaN p-i-n diodes were tested under an electron-beam in order to simulate common beta radiation sources ranging from that of 3H (5.6 keV average) to 63Ni (17 keV average). From this data, we estimated output powers of 53 nW and 750 nW with overall efficiencies of 0.96% and 4.4% for our device at incident electron energies of 5.6 keV and 17 keV corresponding to 3H and 63Ni beta sources respectively.

Ka-band Ga-As FET noise receiver/device development

NASA Technical Reports Server (NTRS)

Schellenberg, J. M.; Feng, M.; Hackett, L. H.; Watkins, E. T.; Yamasaki, H.

1982-01-01

The development of technology for a 30 GHz low noise receiver utilizing GaAs FET devices exclusively is discussed. This program required single and dual-gate FET devices, low noise FET amplifiers, dual-gate FET mixers, and FET oscillators operating at Ka-band frequencies. A 0.25 micrometer gate FET device, developed with a minimum noise figure of 3.3 dB at 29 GHz and an associated gain of 7.4 dB, was used to fabricate a 3-stage amplifier with a minimum noise figure and associated gain of 4.4 dB and 17 dB, respectively. The 1-dB gain bandwidth of this amplifier extended from below 26.5 GHz to 30.5 GHz. A dual-gate mixer with a 2 dB conversion loss and a minimum noise figure of 10 dB at 29 GHz as well as a dielectric resonator stabilized FET oscillator at 25 GHz for the receiver L0. From these components, a hybrid microwave integrated circuit receiver was constructed which demonstrates a minimum single-side band noise figure of 4.6 dB at 29 GHz with a conversion gain of 17 dB. The output power at the 1-dB gain compression point was -5 dBm.

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

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

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Laser-induced local activation of Mg-doped GaN with a high lateral resolution for high power vertical devices

NASA Astrophysics Data System (ADS)

Kurose, Noriko; Matsumoto, Kota; Yamada, Fumihiko; Roffi, Teuku Muhammad; Kamiya, Itaru; Iwata, Naotaka; Aoyagi, Yoshinobu

2018-01-01

A method for laser-induced local p-type activation of an as-grown Mg-doped GaN sample with a high lateral resolution is developed for realizing high power vertical devices for the first time. As-grown Mg-doped GaN is converted to p-type GaN in a confined local area. The transition from an insulating to a p-type area is realized to take place within about 1-2 μm fine resolution. The results show that the technique can be applied in fabricating the devices such as vertical field effect transistors, vertical bipolar transistors and vertical Schottkey diode so on with a current confinement region using a p-type carrier-blocking layer formed by this technique.

The application of autostereoscopic display in smart home system based on mobile devices

NASA Astrophysics Data System (ADS)

Zhang, Yongjun; Ling, Zhi

2015-03-01

Smart home is a system to control home devices which are more and more popular in our daily life. Mobile intelligent terminals based on smart homes have been developed, make remote controlling and monitoring possible with smartphones or tablets. On the other hand, 3D stereo display technology developed rapidly in recent years. Therefore, a iPad-based smart home system adopts autostereoscopic display as the control interface is proposed to improve the userfriendliness of using experiences. In consideration of iPad's limited hardware capabilities, we introduced a 3D image synthesizing method based on parallel processing with Graphic Processing Unit (GPU) implemented it with OpenGL ES Application Programming Interface (API) library on IOS platforms for real-time autostereoscopic displaying. Compared to the traditional smart home system, the proposed system applied autostereoscopic display into smart home system's control interface enhanced the reality, user-friendliness and visual comfort of interface.

Ultralow-voltage-drop GaN/InGaN/GaN tunnel junctions with 12% indium content

NASA Astrophysics Data System (ADS)

Akyol, Fatih; Zhang, Yuewei; Krishnamoorthy, Sriram; Rajan, Siddharth

2017-12-01

We report a combination of highly doped layers and polarization engineering that achieves highly efficient blue-transparent GaN/InGaN/GaN tunnel junctions (In content = 12%). NPN diode structures with a low voltage drop of 4.04 V at 5 kA/cm2 and a differential resistance of 6.51 × 10-5 Ω·cm2 at 3 kA/cm2 were obtained. The tunnel junction design with n++-GaN (Si: 5 × 1020 cm-3)/3 nm p++-In0.12Ga0.88N (Mg: 1.5 × 1020 cm-3)/p++-GaN (Mg: 5 × 1020 cm-3) showed the best device performance. Device simulations agree well with the experimentally determined optimal design. The combination of low In composition and high doping can facilitate lower tunneling resistance for blue-transparent light-emitting diodes.

Rapid thermal anneal in InP, GaAs and GaAs/GaAlAs

NASA Astrophysics Data System (ADS)

Descouts, B.; Duhamel, N.; Godefroy, S.; Krauz, P.

Ion implantation in semiconductors provides a doping technique with several advantages over more conventional doping methods and is now extensively used for device applications, e.g. field effect transistors (MESFET GaAs, MIS (InP), GaAs/GaAlAs heterojunction bipolar transistors (HBT). Because of the lattice disorder produced by the implantation, the dopant must be made electrically active by a postimplant anneal. As the device performances are very dependent on its electrical characteristics, the anneal is a very important stage of the process. Rapid anneal is known to provide less exodiffusion and less induffusion of impurities compared to conventional furnace anneal, so this technique has been used in this work to activate an n-type dopant (Si) in InP and a p-type dopant (Mg) in GaAs and GaAs/GaAIAs. These two ions have been chosen to realize implanted MIS InP and the base contacts for GaAs/GaAlAs HBTs. The experimental conditions to obtain the maximum electrical activity in these two cases will be detailed. For example, although we have not been able to obtain a flat profile in Mg + implanted GaAs/GaAlAs heterostructure by conventional thermal anneal, rapid thermal anneal gives a flat hole profile over a depth of 0.5 μm with a concentration of 1 x 10 19 cm -3.

The metalorganic chemical vapor deposition of III-V nitrides for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Grudowski, Paul Alexander

Nitride-based light-emitting diodes (LEDs) and laser diodes are important for large-area LED displays, flat-panel displays, traffic signals, and optical data storage, due to their characteristic ultraviolet and visible light emission. However, much of the research and development addressing material related problems is recent. The room-temperature continuous wave (CW) operation of nitride-based laser diodes remains a major milestone because the material quality requirements for these devices are extremely high. This study investigates nitride material development by the metalorganic chemical vapor deposition (MOCVD) and characterization of GaN, AlGaN, and InGaN, and by qualifying these materials with fabricated devices. The ultimate goal was to develop a working laser diode. The nitride epitaxial films were characterized by 300K Hall effect, x-ray diffraction (XRD), photoluminescence (PL), cathodoluminescence (CL), secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). GaN grown heteroepitaxially on (0001) sapphire substrates was first optimized. A low-temperature GaN nucleation layer was developed that gave subsequent high-temperature GaN layers with low background carrier concentrations (n < 1×10sp{17}\\ cmsp{-3}). Intentional p-type hole concentrations up to 2× 10sp{18} cmsp{-3} and n-type electron concentrations up to 1× 10sp{19} cmsp{-3} were achieved at 300K with magnesium and silicon, respectively. The ternary alloy Insb{x}Gasb{1-x}N was grown with indium compositions up to x = 0.25. These films exhibited strong and narrow 300K PL bandedge peaks. Multiple-quantum-well structures with Insb{0.13}Gasb{0.87}N wells and Insb{0.03}Gasb{0.97}N barriers were grown and gave enhanced PL intensity compared to single InGaN layers. Modulation-doped MQW's produced enhanced PL intensity compared to uniformly-doped MQW's. 300K photopumping experiments produced stimulated emission from a five-period MQW

Engineering future light emitting diodes and photovoltaics with inexpensive materials: Integrating ZnO and Si into GaN-based devices

NASA Astrophysics Data System (ADS)

Bayram, C.; Shiu, K. T.; Zhu, Y.; Cheng, C. W.; Sadana, D. K.; Teherani, F. H.; Rogers, D. J.; Sandana, V. E.; Bove, P.; Zhang, Y.; Gautier, S.; Cho, C.-Y.; Cicek, E.; Vashaei, Z.; McClintock, R.; Razeghi, M.

2013-03-01

Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our

Improving light extraction of InGaN-based light emitting diodes with a roughened p-GaN surface using CsCl nano-islands.

PubMed

Wei, Tongbo; Kong, Qingfeng; Wang, Junxi; Li, Jing; Zeng, Yiping; Wang, Guohong; Li, Jinmin; Liao, Yuanxun; Yi, Futing

2011-01-17

InGaN-based light emitting diodes (LEDs) with a top nano-roughened p-GaN surface are fabricated using self-assembled CsCl nano-islands as etch masks. Following formation of hemispherical GaN nano-island arrays, electroluminescence (EL) spectra of roughened LEDs display an obvious redshift due to partial compression release in quantum wells through Inductively Coupled Plasma (ICP) etching. At a 350-mA current, the enhancement of light output power of LEDs subjected to ICP treatment with durations of 50, 150 and 250 sec compared with conventional LED have been determined to be 9.2, 70.6, and 42.3%, respectively. Additionally, the extraction enhancement factor can be further improved by increasing the size of CsCl nano-island. The economic and rapid method puts forward great potential for high performance lighting devices.

AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

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

Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Anaya Calvo, J.; Kuball, M.

2013-11-11

AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reducedmore » channel thermal conductivity must be considered.« less

Study of GaN nanorods converted from β-Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yuewen; Xiong, Zening; Zhang, Dongdong; Xiu, Xiangqian; Liu, Duo; Wang, Shuang; Hua, Xuemei; Xie, Zili; Tao, Tao; Liu, Bin; Chen, Peng; Zhang, Rong; Zheng, Youdou

2018-05-01

We report here high-quality β-Ga2O3 nanorods (NRs) grown on sapphire substrates by hydrothermal method. Ammoniating the β-Ga2O3 NRs results in strain-free wurtzite gallium nitride (GaN) NRs. It was shown by XRD and Raman spectroscopy that β-Ga2O3 was partially converted to GaN/β-Ga2O3 at 1000 °C and then completely converted to GaN NRs at 1050 °C, as confirmed by high-resolution transmission electron microscopy (HRTEM). There is no band-edge emission of β-Ga2O3 in the cathodoluminescence spectrum, and only a deep-level broad emission observed at 3.68-3.73 eV. The band edge emission (3.39 eV) of GaN NRs converted from β-Ga2O3 can also be observed.

Photoluminescence emission from GaAs nanodisks in GaAs/AlGaAs nanopillar arrays fabricated by neutral beam etching

NASA Astrophysics Data System (ADS)

Ohori, Daisuke; Fukuyama, Atsuhiko; Sakai, Kentaro; Higo, Akio; Thomas, Cedric; Samukawa, Seiji; Ikari, Tetsuo

2017-05-01

GaAs quantum nanodisks (QNDs) in nanopillar (NP) arrays are considered to be an attractive candidate for photonic device applications. We report a damageless fabrication technique that can be used to produce large-area lattice-matched GaAs/AlGaAs heterostructure NP arrays through the use of a bio-template and neutral beam etching. We have successfully realized GaAs QNDs in NPs owing to nanoscale iron oxide masks included in poly(ethylene glycol)-decorated ferritin protein shells. We observed for first time the photoluminescence emission from as-etched GaAs QNDs and confirmed quantum confinement by quantum mechanical calculation. Our methodology is vital for high-efficiency pillar-based optoelectronic devices such as NP laser diodes.

Capacitive coupling in hybrid graphene/GaAs nanostructures

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

Simonet, Pauline, E-mail: psimonet@phys.ethz.ch; Rössler, Clemens; Krähenmann, Tobias

2015-07-13

Coupled hybrid nanostructures are demonstrated using the combination of lithographically patterned graphene on top of a two-dimensional electron gas (2DEG) buried in a GaAs/AlGaAs heterostructure. The graphene forms Schottky barriers at the surface of the heterostructure and therefore allows tuning the electronic density of the 2DEG. Conversely, the 2DEG potential can tune the graphene Fermi energy. Graphene-defined quantum point contacts in the 2DEG show half-plateaus of quantized conductance in finite bias spectroscopy and display the 0.7 anomaly for a large range of densities in the constriction, testifying to their good electronic properties. Finally, we demonstrate that the GaAs nanostructure canmore » detect charges in the vicinity of the heterostructure's surface. This confirms the strong coupling of the hybrid device: localized states in the graphene ribbon could, in principle, be probed by the underlying confined channel. The present hybrid graphene/GaAs nanostructures are promising for the investigation of strong interactions and coherent coupling between the two fundamentally different materials.« less

Injection of Spin-Polarized Electrons into a AlGaN/GaN Device from an Electrochemical Cell: Evidence for an Extremely Long Spin Lifetime.

PubMed

Kumar, Anup; Capua, Eyal; Fontanesi, Claudio; Carmieli, Raanan; Naaman, Ron

2018-04-24

Spin-polarized electrons are injected from an electrochemical cell through a chiral self-assembled organic monolayer into a AlGaN/GaN device in which a shallow two-dimensional electron gas (2DEG) layer is formed. The injection is monitored by a microwave signal that indicates a coherent spin lifetime that exceeds 10 ms at room temperature. The signal was found to be magnetic field independent; however, it depends on the current of the injected electrons, on the length of the chiral molecules, and on the existence of 2DEG.

Using the Arduino with MakerPlot Software for the Display of Electrical Device Characteristics

ERIC Educational Resources Information Center

Atkin, Keith

2017-01-01

This paper shows how very simple circuitry attached to an Arduino microcontroller with MakerPlot software can be used for the display of electrical characteristic curves of three commonly available devices: an ohmic resistor, an LED, and a tungsten-filament bulb.

Using the Arduino with MakerPlot software for the display of electrical device characteristics

NASA Astrophysics Data System (ADS)

Atkin, Keith

2017-11-01

This paper shows how very simple circuitry attached to an Arduino microcontroller with MakerPlot software can be used for the display of electrical characteristic curves of three commonly available devices: an ohmic resistor, an LED, and a tungsten-filament bulb.

Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices

PubMed Central

Anderson, Travis; Ren, Fan; Pearton, Stephen; Kang, Byoung Sam; Wang, Hung-Ta; Chang, Chih-Yang; Lin, Jenshan

2009-01-01

In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs). ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO2 and C2H4 using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application. PMID:22408548

A perfect spin filtering device through Mach-Zehnder interferometry in a GaAs/AlGaAs electron gas

NASA Astrophysics Data System (ADS)

López, Alexander; Medina, Ernesto; Bolívar, Nelson; Berche, Bertrand

2010-03-01

A spin filtering device based on quantum spin interference is addressed, for use with a two-dimensional GaAs/AlGaAs electron gas that has both Rashba and Dresselhaus spin-orbit (SO) couplings and an applied external magnetic field. We propose an experimentally feasible electronic Mach-Zehnder interferometer and derive a map, in parameter space, that determines perfect spin filtering conditions. We find two broad spin filtering regimes: one where filtering is achieved in the original incoming quantization basis, that takes advantage of the purely non-Abelian nature of the spin rotations; and another where one needs a tilted preferential axis in order to observe the polarized output spinor. Both solutions apply for arbitrary incoming electron polarization and energy, and are only limited in output amplitude by the randomness of the incoming spinor state. Including a full account of the beam splitter and mirror effects on spin yields solutions only for the tilted basis, but encompasses a broad range of filtering conditions.

A perfect spin filtering device through Mach-Zehnder interferometry in a GaAs/AlGaAs electron gas.

PubMed

López, Alexander; Medina, Ernesto; Bolívar, Nelson; Berche, Bertrand

2010-03-24

A spin filtering device based on quantum spin interference is addressed, for use with a two-dimensional GaAs/AlGaAs electron gas that has both Rashba and Dresselhaus spin-orbit (SO) couplings and an applied external magnetic field. We propose an experimentally feasible electronic Mach-Zehnder interferometer and derive a map, in parameter space, that determines perfect spin filtering conditions. We find two broad spin filtering regimes: one where filtering is achieved in the original incoming quantization basis, that takes advantage of the purely non-Abelian nature of the spin rotations; and another where one needs a tilted preferential axis in order to observe the polarized output spinor. Both solutions apply for arbitrary incoming electron polarization and energy, and are only limited in output amplitude by the randomness of the incoming spinor state. Including a full account of the beam splitter and mirror effects on spin yields solutions only for the tilted basis, but encompasses a broad range of filtering conditions.

Development of the self-learning machine for creating models of microprocessor of single-phase earth fault protection devices in networks with isolated neutral voltage above 1000 V

NASA Astrophysics Data System (ADS)

Utegulov, B. B.; Utegulov, A. B.; Meiramova, S.

2018-02-01

The paper proposes the development of a self-learning machine for creating models of microprocessor-based single-phase ground fault protection devices in networks with an isolated neutral voltage higher than 1000 V. Development of a self-learning machine for creating models of microprocessor-based single-phase earth fault protection devices in networks with an isolated neutral voltage higher than 1000 V. allows to effectively implement mathematical models of automatic change of protection settings. Single-phase earth fault protection devices.

Design and fabrication of AlGaInP-based micro-light-emitting-diode array devices

NASA Astrophysics Data System (ADS)

Bao, Xingzhen; Liang, Jingqiu; Liang, Zhongzhu; Wang, Weibiao; Tian, Chao; Qin, Yuxin; Lü, Jinguang

2016-04-01

An integrated high-resolution (individual pixel size 80 μm×80 μm) solid-state self-emissive active matrix programmed with 320×240 micro-light-emitting-diode arrays structure was designed and fabricated on an AlGaInP semiconductor chip using micro electro-mechanical systems, microstructure and semiconductor fabricating techniques. Row pixels share a p-electrode and line pixels share an n-electrode. We experimentally investigated GaAs substrate thickness affects the electrical and optical characteristics of the pixels. For a 150-μm-thick GaAs substrate, the single pixel output power was 167.4 μW at 5 mA, and increased to 326.4 μW when current increase to 10 mA. The device investigated potentially plays an important role in many fields.

Trimethylamine alane for low-pressure MOVPE growth of AlGaAs-based materials and device structures

NASA Astrophysics Data System (ADS)

Schneider, R. P.; Bryan, R. P.; Jones, E. D.; Biefield, R. M.; Olbright, G. R.

The use of trimethylamine alane (TMAA1) as an alternative to trimethylaluminum (TMA1) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films as well as complex optoelectronic device structures has been studied in detail. AlGaAs layers were grown in a horizontal reaction chamber at 20 - 110 mbar with growth temperatures in the range 650 C less than or equal to T(sub G) less than or equal to 750 C. Wafer thickness uniformity is strongly dependent on growth pressure, and is acceptable only for the highest linear flow velocities. The 12 K photoluminescence (PL) spectra of AlGaAs layers grown using TMAA1 and TEGa exhibit uniformly intense and narrow bound-exciton emission throughout the growth temperature range investigated. To assess the viability of this new source for the low-pressure OMVPE growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser (VCSEL) structures were grown using TMAA1 extensively. Room temperature lasing at 850 nm was reproducibly obtained from the VCSEL structures, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.

Analysis of improved dc and ac performances of an InGaP/GaAs heterojunction bipolar transistor with a graded Al xGa 1- xAs layer at emitter/base heterojunction

NASA Astrophysics Data System (ADS)

Cheng, Shiou-Ying

2004-07-01

An InGaP/GaAs heterojunction bipolar transistor (HBT) with a continuous conduction-band structure is demonstrated and theoretically investigated. This device exhibited good performance including lower turn-on voltage, lower offset voltage and smaller collector current saturation voltage. The novel aspect of device structure design is the adoption of the compositionally linear-graded AlGaAs layer between the InGaP-emitter and GaAs-base layers. Therefore, the device studied shows better dc and ac performances than a conventional device. Consequently, this causes the substantial benefit for practical analog and digital applications especially for lower operation voltage, lower power consumption commercial and military products.

Open-Gated pH Sensor Fabricated on an Undoped-AlGaN/GaN HEMT Structure

PubMed Central

Abidin, Mastura Shafinaz Zainal; Hashim, Abdul Manaf; Sharifabad, Maneea Eizadi; Rahman, Shaharin Fadzli Abd; Sadoh, Taizoh

2011-01-01

The sensing responses in aqueous solution of an open-gated pH sensor fabricated on an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure are investigated. Under air-exposed ambient conditions, the open-gated undoped AlGaN/GaN HEMT only shows the presence of a linear current region. This seems to show that very low Fermi level pinning by surface states exists in the undoped AlGaN/GaN sample. In aqueous solution, typical current-voltage (I-V) characteristics with reasonably good gate controllability are observed, showing that the potential of the AlGaN surface at the open-gated area is effectively controlled via aqueous solution by the Ag/AgCl gate electrode. The open-gated undoped AlGaN/GaN HEMT structure is capable of distinguishing pH level in aqueous electrolytes and exhibits linear sensitivity, where high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, VDS = 5 V is obtained. Due to the large leakage current where it increases with the negative gate voltage, Nernstian like sensitivity cannot be determined as commonly reported in the literature. This large leakage current may be caused by the technical factors rather than any characteristics of the devices. Surprisingly, although there are some imperfections in the device preparation and measurement, the fabricated devices work very well in distinguishing the pH levels. Suppression of current leakage by improving the device preparation is likely needed to improve the device performance. The fabricated device is expected to be suitable for pH sensing applications. PMID:22163786

Design and fabrication of directional diffractive device on glass substrate for multiview holographic 3D display

NASA Astrophysics Data System (ADS)

Su, Yanfeng; Cai, Zhijian; Liu, Quan; Zou, Wenlong; Guo, Peiliang; Wu, Jianhong

2018-01-01

Multiview holographic 3D display based on the nano-grating patterned directional diffractive device can provide 3D images with high resolution and wide viewing angle, which has attracted considerable attention. However, the current directional diffractive device fabricated on the photoresist is vulnerable to damage, which will lead to the short service life of the device. In this paper, we propose a directional diffractive device on glass substrate to increase its service life. In the design process, the period and the orientation of the nano-grating at each pixel are carefully calculated accordingly by the predefined position of the viewing zone, and the groove parameters are designed by analyzing the diffraction efficiency of the nano-grating pixel on glass substrate. In the experiment, a 4-view photoresist directional diffractive device with a full coverage of pixelated nano-grating arrays is efficiently fabricated by using an ultraviolet continuously variable spatial frequency lithography system, and then the nano-grating patterns on the photoresist are transferred to the glass substrate by combining the ion beam etching and the reactive ion beam etching for controlling the groove parameters precisely. The properties of the etched glass device are measured under the illumination of a collimated laser beam with a wavelength of 532nm. The experimental results demonstrate that the light utilization efficiency is improved and optimized in comparison with the photoresist device. Furthermore, the fabricated device on glass substrate is easier to be replicated and of better durability and practicability, which shows great potential in the commercial applications of 3D display terminal.

Selective epitaxial growth of monolithically integrated GaN-based light emitting diodes with AlGaN/GaN driving transistors

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

Liu, Zhaojun; Ma, Jun; Huang, Tongde

2014-03-03

In this Letter, we report selective epitaxial growth of monolithically integrated GaN-based light emitting diodes (LEDs) with AlGaN/GaN high-electron-mobility transistor (HEMT) drivers. A comparison of two integration schemes, selective epitaxial removal (SER), and selective epitaxial growth (SEG) was made. We found the SER resulted in serious degradation of the underlying LEDs in a HEMT-on-LED structure due to damage of the p-GaN surface. The problem was circumvented using the SEG that avoided plasma etching and minimized device degradation. The integrated HEMT-LEDs by SEG exhibited comparable characteristics as unintegrated devices and emitted modulated blue light by gate biasing.

A review of the synthesis of reduced defect density InxGa1-xN for all indium compositions

NASA Astrophysics Data System (ADS)

Clinton, Evan A.; Vadiee, Ehsan; Fabien, Chloe A. M.; Moseley, Michael W.; Gunning, Brendan P.; Doolittle, W. Alan; Fischer, Alec M.; Wei, Yong O.; Xie, Hongen; Ponce, Fernando A.

2017-10-01

A review of metal rich and nitrogen rich (N-rich), low-temperature grown InxGa1-xN is provided, focusing on two low-temperature approaches that have resulted in non-phase separated InxGa1-xN. The metal modulated epitaxy (MME) and N-rich, low temperature approaches to the reduction of defects in InxGa1-xN are described and are capable of growing InxGa1-xN throughout the miscibility gap. MME films remain smooth at all thicknesses but show device quality material primarily for x < 0.2 and x > 0.6. Low temperature, N-rich grown films show a critical thickness extend well beyond the theoretical values and results in slower relaxation through the 0.2 < x < 0.6 range most interesting for light emitters and solar cells. This reduced defect density results in improved optical emission, but due to increased roughening with increased thickness, low temperature, N-rich films are limited to thin layers. Future thick InxGa1-xN substrates are necessary to increase design freedom, as well as improve optoelectronic device performance. Initial results with films up to 800 nm are shown to display evidence of defect annihilation which could be promising for future thick optoelectronic templates and thick devices.

GaN HEMTs with p-GaN gate: field- and time-dependent degradation

NASA Astrophysics Data System (ADS)

Meneghesso, G.; Meneghini, M.; Rossetto, I.; Canato, E.; Bartholomeus, J.; De Santi, C.; Trivellin, N.; Zanoni, E.

2017-02-01

GaN-HEMTs with p-GaN gate have recently demonstrated to be excellent normally-off devices for application in power conversion systems, thanks to the high and robust threshold voltage (VTH>1 V), the high breakdown voltage, and the low dynamic Ron increase. For this reason, studying the stability and reliability of these devices under high stress conditions is of high importance. This paper reports on our most recent results on the field- and time-dependent degradation of GaN-HEMTs with p-GaN gate submitted to stress with positive gate bias. Based on combined step-stress experiments, constant voltage stress and electroluminescence testing we demonstrated that: (i) when submitted to high/positive gate stress, the transistors may show a negative threshold voltage shift, that is ascribed to the injection of holes from the gate metal towards the p-GaN/AlGaN interface; (ii) in a step-stress experiment, the analyzed commercial devices fail at gate voltages higher than 9-10 V, due to the extremely high electric field over the p-GaN/AlGaN stack; (iii) constant voltage stress tests indicate that the failure is also time-dependent and Weibull distributed. The several processes that can explain the time-dependent failure are discussed in the following.

Design consideration of δ-doping channels for high-performance n + - GaAs / p + -InGaP/n-GaAs camel-gate field effect transistors

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui; Chen, Jeng-Shyan; Chu, Yu-Jui

2005-01-01

The influence of δ-doping channels on the performance of n +-GaAs/p +-InGaP/n-GaAs camel-gate field effect transistors is investigated by theoretical analysis and experimental results. The depleted pn junction of the camel gate and the existence of considerable conduction band discontinuity at the InGaP/GaAs heterojunction enhance the potential barrier height and the forward gate voltage. As the concentration-thickness products of the n-GaAs layer and δ-doping layer are fixed, the higher δ-doping device exhibits a higher potential barrier height, a larger drain current, and a broader gate voltage swing, whereas the transconductance is somewhat lower. For a n +=5.5×10 12 cm -2δ-doping device, the experimental result exhibits a maximum transconductance of 240 mS/mm and a gate voltage swing of 3.5 V. Consequently, the studied devices provide a good potential for large signal and linear circuit applications.

GaSbBi/GaSb quantum well laser diodes

NASA Astrophysics Data System (ADS)

Delorme, O.; Cerutti, L.; Luna, E.; Narcy, G.; Trampert, A.; Tournié, E.; Rodriguez, J.-B.

2017-05-01

We report on the structural and optical properties of GaSbBi single layers and GaSbBi/GaSb quantum well heterostructures grown by molecular beam epitaxy on GaSb substrates. Excellent crystal quality and room-temperature photoluminescence are achieved in both cases. We demonstrate laser operation from laser diodes with an active zone composed of three GaSb0.885Bi0.115/GaSb quantum wells. These devices exhibit continuous-wave lasing at 2.5 μm at 80 K, and lasing under pulsed operation at room-temperature near 2.7 μm.

Rectification and Photoconduction Mapping of Axial Metal-Semiconductor Interfaces Embedded in GaAs Nanowires

NASA Astrophysics Data System (ADS)

Orrù, Marta; Piazza, Vincenzo; Rubini, Silvia; Roddaro, Stefano

2015-10-01

Semiconductor nanowires have emerged as an important enabling technology and are today used in many advanced device architectures, with an impact both for what concerns fundamental science and in view of future applications. One of the key challenges in the development of nanowire-based devices is the fabrication of reliable nanoscale contacts. Recent developments in the creation of metal-semiconductor junctions by thermal annealing of metallic electrodes offer promising perspectives. Here, we analyze the optoelectronic properties of nano-Schottky barriers obtained thanks to the controlled formation of metallic AuGa regions in GaAs nanowire. The junctions display a rectifying behavior and their transport characteristics are analyzed to extract the average ideality factor and barrier height in the current architecture. The presence, location, and properties of the Schottky junctions are cross-correlated with spatially resolved photocurrent measurements. Broadband light emission is reported in the reverse breakdown regime; this observation, combined with the absence of electroluminescence at forward bias, is consistent with the device unipolar nature.

GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

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

Islam, Sk Masiul, E-mail: masiulelt@gmail.com; Chowdhury, Sisir; Sarkar, Krishnendu

2015-06-24

Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO{sub 2} and ZrO{sub 2}, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×10{sup 11} cm{sup −2}, respectively. The device with a structure Metal/ZrO{sub 2}/InAs QDs/HfO{sub 2}/GaAs/Metal shows maximum memory window equivalent to 6.87 V. Themore » device also exhibits low leakage current density of the order of 10{sup −6} A/cm{sup 2} and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO{sub 2} deposition.« less

Single photon emission of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As droplet quantum dot device

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

Langer, Fabian, E-mail: fabian.langer@physik.uni-wuerzburg.de; Plischke, David; Kamp, Martin

2014-08-25

In this work, we report the fabrication of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As quantum dot (QD) device containing QDs deposited by modified droplet epitaxy producing almost strain and composition gradient free QDs. We obtained a QD density in the low 10{sup 9 }cm{sup −2} range that enables us to perform spectroscopy on single droplet QDs showing linewidths as narrow as 40 μeV. The integration of the QDs into a Schottky diode allows us to controllably charge a single QD with up to four electrons, while non-classical photoluminescence is proven by photon auto-correlation measurements showing photon-antibunching (g{sup (2)}(0) = 0.05).

Defect evolution during catastrophic optical damage in 450-nm emitting InGaN/GaN diode lasers

NASA Astrophysics Data System (ADS)

Tomm, Jens W.; Kernke, Robert; Löffler, Andreas; Stojetz, Bernhard; Lell, Alfred; König, Harald

2018-02-01

The catastrophic optical damage (COD) of 450-nm emitting InGaN/GaN diode lasers is investigated with special attention to the kinetics of the process. For this purpose, the COD is triggered artificially by applying individual current pulses. This makes it possible to achieve a sub-µs time resolution for processes monitored by cameras. COD appears as a "hot" process that involves decomposition of quantum well and waveguide materials. We observe the ejection of hot material from the front facets of the laser. This can be seen in two different wavelength ranges, visible/near infrared and mid infrared. The main contributions identified are both thermal radiation and 450-nm laser light scattered by the emitted material. Defect growth during COD is energized by the optical mode. Therefore, the defect pattern resembles its shape. Ultimately, the loss of material leads to the formation of an empty channel along the laser axis. COD in GaAs and GaN-based devices follows similar general scenarios. After ignition of the process, the defect propagation during the process is fed by laser energy. We observe defect propagation velocities of up to 30 m/s for GaAs-based devices and 110 m/s for GaN-based devices. The damage patterns of GaN and GaAs-based devices are completely different. For GaN-based devices, the front facets show holes. Behind them in the interior, we find an empty channel at the position of the optical mode surrounded by intact material. In contrast, earlier studies on GaAs-based devices that were degraded under almost identical conditions resulted in molten, phase separated and both recrystallized and amorphous materials with well-defined melting fronts.

Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

NASA Astrophysics Data System (ADS)

Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

2004-09-01

In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

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

Kim, Jaehwan; Min, Daehong; Jang, Jongjin

2014-10-28

In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface.more » To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.« less

The effect of (NH4)2Sx passivation on the (311)A GaAs surface and its use in AlGaAs/GaAs heterostructure devices.

PubMed

Carrad, D J; Burke, A M; Reece, P J; Lyttleton, R W; Waddington, D E J; Rai, A; Reuter, D; Wieck, A D; Micolich, A P

2013-08-14

We have studied the efficacy of (NH4)2Sx surface passivation on the (311)A GaAs surface. We report XPS studies of simultaneously-grown (311)A and (100) heterostructures showing that the (NH4)2Sx solution removes surface oxide and sulfidizes both surfaces. Passivation is often characterized using photoluminescence measurements; we show that while (NH4)2Sx treatment gives a 40-60 ×  increase in photoluminescence intensity for the (100) surface, an increase of only 2-3 ×  is obtained for the (311)A surface. A corresponding lack of reproducible improvement in the gate hysteresis of (311)A heterostructure transistor devices made with the passivation treatment performed immediately prior to gate deposition is also found. We discuss possible reasons why sulfur passivation is ineffective for (311)A GaAs, and propose alternative strategies for passivation of this surface.

Design of quantum efficiency measurement system for variable doping GaAs photocathode

NASA Astrophysics Data System (ADS)

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Normally-off Al2O3/GaN MOSFET: Role of border traps on the device transport characteristics

NASA Astrophysics Data System (ADS)

Wang, Hongyue; Wang, Jinyan; Liu, Jingqian; He, Yandong; Wang, Maojun; Yu, Min; Wu, Wengang

2018-03-01

Based on the self-terminating gate recess technique, two different processes featuring gate-recess-first (GF) and ohmic-contact-first (OF) were proposed for E-mode Al2O3/GaN MOSFETs. Increased maximum drain current (Idmax) ∼30% (420 vs 325 mA/mm), field-effect mobility (μFEmax) ∼67% (150 vs 90 cm2/Vs) and reduced on-state resistance (Ron) ∼42% (9.7 vs 16.8 Ω·mm) were observed in the devices fabricated by GF process. Such significant performance difference of GF- and OF-devices resulted from the presence of border traps at Al2O3/GaN interface with a time constant ∼7 × 10-6 s. Experimental results indicated that: (1) the near interface border traps in Al2O3 dielectric significantly affect device channel mobility; (2) a high temperature post-deposition annealing process could effective suppress generation of border traps.

Recent advances of high voltage AlGaN/GaN power HFETs

NASA Astrophysics Data System (ADS)

Uemoto, Yasuhiro; Ueda, Tetsuzo; Tanaka, Tsuyoshi; Ueda, Daisuke

2009-02-01

We review our recent advances of GaN-based high voltage power transistors. These are promising owing to low on-state resistance and high breakdown voltage taking advantages of superior material properties. However, there still remain a couple of technical issues to be solved for the GaN devices to replace the existing Si-based power devices. The most critical issue is to achieve normally-off operation which is strongly desired for the safety operation, however, it has been very difficult because of the built-in polarization electric field. Our new device called GIT (Gate Injection Transistor) utilizing conductivity modulation successfully achieves the normally-off operation keeping low on-state resistance. The fabricated GIT on a Si substrate exhibits threshold voltage of +1.0V. The obtained on-state resistance and off-state breakdown voltage were 2.6mΩ•cm2 and 800V, respectively. Remaining technical issue is to further increase the breakdown voltage. So far, the reported highest off-state breakdown voltage of AlGaN/GaN HFETs has been 1900V. Overcoming these issues by a novel device structure, we have demonstrated the world highest breakdown voltages of 10400V using thick poly-crystalline AlN as a passivation film and Via-holes through sapphire which enable very efficient layout of the lateral HFET array avoiding any undesired breakdown of passivation films. Since conventional wet or dry etching cannot be used for chemically stable sapphire, high power pulsed laser is used to form the via-holes. The presented GaN power devices demonstrate that GaN is advantageous for high voltage power switching applications replacing currently used Si-based power MOSFETs and IGBTs.

InGaN pn-junctions grown by PA-MBE: Material characterization and fabrication of nanocolumn electroluminescent devices

NASA Astrophysics Data System (ADS)

Gherasoiu, I.; Yu, K. M.; Reichertz, L.; Walukiewicz, W.

2015-09-01

PN junctions are basic building blocks of many electronic devices and their performance depends on the structural properties of the component layers and on the type and the amount of the doping impurities incorporated. Magnesium is the common p-type dopant for nitride semiconductors while silicon and more recently germanium are the n-dopants of choice. In this paper, therefore we analyze the quantitative limits for Mg and Ge incorporation on GaN and InGaN with high In content. We also discuss the challenges posed by the growth and characterization of InGaN pn-junctions and we discuss the properties of large area, long wavelength nanocolumn LEDs grown on silicon (1 1 1) by PA-MBE.

Photo-recovery of electron-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Meulenberg, Andrew

1995-01-01

The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.

Design analysis of phosphor-free monolithic white light-emitting-diodes with InGaN/ InGaN multiple quantum wells on ternary InGaN substrates

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

Ooi, Yu Kee, E-mail: Yu.Kee.Ooi@rit.edu; Zhang, Jing, E-mail: Jing.Zhang@rit.edu

2015-05-15

Phosphor-free monolithic white light emitting diodes (LEDs) based on InGaN/ InGaN multiple quantum wells (MQWs) on ternary InGaN substrates are proposed and analyzed in this study. Simulation studies show that LED devices composed of multi-color-emitting InGaN/ InGaN quantum wells (QWs) employing ternary InGaN substrate with engineered active region exhibit stable white color illumination with large output power (∼ 170 mW) and high external quantum efficiency (EQE) (∼ 50%). The chromaticity coordinate for the investigated monolithic white LED devices are located at (0.30, 0.28) with correlated color temperature (CCT) of ∼ 8200 K at J = 50 A/cm{sup 2}. A referencemore » LED device without any nanostructure engineering exhibits green color emission shows that proper engineered structure is essential to achieve white color illumination. This proof-of-concept study demonstrates that high-efficiency and cost-effective phosphor-free monolithic white LED is feasible by the use of InGaN/ InGaN MQWs on ternary InGaN substrate combined with nanostructure engineering, which would be of great impact for solid state lighting.« less

Direct observation of trapped charges under field-plate in p-GaN gate AlGaN/GaN high electron mobility transistors by electric field-induced optical second-harmonic generation

NASA Astrophysics Data System (ADS)

Katsuno, Takashi; Manaka, Takaaki; Soejima, Narumasa; Iwamoto, Mitsumasa

2017-02-01

Trapped charges underneath the field-plate (FP) in a p-gallium nitride (GaN) gate AlGaN/ GaN high electron mobility transistor device were visualized by using electric field-induced optical second-harmonic generation imaging. Second-harmonic (SH) signals in the off-state of the device with FP indicated that the electric field decreased at the p-GaN gate edge and concentrated at the FP edge. Nevertheless, SH signals originating from trapped charges were slightly observed at the p-GaN gate edge and were not observed at the FP edge in the on-state. Compared with the device without FP, reduction of trapped charges at the p-GaN gate edge of the device with FP is attributed to attenuation of the electric field with the aid of the FP. Negligible trapped charges at the FP edge is owing to lower trap density of the SiO2/AlGaN interface at the FP edge compared with that of the SiO2/p-GaN sidewall interface at the p-GaN gate edge and attenuated electric field by the thickness of the SiO2 passivation layer on the AlGaN surface.

Designing optically pumped InGaN quantum wells with long wavelength emission for a phosphor-free device with polarized white-light emission

NASA Astrophysics Data System (ADS)

Kowsz, Stacy J.; Pynn, Christopher D.; Wu, Feng; Farrell, Robert M.; Speck, James S.; DenBaars, Steven P.; Nakamura, Shuji

2016-02-01

We report a semipolar III-nitride device in which an electrically injected blue light emitting diode optically pumps monolithic long wavelength emitting quantum wells (QWs) to create polarized white light. We have demonstrated an initial device with emission peaks at 440 nm and 560 nm from the electrically injected and optically pumped QWs, respectively. By tuning the ratio of blue to yellow, white light was measured with a polarization ratio of 0.40. High indium content InGaN is required for long wavelength emission but is difficult to achieve because it requires low growth temperatures and has a large lattice mismatch with GaN. This device design incorporates optically pumped QWs for long wavelength emission because they offer advantages over using electrically injected QWs. Optically pumped QWs do not have to be confined within a p-n junction, and carrier transport is not a concern. Thus, thick GaN barriers can be incorporated between multiple InGaN QWs to manage stress. Optically pumping long wavelength emitting QWs also eliminates high temperature steps that degrade high indium content InGaN but are required when growing p-GaN for an LED structure. Additionally, by eliminating electrical injection, the doping profile can instead be engineered to affect the emission wavelength. We discuss ongoing work focused on improving polarized white light emission by optimizing the optically pumped QWs. We consider the effects of growth conditions, including: trimethylindium (TMI) flow rate, InGaN growth rate, and growth temperature. We also examine the effects of epitaxial design, including: QW width, number of QWs, and doping.

77 FR 74220 - Certain Digital Photo Frames and Image Display Devices and Components Thereof; Commission...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-13

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-807] Certain Digital Photo Frames and Image Display Devices and Components Thereof; Commission Determination Not To Review an Initial... importation, and the sale within the United States after importation of certain digital photo frames and image...

Self-powered fluorescence display devices based on a fast self-charging/recharging battery (Mg/Prussian blue).

PubMed

Zhang, Hui; Yu, You; Zhang, Lingling; Zhai, Yiwen; Dong, Shaojun

2016-11-01

Stimuli-responsive (such as voltage and/or light) fluorescence display systems have attracted particular attention in their promising fields of application. However, there are few examples of self-powered fluorescence display devices. Here we designed and fabricated a self-powered fluorescence display device based on a fast-charging/recharging battery. The specially designed battery was composed of a Prussian blue (PB) cathode and a magnesium metal anode with a high theoretical redox potential difference (∼2.8 V). Moreover, smartly adding a trace amount of NaClO in the electrolyte could realize oxidizing PW to PB ∼480 times faster than when oxidizing without NaClO, leading to the fast self-charging and high power density (maximum power density of 13.34 mW cm -2 , about two to three orders of magnitude larger than previous bio-fuel cells) of the Mg/PB battery. Most importantly, PB was used as not only the cathodic catalyst but also as an electrochromic material, making it possible to construct a self-powered and rechargeable electrochromic fluorescence display with only two electrodes. Besides, fluorescent [Ru(bpy) 3 ] 2+ -doped silica nanoparticles (Ru@SiO 2 ), were selected as the fluorescence resonance energy transfer (FRET) donor to match PB (FRET acceptor). To the best of our knowledge, we demonstrated a self-powered and rechargeable electrochromic fluorescence display with only two electrodes for the first time.

Enhanced quality thin film Cu(In,Ga)Se.sub.2 for semiconductor device applications by vapor-phase recrystallization

DOEpatents

Tuttle, John R.; Contreras, Miguel A.; Noufi, Rommel; Albin, David S.

1994-01-01

Enhanced quality thin films of Cu.sub.w (In,Ga.sub.y)Se.sub.z for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu.sub.x Se on a substrate to form a large-grain precursor and then converting the excess Cu.sub.x Se to Cu(In,Ga)Se.sub.2 by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga).sub.y Se.sub.z. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300.degree.-600.degree. C., where the Cu(In,Ga)Se.sub.2 remains solid, while the excess Cu.sub.x Se is in a liquid flux. The characteristic of the resulting Cu.sub.w (In,Ga).sub.y Se.sub.z can be controlled by the temperature. Higher temperatures, such as 500.degree.-600.degree. C., result in a nearly stoichiometric Cu(In,Ga)Se.sub.2, whereas lower temperatures, such as 300.degree.-400.degree. C., result in a more Cu-poor compound, such as the Cu.sub.z (In,Ga).sub.4 Se.sub.7 phase.

Enhanced quality thin film Cu(In,Ga)Se[sub 2] for semiconductor device applications by vapor-phase recrystallization

DOEpatents

Tuttle, J.R.; Contreras, M.A.; Noufi, R.; Albin, D.S.

1994-10-18

Enhanced quality thin films of Cu[sub w](In,Ga[sub y])Se[sub z] for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu[sub x]Se on a substrate to form a large-grain precursor and then converting the excess Cu[sub x]Se to Cu(In,Ga)Se[sub 2] by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga)[sub y]Se[sub z]. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300--600 C, where the Cu(In,Ga)Se[sub 2] remains solid, while the excess Cu[sub x]Se is in a liquid flux. The characteristic of the resulting Cu[sub w](In,Ga)[sub y]Se[sub z] can be controlled by the temperature. Higher temperatures, such as 500--600 C, result in a nearly stoichiometric Cu(In,Ga)Se[sub 2], whereas lower temperatures, such as 300--400 C, result in a more Cu-poor compound, such as the Cu[sub z](In,Ga)[sub 4]Se[sub 7] phase. 7 figs.

Three-terminal RGB full-color OLED pixels for ultrahigh density displays.

PubMed

Fröbel, Markus; Fries, Felix; Schwab, Tobias; Lenk, Simone; Leo, Karl; Gather, Malte C; Reineke, Sebastian

2018-06-26

In recent years, the organic light-emitting diode (OLED) technology has been a rapidly evolving field of research, successfully making the transition to commercial applications such as mobile phones and other small portable devices. OLEDs provide efficient generation of light, excellent color quality, and allow for innovative display designs, e.g., curved shapes, mechanically flexible and/or transparent devices. Especially their self emissive nature is a highly desirable feature for display applications. In this work, we demonstrate an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows for efficient generation of every color that is accessible by superpositioning the spectra of the individual emission units. Here, we use a combination of time division multiplexing and pulse width modulation to achieve efficient color mixing. The presented device design requires only three independently addressable electrodes, simplifying both fabrication and electrical driving. The device is built in a top-emission geometry, which is highly desirable for display fabrication as the pixel can be directly deposited onto back-plane electronics. Despite the top-emission design and the application of three silver layers within the device, there is only a minor color shift even for large viewing angles. The color space spanned by the three emission sub-units exceeds the sRGB space, providing more saturated green/yellow/red colors. Furthermore, the electrical performance of each individual unit is on par with standard single emission unit OLEDs, showing very low leakage currents and achieving brightness levels above 1000 cd/m 2 at moderate voltages of around 3-4 V.

InGaAsBi alloys on InP for efficient near- and mid-infrared light emitting devices

NASA Astrophysics Data System (ADS)

Jin, Shirong; John Sweeney, Stephen

2013-12-01

We present the band parameters such as band gap, spin-orbit splitting energy, band offsets and strain of InGaAsBi on InP based on recent experimental data. It is shown that InGaAsBi is promising for near- and mid-infrared photonic devices operating from 0.3-0.8 eV (1.5-4 μm) on conventional InP substrates. We also show how bismuth may be used to form alloys whereby the spin-orbit splitting energy (ΔSO) is large and controllable and can, for example, be made larger than the band gap (Eg) thereby providing a means of suppressing non-radiative hot-hole producing Auger recombination and inter-valence band absorption both involving the spin-orbit band. This is expected to improve the high-temperature performance and thermal stability of light emitting devices.

Color tunable monolithic InGaN/GaN LED having a multi-junction structure.

PubMed

Kong, Duk-Jo; Kang, Chang-Mo; Lee, Jun-Yeob; Kim, James; Lee, Dong-Seon

2016-03-21

In this study, we have fabricated a blue-green color-tunable monolithic InGaN/GaN LED having a multi-junction structure with three terminals. The device has an n-p-n structure consisting of a green and a blue active region, i.e., an n-GaN / blue-MQW / p-GaN / green-MQW / n-GaN / Al₂O₃ structure with three terminals for independently controlling the two active regions. To realize this LED structure, a typical LED consisting of layers of n-GaN, blue MQW, and p-GaN is regrown on a conventional green LED by using a metal organic chemical vapor deposition (MOCVD) method. We explain detailed mechanisms of three operation modes which are the green, blue, and cyan mode. Moreover, we discuss optical properties of the device.

AlGaN-Cladding-Free m-Plane InGaN/GaN Laser Diodes with p-Type AlGaN Etch Stop Layers

NASA Astrophysics Data System (ADS)

Farrell, Robert M.; Haeger, Daniel A.; Hsu, Po Shan; Hardy, Matthew T.; Kelchner, Kathryn M.; Fujito, Kenji; Feezell, Daniel F.; Mishra, Umesh K.; DenBaars, Steven P.; Speck, James S.; Nakamura, Shuji

2011-09-01

We present a new method of improving the accuracy and reproducibility of dry etching processes for ridge waveguide InGaN/GaN laser diodes (LDs). A GaN:Al0.09Ga0.91N etch rate selectivity of 11:1 was demonstrated for an m-plane LD with a 40 nm p-Al0.09Ga0.91N etch stop layer (ESL) surrounded by Al-free cladding layers, establishing the effectiveness of AlGaN-based ESLs for controlling etch depth in ridge waveguide InGaN/GaN LDs. These results demonstrate the potential for integrating AlGaN ESLs into commercial device designs where accurate control of the etch depth of the ridge waveguide is necessary for stable, kink-free operation at high output powers.

Separated carbon nanotube macroelectronics for active matrix organic light-emitting diode displays.

PubMed

Zhang, Jialu; Fu, Yue; Wang, Chuan; Chen, Po-Chiang; Liu, Zhiwei; Wei, Wei; Wu, Chao; Thompson, Mark E; Zhou, Chongwu

2011-11-09

Active matrix organic light-emitting diode (AMOLED) display holds great potential for the next generation visual technologies due to its high light efficiency, flexibility, lightweight, and low-temperature processing. However, suitable thin-film transistors (TFTs) are required to realize the advantages of AMOLED. Preseparated, semiconducting enriched carbon nanotubes are excellent candidates for this purpose because of their excellent mobility, high percentage of semiconducting nanotubes, and room-temperature processing compatibility. Here we report, for the first time, the demonstration of AMOLED displays driven by separated nanotube thin-film transistors (SN-TFTs) including key technology components, such as large-scale high-yield fabrication of devices with superior performance, carbon nanotube film density optimization, bilayer gate dielectric for improved substrate adhesion to the deposited nanotube film, and the demonstration of monolithically integrated AMOLED display elements with 500 pixels driven by 1000 SN-TFTs. Our approach can serve as the critical foundation for future nanotube-based thin-film display electronics.

Separated Carbon Nanotube Macroelectronics for Active Matrix Organic Light-Emitting Diode Displays

NASA Astrophysics Data System (ADS)

Fu, Yue; Zhang, Jialu; Wang, Chuan; Chen, Pochiang; Zhou, Chongwu

2012-02-01

Active matrix organic light-emitting diode (AMOLED) display holds great potential for the next generation visual technologies due to its high light efficiency, flexibility, lightweight, and low-temperature processing. However, suitable thin-film transistors (TFTs) are required to realize the advantages of AMOLED. Pre-separated, semiconducting enriched carbon nanotubes are excellent candidates for this purpose because of their excellent mobility, high percentage of semiconducting nanotubes, and room-temperature processing compatibility. Here we report, for the first time, the demonstration of AMOLED displays driven by separated nanotube thin-film transistors (SN-TFTs) including key technology components such as large-scale high-yield fabrication of devices with superior performance, carbon nanotube film density optimization, bilayer gate dielectric for improved substrate adhesion to the deposited nanotube film, and the demonstration of monolithically integrated AMOLED display elements with 500 pixels driven by 1000 SN-TFTs. Our approach can serve as the critical foundation for future nanotube-based thin-film display electronics.

Integrated RGB laser light module for autostereoscopic outdoor displays

NASA Astrophysics Data System (ADS)

Reitterer, Jörg; Fidler, Franz; Hambeck, Christian; Saint Julien-Wallsee, Ferdinand; Najda, Stephen; Perlin, Piotr; Stanczyk, Szymon; Czernecki, Robert; McDougall, Stewart D.; Meredith, Wyn; Vickers, Garrie; Landles, Kennedy; Schmid, Ulrich

2015-02-01

We have developed highly compact RGB laser light modules to be used as light sources in multi-view autostereoscopic outdoor displays and projection devices. Each light module consists of an AlGaInP red laser diode, a GaInN blue laser diode, a GaInN green laser diode, as well as a common cylindrical microlens. The plano-convex microlens is a so-called "fast axis collimator", which is widely used for collimating light beams emitted from high-power laser diode bars, and has been optimized for polychromatic RGB laser diodes. The three light beams emitted from the red, green, and blue laser diodes are collimated in only one transverse direction, the so-called "fast axis", and in the orthogonal direction, the so-called "slow axis", the beams pass the microlens uncollimated. In the far field of the integrated RGB light module this produces Gaussian beams with a large ellipticity which are required, e.g., for the application in autostereoscopic outdoor displays. For this application only very low optical output powers of a few milliwatts per laser diode are required and therefore we have developed tailored low-power laser diode chips with short cavity lengths of 250 μm for red and 300 μm for blue. Our RGB laser light module including the three laser diode chips, associated monitor photodiodes, the common microlens, as well as the hermetically sealed package has a total volume of only 0.45 cm³, which to our knowledge is the smallest RGB laser light source to date.

The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device

DTIC Science & Technology

2011-11-01

stack between the GaN and Substrate layers. The University of Bristol recently reported that this TBR in commercial devices on Silicon Carbide ( SiC ...Circuit RF Radio Frequency PA Power Amplifier SiC Silicon Carbide FEA Finite Element Analysis heff Effective Heat transfer Coefficient (W/m 2 K...substrate material switched from sapphire to silicon , and by another factor of two from silicon to SiC . TABLE 1: SAMPLE RESULTS FROM DOUGLAS ET AL. FOR

Molecular detection via hybrid peptide-semiconductor photonic devices

NASA Astrophysics Data System (ADS)

Estephan, E.; Saab, M.-b.; Martin, M.; Cloitre, T.; Larroque, C.; Cuisinier, F. J. G.; Malvezzi, A. M.; Gergely, C.

2011-03-01

The aim of this work was to investigate the possibilities to support device functionality that includes strongly confined and localized light emission and detection processes within nano/micro-structured semiconductors for biosensing applications. The interface between biological molecules and semiconductor surfaces, yet still under-explored is a key issue for improving biomolecular recognition in devices. We report on the use of adhesion peptides, elaborated via combinatorial phage-display libraries for controlled placement of biomolecules, leading to user-tailored hybrid photonic systems for molecular detection. An M13 bacteriophage library has been used to screen 1010 different peptides against various semiconductors to finally isolate specific peptides presenting a high binding capacity for the target surfaces. When used to functionalize porous silicon microcavities (PSiM) and GaAs/AlGaAs photonic crystals, we observe the formation of extremely thin (<1nm) peptide layers, hereby preserving the nanostructuration of the crystals. This is important to assure the photonic response of these tiny structures when they are functionalized by a biotinylated peptide layer and then used to capture streptavidin. Molecular detection was monitored via both linear and nonlinear optical measurements. Our linear reflectance spectra demonstrate an enhanced detection resolution via PSiM devices, when functionalized with the Si-specific peptide. Molecular capture at even lower concentrations (femtomols) is possible via the second harmonic generation of GaAs/AlGaAs photonic crystals when functionalized with GaAs-specific peptides. Our work demonstrates the outstanding value of adhesion peptides as interface linkers between semiconductors and biological molecules. They assure an enhanced molecular detection via both linear and nonlinear answers of photonic crystals.

Binocular device for displaying numerical information in field of view

NASA Technical Reports Server (NTRS)

Fuller, H. V. (Inventor)

1977-01-01

An apparatus is described for superimposing numerical information on the field of view of binoculars. The invention has application in the flying of radio-controlled model airplanes. Information such as airspeed and angle of attack are sensed on a model airplane and transmitted back to earth where this information is changed into numerical form. Optical means are attached to the binoculars that a pilot is using to track the model air plane for displaying the numerical information in the field of view of the binoculars. The device includes means for focusing the numerical information at infinity whereby the user of the binoculars can see both the field of view and the numerical information without refocusing his eyes.

Analysis of waveguide architectures of InGaN/GaN diode lasers by nearfield optical microscopy

NASA Astrophysics Data System (ADS)

Friede, Sebastian; Tomm, Jens W.; Kühn, Sergei; Hoffmann, Veit; Wenzel, Hans

2017-02-01

Waveguide (WG) architectures of 420-nm emitting InAlGaN/GaN diode lasers are analyzed by photoluminescence (PL) and photocurrent (PC) spectroscopy using a nearfield scanning optical microscope (NSOM) for excitation and detection. The measurements with a spatial resolution of 100 nm are implemented by scanning the fiber tip along the unprepared front facets of standard devices. PL is collected by the fiber tip, whereas PCs are extracted from the contacts that are anyway present for power supply. The mechanisms of signal generation are addressed in detail. The components of the `optical active region', multiple quantum wells (MQW), WGs, and cladding layers are separately inspected. Even separate analysis of p- and n-sections of the WG become possible. Defect levels are detected in the p-part of the WG. Their presence is consistent with the doping by Mg. An increased efficiency of carrier capture into InGaN/GaN WGs compared to GaN WGs is observed. Thus, beyond the improved optical confinement, the electrical confinement is improved, as well. NSOM PL and PC at GaN based devices do not reach the clarity and spatial resolution for WG mode analysis as seen before for GaAs based devices. This is due to higher modal absorption and higher WG losses. NSOM based optical analysis turns out to be an efficient tool for analysis of single layers grown into InAlGaN/GaN diode laser structures, even if this analysis is done at a packaged ready-to-work device.

Deep-level traps in lightly Si-doped n-GaN on free-standing m-oriented GaN substrates

NASA Astrophysics Data System (ADS)

Yamada, H.; Chonan, H.; Takahashi, T.; Yamada, T.; Shimizu, M.

2018-04-01

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm-3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC - 0.24 eV, and the trap concentration at EC - 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers.

Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

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

Yang, Lin'an, E-mail: layang@xidian.edu.cn; Li, Yue; Wang, Ying

Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al{sub 0.15}Ga{sub 0.85}N emitter barrier and a 1.7-nm-thick Al{sub 0.25}Ga{sub 0.75}N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A andmore » 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al{sub 0.2}Ga{sub 0.8}N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In{sub 0.03}Ga{sub 0.97}N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.« less

Process dependency on threshold voltage of GaN MOSFET on AlGaN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Wang, Qingpeng; Jiang, Ying; Miyashita, Takahiro; Motoyama, Shin-ichi; Li, Liuan; Wang, Dejun; Ohno, Yasuo; Ao, Jin-Ping

2014-09-01

GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 1012 q/cm2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl4, BCl3 and two-step etching of SiCl4/Cl2) at the same ICP bias power level (20-25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO3/HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

ZnO Films on {001}-Cut <110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications

NASA Technical Reports Server (NTRS)

Kim, Yoonkee; Hunt, William D.; Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei

1995-01-01

A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

Impact of gate engineering in enhancement mode n++GaN/InAlN/AlN/GaN HEMTs

NASA Astrophysics Data System (ADS)

Adak, Sarosij; Swain, Sanjit Kumar; Rahaman, Hafizur; Sarkar, Chandan Kumar

2016-12-01

This paper illustrate the effect of gate material engineering on the performance of enhancement mode n++GaN/InAlN/AlN/GaN high electron mobility transistors (HEMTs). A comparative analysis of key device parameters is discussed for the Triple Material Gate (TMG), Dual Material Gate (DMG) and the Single Material Gate (SMG) structure HEMTs by considering the same device dimensions. The simulation results shows that an significant improvement is noticed in the key analysis parameters such as drain current (Id), transconductance (gm), cut off frequency (fT), RF current gain, maximum cut off frequency (fmax) and RF power gain of the gate material engineered devices with respect to SMG normally off n++GaN/InAlN/AlN/GaN HEMTs. This improvement is due to the existence of the perceivable step in the surface potential along the channel which successfully screens the drain potential variation in the source side of the channel for the gate engineering devices. The analysis suggested that the proposed TMG and DMG engineered structure enhancement mode n++GaN/InAlN/AlN/GaN HEMTs can be considered as a potential device for future high speed, microwave and digital application.

48 CFR 3.1000 - Scope of subpart.

Code of Federal Regulations, 2010 CFR

2010-10-01

... BUSINESS PRACTICES AND PERSONAL CONFLICTS OF INTEREST Contractor Code of Business Ethics and Conduct 3.1000... codes of business ethics and conduct, and display of agency Office of Inspector General (OIG) fraud...

Study of GaN nanowires converted from β-Ga2O3 and photoconduction in a single nanowire

NASA Astrophysics Data System (ADS)

Kumar, Mukesh; Kumar, Sudheer; Chauhan, Neha; Sakthi Kumar, D.; Kumar, Vikram; Singh, R.

2017-08-01

The formation of GaN nanowires from β-Ga2O3 nanowires and photoconduction in a fabricated single GaN nanowire device has been studied. Wurtzite phase GaN were formed from monoclinic β-Ga2O3 nanowires with or without catalyst particles at their tips. The formation of faceted nanostructures from catalyst droplets presented on a nanowire tip has been discussed. The nucleation of GaN phases in β-Ga2O3 nanowires and their subsequent growth due to interfacial strain energy has been examined using a high resolution transmission electron microscope. The high quality of the converted GaN nanowire is confirmed by fabricating single nanowire photoconducting devices which showed ultra high responsivity under ultra-violet illumination.

Liquid crystal waveguides: new devices enabled by >1000 waves of optical phase control

NASA Astrophysics Data System (ADS)

Davis, Scott R.; Farca, George; Rommel, Scott D.; Johnson, Seth; Anderson, Michael H.

2010-02-01

A new electro-optic waveguide platform, which provides unprecedented voltage control over optical phase delays (> 2mm), with very low loss (< 0.5 dB/cm) and rapid response time (sub millisecond), will be presented. This technology, developed by Vescent Photonics, is based upon a unique liquid-crystal waveguide geometry, which exploits the tremendous electro-optic response of liquid crystals while circumventing their historic limitations. The waveguide geometry provides nematic relaxation speeds in the 10's of microseconds and LC scattering losses that are reduced by orders of magnitude from bulk transmissive LC optics. The exceedingly large optical phase delays accessible with this technology enable the design and construction of a new class of previously unrealizable photonic devices. Examples include: 2-D analog non-mechanical beamsteerers, chip-scale widely tunable lasers, chip-scale Fourier transform spectrometer (< 5 nm resolution demonstrated), widely tunable micro-ring resonators, tunable lenses, ultra-low power (< 5 microWatts) optical switches, true optical time delay devices for phased array antennas, and many more. All of these devices may benefit from established manufacturing technologies and ultimately may be as inexpensive as a calculator display. Furthermore, this new integrated photonic architecture has applications in a wide array of commercial and defense markets including: remote sensing, micro-LADAR, OCT, FSO, laser illumination, phased array radar, etc. Performance attributes of several example devices and application data will be presented. In particular, we will present a non-mechanical beamsteerer that steers light in both the horizontal and vertical dimensions.

Site-controlled InGaN/GaN single-photon-emitting diode

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

Zhang, Lei; Deng, Hui, E-mail: dengh@umich.edu; Teng, Chu-Hsiang

2016-04-11

We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots. The device is fabricated from a planar light-emitting diode structure containing a single InGaN quantum well, using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

PLASMAP: an interactive computational tool for storage, retrieval and device-independent graphic display of conventional restriction maps.

PubMed Central

Stone, B N; Griesinger, G L; Modelevsky, J L

1984-01-01

We describe an interactive computational tool, PLASMAP, which allows the user to electronically store, retrieve, and display circular restriction maps. PLASMAP permits users to construct libraries of plasmid restriction maps as a set of files which may be edited in the laboratory at any time. The display feature of PLASMAP quickly generates device-independent, artist-quality, full-color or monochrome, hard copies or CRT screens of complex, conventional circular restriction maps. PMID:6320096

Near-infrared cathodoluminescence imaging of defect distributions in In(0.2)Ga(0.8)As/GaAs multiple quantum wells grown on prepatterned GaAs

NASA Technical Reports Server (NTRS)

Rich, D. H.; Fajkumar, K. C.; Chen, LI; Madhukar, A.; Grunthaner, F. J.

1992-01-01

The defect distribution in a highly strained In(0.2)Ga(0.8)As/GaAs multiple-quantum-well (MQW) structure grown on a patterned GaAs substrate is examined with cathodoluminescence imaging and spectroscopy in the near IR. By spatially correlating the luminescence arising from the MQW exciton recombination (950 nm) with the longer wavelength (1000-1200 nm) luminescence arising from the defect-induced recombination, it is demonstrated that it is possible to determine the regions of highest film quality in both the mesa and valley regions. The present approach enables a judicious determination of the optimal regions to be used for active pixels in InGaAs/GaAs spatial light modulators.

Fabrication and characterization of sub-micron scale hall devices from 2-dimensional electron gas at the heterostrutcure of GaAs/AlGaAs

NASA Astrophysics Data System (ADS)

Keswani, Neeti; Nakajima, Yoshikata; Chauhan, Neha; Kumar, Sakthi; Ohno, H.; Das, Pintu

2018-05-01

In this work, we report the fabrication and transport properties of sub-micron Hall devices to be used for nanomagnetic studies. Hall bars were fabricated using electron-beam lithography followed by wet etching of GaAs/AlGaAs heterostructures containing two-dimensional electron gas (2-DEG). Metallization using multiple metallic layers were used to achieve ohmic contacts with the 2-DEG which is about 240 nm below the surface. Detailed characterization of the metallic layers using X-ray Photoelectron Spectroscopy (XPS) demonstrate the role of alloy formation and diffusion to form ohmic contacts with the 2-DEG. Electronic transport measurements show the metallic character of the 2-DEG. Hall effect and magnetoresistance were measured to estimate the carrier mobility of 4.2×104 cm2/V-s at 5 K in dark.

In-situ, Gate Bias Dependent Study of Neutron Irradiation Effects on AlGaN/GaN HFETs

DTIC Science & Technology

2010-03-01

band gap and high breakdown field, AlGaN devices can operate at very high temperature and operating frequency. AlGaN/GaN based structures, have been...stable under ambient conditions [3]. GaN has a wide, direct band gap of 3.4 eV. It is therefore suitable for high temperature devices. Its high...also be grown with a wurtzite crystal structure and has a band - gap of 6.1 eV. Aluminum, due to having smaller atoms than gallium, forms a smaller

Flat panel displays in the helmet-mounted display

NASA Astrophysics Data System (ADS)

Bartlett, Christopher T.; Freeman, Jonathan P.

2002-08-01

The Helmet Mounted Display has been in development for over 25 years and with few exceptions those systems in service have incorporated a miniature Cathode Ray Tube as the display source. The exceptions have been the use of Light Emitting Diodes in Helmet Sighting displays. The argument for Flat Panel Displays has been well rehearsed and this paper provides a summary of the available technologies but with a rationale for a decision to use Reflective Liquid Crystal devices. The Paper then describes sources of illumination and derives the luminance required from that source.

Contrast Transmission In Medical Image Display

NASA Astrophysics Data System (ADS)

Pizer, Stephen M.; Zimmerman, John B.; Johnston, R. Eugene

1982-11-01

The display of medical images involves transforming recorded intensities such at CT numbers into perceivable intensities such as combinations of color and luminance. For the viewer to extract the most information about patterns of decreasing and increasing recorded intensity, the display designer must pay attention to three issues: 1) choice of display scale, including its discretization; 2) correction for variations in contrast sensitivity across the display scale due to the observer and the display device (producing an honest display); and 3) contrast enhancement based on the information in the recorded image and its importance, determined by viewing objectives. This paper will present concepts and approaches in all three of these areas. In choosing display scales three properties are important: sensitivity, associability, and naturalness of order. The unit of just noticeable difference (jnd) will be carefully defined. An observer experiment to measure the jnd values across a display scale will be specified. The overall sensitivity provided by a scale as measured in jnd's gives a measure of sensitivity called the perceived dynamic range (PDR). Methods for determining the PDR fran the aforementioned PDR values, and PDR's for various grey and pseudocolor scales will be presented. Methods of achieving sensitivity while retaining associability and naturalness of order with pseudocolor scales will be suggested. For any display device and scale it is useful to compensate for the device and observer by preceding the device with an intensity mapping (lookup table) chosen so that perceived intensity is linear with display-driving intensity. This mapping can be determined from the aforementioned jnd values. With a linearized display it is possible to standardize display devices so that the same image displayed on different devices or scales (e.g. video and hard copy) will be in sane sense perceptually equivalent. Furthermore, with a linearized display, it is possible to

Device considerations and characterizations of pre and post fabricated GaAs based pHEMTs using multilayer 3D MMIC technology

NASA Astrophysics Data System (ADS)

Alim, Mohammad A.; Ali, Mayahsa M.; Haris, Norshakila; Kyabaggu, Peter B. K.; Rezazadeh, Ali A.

2017-05-01

This study focuses on the characterization of two 0.5 μm gate-length double heterojunction AlGaAs/InGaAs/GaAs pHEMTs using pre and post fabricated vertical oriented multilayer 3D monolithic microwave integrated (MMIC) circuit technology. The effects of the presence of 3D components above the active layer were accomplished by means of capacitance-voltage measurement, on-wafer DC and S-parameter measurements and two-tone intermodulation distortion measurement. The barrier height, donor concentration in the barrier layer, existing two-dimensional electron gas, output current, off and on state leakage, transconductance, cut-off frequency, small signal model parameters, gain, minimum noise figures and nonlinear distortion behavior reveals no significant performance degradation. Furthermore the fundamental device properties such as the depletion depth d, the sheet charge densities of the 2-DEG, n s, filed dependent mobility, μ, and the effective carrier velocity, v eff is not much affected due to multilayer processing. Less than 5% changes in magnitude of the device parameters are realized between the pre and post fabricated multilayer 3D MMIC technology. These effective comparisons of the both device are useful for future designs and optimizations of multilayer vertical stacked 3D MMICs.

Studies on hand-held visual communication device for the deaf and speech-impaired I. Visual display window size.

PubMed

Thurlow, W R

1980-01-01

Messages were presented which moved from right to left along an electronic alphabetic display which was varied in "window" size from 4 through 32 letter spaces. Deaf subjects signed the messages they perceived. Relatively few errors were made even at the highest rate of presentation, which corresponded to a typing rate of 60 words/min. It is concluded that many deaf persons can make effective use of a small visual display. A reduced cost is then possible for visual communication instruments for these people through reduced display size. Deaf subjects who can profit from a small display can be located by a sentence test administered by tape recorder which drives the display of the communication device by means of the standard code of the deaf teletype network.

100-period InGaAsP/InGaP superlattice solar cell with sub-bandgap quantum efficiency approaching 80%

DOE PAGES

Sayed, Islam E. H.; Jain, Nikhil; Steiner, Myles A.; ...

2017-08-25

Here, InGaAsP/InGaP quantum well (QW) structures are promising materials for next generation photovoltaic devices because of their tunable bandgap (1.50-1.80 eV) and being aluminum-free. However, the strain-balance limitations have previously limited light absorption in the QW region and constrained the external quantum efficiency (EQE) values beyond the In 0.49Ga 0.51P band-edge to less than 25%. In this work, we show that implementing a hundred period lattice matched InGaAsP/InGaP superlattice solar cell with more than 65% absorbing InGaAsP well resulted in more than 2x improvement in EQE values than previously reported strain balanced approaches. In addition, processing the devices with amore » rear optical reflector resulted in strong Fabry-Perot resonance oscillations and the EQE values were highly improved in the vicinity of these peaks, resulting in a short circuit current improvement of 10% relative to devices with a rear optical filter. These enhancements have resulted in an InGaAsP/InGaP superlattice solar cell with improved peak sub-bandgap EQE values exceeding 75% at 700 nm, an improvement in the short circuit current of 26% relative to standard InGaP devices, and an enhanced bandgap-voltage offset (W oc) of 0.4 V.« less

Recrystallization method to selenization of thin-film Cu(In,Ga)Se.sub.2 for semiconductor device applications

DOEpatents

Albin, David S.; Carapella, Jeffrey J.; Tuttle, John R.; Contreras, Miguel A.; Gabor, Andrew M.; Noufi, Rommel; Tennant, Andrew L.

1995-07-25

A process for fabricating slightly Cu-poor thin-films of Cu(In,Ga)Se.sub.2 on a substrate for semiconductor device applications includes the steps of forming initially a slightly Cu-rich, phase separated, mixture of Cu(In,Ga)Se.sub.2 :Cu.sub.x Se on the substrate in solid form followed by exposure of the Cu(In,Ga)Se.sub.2 :Cu.sub.x Se solid mixture to an overpressure of Se vapor and (In,Ga) vapor for deposition on the Cu(In,Ga)Se.sub.2 :Cu.sub.x Se solid mixture while simultaneously increasing the temperature of the solid mixture toward a recrystallization temperature (about 550.degree. C.) at which Cu(In,Ga)Se.sub.2 is solid and Cu.sub.x Se is liquid. The (In,Ga) flux is terminated while the Se overpressure flux and the recrystallization temperature are maintained to recrystallize the Cu.sub.x Se with the (In, Ga) that was deposited during the temperature transition and with the Se vapor to form the thin-film of slightly Cu-poor Cu.sub.x (In,Ga).sub.y Se.sub.z. The initial Cu-rich, phase separated large grain mixture of Cu(In,Ga)Se.sub.2 :Cu.sub.x Se can be made by sequentially depositing or co-depositing the metal precursors, Cu and (In, Ga), on the substrate at room temperature, ramping up the thin-film temperature in the presence of Se overpressure to a moderate anneal temperature (about 450.degree. C.) and holding that temperature and the Se overpressure for an annealing period. A nonselenizing, low temperature anneal at about 100.degree. C. can also be used to homogenize the precursors on the substrates before the selenizing, moderate temperature anneal.

GaN metal-oxide-semiconductor field-effect transistors on AlGaN/GaN heterostructure with recessed gate

NASA Astrophysics Data System (ADS)

Wang, Qingpeng; Ao, Jin-Ping; Wang, Pangpang; Jiang, Ying; Li, Liuan; Kawaharada, Kazuya; Liu, Yang

2015-04-01

GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with a recess gate were fabricated and characterized. The device showed good pinch-off characteristics and a maximum field-effect mobility of 145.2 cm2·V-1·s-1. The effects of etching gas of Cl2 and SiCl4 were investigated in the gate recess process. SiCl4-etched devices showed higher channel mobility and lower threshold voltage. Atomic force microscope measurement was done to investigate the etching profile with different etching protection mask. Compared with photoresist, SiO2-masked sample showed lower surface roughness and better profile with stepper sidewall and weaker trenching effect resulting in higher channel mobility in the MOSFET.

Role of AlGaN/GaN interface traps on negative threshold voltage shift in AlGaN/GaN HEMT

NASA Astrophysics Data System (ADS)

Malik, Amit; Sharma, Chandan; Laishram, Robert; Bag, Rajesh Kumar; Rawal, Dipendra Singh; Vinayak, Seema; Sharma, Rajesh Kumar

2018-04-01

This article reports negative shift in the threshold-voltage in AlGaN/GaN high electron mobility transistor (HEMT) with application of reverse gate bias stress. The device is biased in strong pinch-off and low drain to source voltage condition for a fixed time duration (reverse gate bias stress), followed by measurement of transfer characteristics. Negative threshold voltage shift after application of reverse gate bias stress indicates the presence of more carriers in channel as compared to the unstressed condition. We propose the presence of AlGaN/GaN interface states to be the reason of negative threshold voltage shift, and developed a process to electrically characterize AlGaN/GaN interface states. We verified the results with Technology Computer Aided Design (TCAD) ATLAS simulation and got a good match with experimental measurements.

Image quality degradation by light-scattering processes in high-performance display devices for medical imaging

NASA Astrophysics Data System (ADS)

Badano, Aldo

1999-11-01

This thesis addresses the characterization of light scattering processes that degrade image quality in high performance electronic display devices for digital radiography. Using novel experimental and computational tools, we study the lateral diffusion of light in emissive display devices that causes extensive veiling glare and significant reduction of the physical contrast. In addition, we examine the deleterious effects of ambient light reflections that affect the contrast of low luminance regions, and superimpose unwanted structured signal. The analysis begins by introducing the performance limitations of the human visual system to define high fidelity requirements. It is noted that current devices severely suffer from image quality degradation due to optical transport processes. To model the veiling glare and reflectance characteristics of display devices, we introduce a Monte Carlo light transport simulation code, DETECT-II, that tracks individual photons through multiple scattering events. The simulation accounts for the photon polarization state at each scattering event, and provides descriptions for rough surfaces and thin film coatings. A new experimental method to measure veiling glare is described next, based on a conic collimated probe that minimizes contamination from bright areas. The measured veiling glare ratio is taken to be the luminance in the surrounding bright field divided by the luminance in the dark circle. We show that veiling glare ratios in the order of a few hundreds can be measured with an uncertainty of a few percent. The veiling glare response function is obtained by measuring the small spot contrast ratio of test patterns having varying dark spot radius. Using DETECT-II, we then estimate the ring response functions for a high performance medical imaging monitor of current design, and compare the predictions of the model with the experimentally measured response function. The data presented in this thesis demonstrate that although

Microwave GaAs Integrated Circuits On Quartz Substrates

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

1994-01-01

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

LEC GaAs for integrated circuit applications

NASA Technical Reports Server (NTRS)

Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

1984-01-01

Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

Biocorrosion investigation of two shape memory nickel based alloys: Ni-Mn-Ga and thin film NiTi.

PubMed

Stepan, L L; Levi, D S; Gans, E; Mohanchandra, K P; Ujihara, M; Carman, G P

2007-09-01

Thin film nitinol and single crystal Ni-Mn-Ga represent two new shape memory materials with potential to be used as percutaneously placed implant devices. However, the biocompatibility of these materials has not been adequately assessed. Immersion tests were conducted on both thin film nitinol and single crystal Ni-Mn-Ga in Hank's balanced salt solution at 37 degrees C and pH 7.4. After 12 h, large pits were found on the Ni-Mn-Ga samples while thin film nitinol displayed no signs of corrosion. Further electrochemical tests on thin film nitinol samples revealed breakdown potentials superior to a mechanically polished nitinol disc. These results suggest that passivation or electropolishing of thin film nitinol maybe unnecessary to promote corrosion resistance.

Improvement of UV electroluminescence of n-ZnO/p-GaN heterojunction LED by ZnS interlayer.

PubMed

Zhang, Lichun; Li, Qingshan; Shang, Liang; Wang, Feifei; Qu, Chong; Zhao, Fengzhou

2013-07-15

n-ZnO/p-GaN heterojunction light emitting diodes with different interfacial layers were fabricated by pulsed laser deposition. The electroluminescence (EL) spectra of the n-ZnO/p-GaN diodes display a broad blue-violet emission centered at 430 nm, whereas the n-ZnO/ZnS/p-GaN and n-ZnO/AlN/p-GaN devices exhibit ultraviolet (UV) emission. Compared with the AlN interlayer, which is blocking both electron and hole at hetero-interface, the utilization of ZnS as intermediate layer can lower the barrier height for holes and keep an effective blocking for electron. Thus, an improved UV EL intensity and a low turn-on voltage (~5V) were obtained. The results were studied by peak-deconvolution with Gaussian functions and were discussed using the band diagram of heterojunctions.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

2018-03-01

We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p-i-n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

Electrical characteristics of proton-irradiated Sc2O3 passivated AlGaN/GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Luo, B.; Kim, Jihyun; Ren, F.; Gillespie, J. K.; Fitch, R. C.; Sewell, J.; Dettmer, R.; Via, G. D.; Crespo, A.; Jenkins, T. J.; Gila, B. P.; Onstine, A. H.; Allums, K. K.; Abernathy, C. R.; Pearton, S. J.; Dwivedi, R.; Fogarty, T. N.; Wilkins, R.

2003-03-01

Sc2O3-passivated AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated with 40 MeV protons to a fluence corresponding to approximately 10 years in low-earth orbit (5×109 cm-2). Devices with an AlGaN cap layer showed less degradation in dc characteristics than comparable GaN-cap devices, consistent with differences in average band energy. The changes in device performance could be attributed completely to bulk trapping effects, demonstrating that the effectiveness of the Sc2O3 layers in passivating surface states in the drain-source region was undiminished by the proton irradiation. Sc2O3-passivated AlGaN/HEMTs appear to be attractive candidates for space and terrestrial applications where resistance to high fluxes of ionizing radiation is a criteria.

Experimental evaluation of the optical quality of DMD SLM for its application as Fourier holograms displaying device

NASA Astrophysics Data System (ADS)

Molodtsov, D. Y.; Cheremkhin, P. A.; Krasnov, V. V.; Rodin, V. G.

2016-04-01

In this paper, the optical quality of micromirror DMD spatial light modulator (SLM) is evaluated and its applicability as an output device for holographic filters in dispersive correlators is analyzed. The possibility of using of DMD SLM extracted from consumer DLP-projector was experimentally evaluated by displaying of Fourier holograms. Software for displaying of holograms was developed. Experiments on holograms reconstruction was conducted with a different number of holograms pixels (and different placement on SLM). Reduction of number of pixels of output hologram (i.e. size of minimum resolvable element) led to improvement of reconstructed image quality. The evaluation shows that not every DMD-chip has acceptable optical quality for its application as display device for Fourier holograms. It was determined that major factor of reconstructed image quality degradation is a curvature of surface of SLM or its safety glass. Ranging hologram size allowed to estimate approximate size of sufficiently flat area of SLM matrix. For tested SLM it was about 1.5 mm. Further hologram size increase led to significant reconstructed image quality degradation. Developed and applied a technique allows to quickly estimate maximum size of holograms that can be displayed with specific SLM without significant degradation of reconstructed image. Additionally it allows to identify areas on the SLM with increased curvature of the surface.

Research progress of infrared detecting and display integrated device based on infrared-visible up-conversion technology

NASA Astrophysics Data System (ADS)

Xu, Junfeng; Li, Weile; He, Bo; Wang, Haowei; Song, Yong; Yang, Shengyi; Ni, Guoqiang

2018-01-01

Infrared detecting and display device (IR-DDD) is a newly developed optical up-conversion device that integrates the light-emitting diode (LED) onto the infrared (IR) photo-detector, in order to convert IR light into the carriers photo-generated in detection materials and inject them into LED to emit visible light. This IR-DDD can achieve the direct up-conversion from IR ray to visible light, showing the considerable potential in night-vision application. This paper attempts a review of its working principle and current research progresses.

Polarization-Engineered Ga-Face GaN-Based Heterostructures for Normally-Off Heterostructure Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Kim, Hyeongnam; Nath, Digbijoy; Rajan, Siddharth; Lu, Wu

2013-01-01

Polarization-engineered Ga-face GaN-based heterostructures with a GaN cap layer and an AlGaN/ p-GaN back barrier have been designed for normally-off field-effect transistors (FETs). The simulation results show that an unintentionally doped GaN cap and p-GaN layer in the buffer primarily deplete electrons in the channel and the Al0.2Ga0.8N back barrier helps to pinch off the channel. Experimentally, we have demonstrated a normally-off GaN-based field-effect transistor on the designed GaN cap/Al0.3Ga0.7N/GaN channel/Al0.2Ga0.8N/ p-GaN/GaN heterostructure. A positive threshold voltage of 0.2 V and maximum transconductance of 2.6 mS/mm were achieved for 80- μm-long gate devices. The device fabrication process does not require a dry etching process for gate recessing, while highly selective etching of the GaN cap against a very thin Al0.3GaN0.7N top barrier has to be performed to create a two-dimensional electron gas for both the ohmic and access regions. A self-aligned, selective etch of the GaN cap in the access region is introduced, using the gate metal as an etch mask. The absence of gate recess etching is promising for uniform and repeatable threshold voltage control in normally-off AlGaN/GaN heterostructure FETs for power switching applications.

Single Junction InGaP/GaAs Solar Cells Grown on Si Substrates using SiGe Buffer Layers

NASA Technical Reports Server (NTRS)

Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.

2002-01-01

Single junction InGaP/GaAs solar cells displaying high efficiency and record high open circuit voltage values have been grown by metalorganic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open circuit voltages as high as 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge-related sub-cell photoresponse. Current AM0 efficiencies of close to 16% have been measured for a large number of small area cells, whose performance is limited by non-fundamental current losses due to significant surface reflection resulting from greater than 10% front surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 nanosecond minority carrier lifetime that results from complete elimination of anti-phase domains and maintaining a threading dislocation density of approximately 8 x 10(exp 5) per square centimeter, 19-20% AM0 single junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger area cells, with identical open circuit voltages and higher short circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large area scaling is possible in the near term. Comparison to a simple model indicates that the voltage output of these GaAs on Si cells follows ideal behavior expected for lattice mismatched devices, demonstrating that unaccounted for defects and issues that have plagued other methods to epitaxially integrate III-V cells with Si are resolved using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high efficiency, lightweight and strong III-V solar cells.

GaAs Photovoltaics on Polycrystalline Ge Substrates

NASA Technical Reports Server (NTRS)

Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

2007-01-01

High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

Band-Bending of Ga-Polar GaN Interfaced with Al2O3 through Ultraviolet/Ozone Treatment.

PubMed

Kim, Kwangeun; Ryu, Jae Ha; Kim, Jisoo; Cho, Sang June; Liu, Dong; Park, Jeongpil; Lee, In-Kyu; Moody, Baxter; Zhou, Weidong; Albrecht, John; Ma, Zhenqiang

2017-05-24

Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O 3 ) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) Al 2 O 3 coated Ga-polar GaN were studied. The UV/O 3 treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the Al 2 O 3 /GaN interfaces. The UV/O 3 treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of Al 2 O 3 deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O 3 treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the Al 2 O 3 /GaN interfaces. An optimal UV/O 3 treatment condition also exists for realizing the "best" interface conditions. The study of UV/O 3 treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.

Tungsten as a Chemically-Stable Electrode Material on Ga-Containing Piezoelectric Substrates Langasite and Catangasite for High-Temperature SAW Devices

PubMed Central

Rane, Gayatri K.; Seifert, Marietta; Menzel, Siegfried; Gemming, Thomas; Eckert, Jürgen

2016-01-01

Thin films of tungsten on piezoelectric substrates La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) have been investigated as a potential new electrode material for interdigital transducers for surface acoustic wave-based sensor devices operating at high temperatures up to 800 °C under vacuum conditions. Although LGS is considered to be suitable for high-temperature applications, it undergoes chemical and structural transformation upon vacuum annealing due to diffusion of gallium and oxygen. This can alter the device properties depending on the electrode nature, the annealing temperature, and the duration of the application. Our studies present evidence for the chemical stability of W on these substrates against the diffusion of Ga/O from the substrate into the film, even upon annealing up to 800 °C under vacuum conditions using Auger electron spectroscopy and energy-dispersive X-ray spectroscopy, along with local studies using transmission electron microscopy. Additionally, the use of CTGS as a more stable substrate for such applications is indicated. PMID:28787898

Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Alfieri, G.; Sundaramoorthy, V. K.; Micheletto, R.

2018-05-01

Magnesium (Mg) is the p-type doping of choice for GaN, and selective area doping by ion implantation is a routine technique employed during device processing. While electrically active defects have been thoroughly studied in as-grown GaN, not much is known about defects generated by ion implantation. This is especially true for the case of Mg. In this study, we carried out an electrical characterization investigation of point defects generated by Mg implantation in GaN. We have found at least nine electrically active levels in the 0.2-1.2 eV energy range, below the conduction band. The isochronal annealing behavior of these levels showed that most of them are thermally stable up to 1000 °C. The nature of the detected defects is then discussed in the light of the results found in the literature.

Asymmetrical design for non-relaxed near-UV AlGaN/GaN distributed Bragg reflectors

NASA Astrophysics Data System (ADS)

Moudakir, T.; Abid, M.; Doan, B.-T.; Demarly, E.; Gautier, S.; Orsal, G.; Jacquet, J.; Ougazzaden, A.; Genty, F.

2010-10-01

Towards the development of high efficient GaN-based Vertical Cavity devices, the fabrication of cracks-free high reflective semiconductor mirrors is still an issue. For near-UV operating devices, one of the best solution is the use of AlGaN/GaN materials family. With a relatively high Al molar fraction in AlGaN, a large enough index contrast can be achieved to fabricate high reflectivity mirrors. However, the lattice mismatch between AlGaN and GaN increases with the Al molar fraction and induces a lot of cracks in the structure which affect its optical and electrical properties. Moreover, for a regrowth of an active layer on the top of the mirror, it is necessary to suppress crack generations to achieve a smooth surface. In this work, asymmetrical designs were investigated for the modeling of fully-strained AlGaN/GaN distributed Bragg Reflectors with crack-free surfaces. First, the critical thickness of MOVPE-grown AlGaN on GaN-on-sapphire templates was experimentally determined and modeled. Then, several AlGaN/GaN mirrors with various Al molar fractions and asymmetry factors were simulated demonstrating that non relaxed DBRs could be obtained with adequate parameters. Finally, it has also been shown that there is a best suited Al molar fraction in AlGaN for each DBR centering wavelength.

Video display engineering and optimization system

NASA Technical Reports Server (NTRS)

Larimer, James (Inventor)

1997-01-01

A video display engineering and optimization CAD simulation system for designing a LCD display integrates models of a display device circuit, electro-optics, surface geometry, and physiological optics to model the system performance of a display. This CAD system permits system performance and design trade-offs to be evaluated without constructing a physical prototype of the device. The systems includes a series of modules which permit analysis of design trade-offs in terms of their visual impact on a viewer looking at a display.

Analysis of Time Dependent Electric Field Degradation in AlGaN/GaN HEMTs (POSTPRINT)

DTIC Science & Technology

2014-10-01

identifying and understanding the failure mechanisms that limit the safe operating area of GaN HEMTs. 15. SUBJECT TERMS aluminum gallium nitride... gallium nitride, HEMTs, semiconductor device reliability, transistors 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER...area of GaN HEMTs. Index Terms— Aluminum gallium nitride, gallium nitride, HEMTs, semiconductor device reliability, transistors. I. INTRODUCTION A

Defects and annealing studies in 1-Me electron irradiated (AlGa)As-GaAs solar cells

NASA Technical Reports Server (NTRS)

Li, S. S.; Wang, W. L.; Loo, R. Y.; Rahilly, W. P.

1982-01-01

The deep-level defects and recombination mechanisms in the one-MeV electron irradiated (AlGa)As-GaAs solar cells under various irradiation and annealing conditions are discussed. Deep-level transient spectroscopy (DLTS) and capacitance-voltage (CV) techniques were used to determine the defect and recombination parameters such as energy levels and defect density, carrier capture cross sections and lifetimes for both electron and hole traps as well as hole diffusion lengths in these electron irradiated GaAs solar cells. GaAs solar cells used in this study were prepared by the infinite solution melt liquid phase epitaxial (LPE) technique at Hughes Research Lab., with (Al0.9Ga0.1)-As window layer, Be-diffused p-GaAs layer on Sn-doped n-GaAs or undoped n-GaAs active layer grown on n(+)-GaAs substrate. Mesa structure with area of 5.86x1000 sq cm was fabricated. Three different irradiation and annealing experiments were performed on these solar cells.

Fabrication of full-color GaN-based light-emitting diodes on nearly lattice-matched flexible metal foils.

PubMed

Kim, Hyeryun; Ohta, Jitsuo; Ueno, Kohei; Kobayashi, Atsushi; Morita, Mari; Tokumoto, Yuki; Fujioka, Hiroshi

2017-05-18

GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.

Inverted Al0.25Ga0.75N/GaN ultraviolet p-i-n photodiodes formed on p-GaN template layer grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Chang, Kuo-Hua; Sheu, Jinn-Kong; Lee, Ming-Lun; Tu, Shang-Ju; Yang, Chih-Ciao; Kuo, Huan-Shao; Yang, J. H.; Lai, Wei-Chih

2010-07-01

Inverted Al0.25Ga0.75N/GaN ultraviolet (UV) p-i-n photodiodes (PDs) were grown by selective-area regrowth on p-GaN template. The inverted devices with low-resistivity n-type AlGaN top-contact layers exhibited a typical zero-bias peak responsivity of 66.7 mA/W at 310 nm corresponding to the external quantum efficiency of 26.6%. The typical UV-to-visible (310/400 nm) spectral rejection ratio at zero-bias was over three orders of magnitude. The differential resistance and detectivity were obtained at approximately 6.2×1012 Ω and 3.4×1013 cm Hz1/2 W-1, respectively. Compared with conventional AlGaN/GaN-based UV p-i-n PDs, the proposed device structure can potentially achieve solar-blind AlGaN/GaN-based p-i-n PDs with low-aluminum content or aluminum-free p-contact layer and reduce excessive tensile strain due to the lattice mismatch between AlGaN and GaN layers.

An AlGaN/GaN high-electron-mobility transistor with an AlN sub-buffer layer

NASA Astrophysics Data System (ADS)

Shealy, J. R.; Kaper, V.; Tilak, V.; Prunty, T.; Smart, J. A.; Green, B.; Eastman, L. F.

2002-04-01

The AlGaN/GaN high-electron-mobility transistor requires a thermally conducting, semi-insulating substrate to achieve the best possible microwave performance. The semi-insulating SiC substrate is currently the best choice for this device technology; however, fringing fields which penetrate the GaN buffer layer at pinch-off introduce significant substrate conduction at modest drain bias if channel electrons are not well confined to the nitride structure. The addition of an insulating AlN sub-buffer on the semi-insulating SiC substrate suppresses this parasitic conduction, which results in dramatic improvements in the AlGaN/GaN transistor performance. A pronounced reduction in both the gate-lag and the gate-leakage current are observed for structures with the AlN sub-buffer layer. These structures operate up to 50 V drain bias under drive, corresponding to a peak voltage of 80 V, for a 0.30 µm gate length device. The devices have achieved high-efficiency operation at 10 GHz (>70% power-added efficiency in class AB mode at 15 V drain bias) and the highest output power density observed thus far (11.2 W mm-1). Large-periphery devices (1.5 mm gate width) deliver 10 W (continuous wave) of maximum saturated output power at 10 GHz. The growth, processing, and performance of these devices are briefly reviewed.

InGaAsN/GaAs Heterostructures for Long-Wavelength Light-Emitting Devices

DTIC Science & Technology

2000-06-23

vertical cavity surface emitting lasers ( VCSELs ) on GaAs is expected to be possible by... molecular beam epitaxy using an RF plasma-source. Broad area and ridge waveguide laser structures based on such QWs exhibit performance that can...work with GaAs/AlAs DBR-mirrors is expected to lead to novel vertical cavity lasers for optical fiber communication systems. Acknowledgement

Nanoscale characterization of GaN/InGaN multiple quantum wells on GaN nanorods by photoluminescence spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Weijian; Wen, Xiaoming; Latzel, Michael; Yang, Jianfeng; Huang, Shujuan; Shrestha, Santosh; Patterson, Robert; Christiansen, Silke; Conibeer, Gavin

2017-02-01

GaN/InGaN multiple quantum wells (MQW) and GaN nanorods have been widely studied as a candidate material for high-performance light emitting diodes. In this study, GaN/InGaN MQW on top of GaN nanorods are characterized in nanoscale using confocal microscopy associated with photoluminescence spectroscopy, including steady-state PL, timeresolved PL and fluorescence lifetime imaging (FLIM). Nanorods are fabricated by etching planar GaN/InGaN MQWs on top of a GaN layer on a c-plane sapphire substrate. Photoluminescence efficiency from the GaN/InGaN nanorods is evidently higher than that of the planar structure, indicating the emission improvement. Time-resolved photoluminescence (TRPL) prove that surface defects on GaN nanorod sidewalls have a strong influence on the luminescence property of the GaN/InGaN MWQs. Such surface defects can be eliminated by proper surface passivation. Moreover, densely packed nanorod array and sparsely standing nanorods have been studied for better understanding the individual property and collective effects from adjacent nanorods. The combination of the optical characterization techniques guides optoelectronic materials and device fabrication.

Damage free Ar ion plasma surface treatment on In{sub 0.53}Ga{sub 0.47}As-on-silicon metal-oxide-semiconductor device

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

Koh, Donghyi; Shin, Seung Heon; Ahn, Jaehyun

2015-11-02

In this paper, we investigated the effect of in-situ Ar ion plasma surface pre-treatment in order to improve the interface properties of In{sub 0.53}Ga{sub 0.47}As for high-κ top-gate oxide deposition. X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor capacitors (MOSCAPs) demonstrate that Ar ion treatment removes the native oxide on In{sub 0.53}Ga{sub 0.47}As. The XPS spectra of Ar treated In{sub 0.53}Ga{sub 0.47}As show a decrease in the AsO{sub x} and GaO{sub x} signal intensities, and the MOSCAPs show higher accumulation capacitance (C{sub acc}), along with reduced frequency dispersion. In addition, Ar treatment is found to suppress the interface trap density (D{sub it}),more » which thereby led to a reduction in the threshold voltage (V{sub th}) degradation during constant voltage stress and relaxation. These results outline the potential of surface treatment for III-V channel metal-oxide-semiconductor devices and application to non-planar device process.« less

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

1998-01-01

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

GaInP2/GaAs tandem cells for space applications

NASA Technical Reports Server (NTRS)

Olson, J. M.; Kurtz, S. R.; Kibbler, A. E.; Bertness, K. A.; Friedman, D. J.

1991-01-01

The monolithic, tunnel-junction-interconnected tandem combination of a GaInP2 top cell and a GaAs bottom cell has achieved a one-sun, AM1.5 efficiency of 27.3 percent. With proper design of the top cell, air mass zero (AM0) efficiencies greater than 25 percent are possible. A description and the advantages of this device for space applications are presented and discussed. The advantages include high-voltage, low-current, two-terminal operation for simple panel fabrication, and high conversion efficiency with low-temperature coefficient. Also, because the active regions of the device are Al-free, the growth of high efficiency devices is not affected by trace levels of O2 or H2O in the MOCVD growth system.

Metasurface integrated high energy efficient and high linearly polarized InGaN/GaN light emitting diode.

PubMed

Wang, Miao; Xu, Fuyang; Lin, Yu; Cao, Bing; Chen, Linghua; Wang, Chinhua; Wang, Jianfeng; Xu, Ke

2017-07-06

We proposed and demonstrated an integrated high energy efficient and high linearly polarized InGaN/GaN green LED grown on (0001) oriented sapphire with combined metasurface polarizing converter and polarizer system. It is different from those conventional polarized light emissions generated with plasmonic metallic grating in which at least 50% high energy loss occurs inherently due to high reflection of the transverse electric (TE) component of an electric field. A reflecting metasurface, with a two dimensional elliptic metal cylinder array (EMCA) that functions as a half-wave plate, was integrated at the bottom of a LED such that the back-reflected TE component, that is otherwise lost by a dielectric/metal bi-layered wire grids (DMBiWG) polarizer on the top emitting surface of the LED, can be converted to desired transverse magnetic (TM) polarized emission after reflecting from the metasurface. This significantly enhances the polarized light emission efficiency. Experimental results show that extraction efficiency of the polarized emission can be increased by 40% on average in a wide angle of ±60° compared to that with the naked bottom of sapphire substrate, or 20% compared to reflecting Al film on the bottom of a sapphire substrate. An extinction ratio (ER) of average value 20 dB within an angle of ±60° can be simultaneously obtained directly from an InGaN/GaN LED. Our results show the possibility of simultaneously achieving a high degree of polarization and high polarization extraction efficiency at the integrated device level. This advances the field of GaN LED toward energy efficiency, multi-functional applications in illumination, display, medicine, and light manipulation.

Design of high-efficiency, radiation-hard, GaInP/GaAs solar cells

NASA Technical Reports Server (NTRS)

Kurtz, Sarah R.; Bertness, K. A.; Kibbler, A. E.; Kramer, C.; Olson, J. M.

1994-01-01

In recently years, Ga(0.5)In((0.5)P/GaAs cells have drawn increased attention both because of their high efficiencies and because they are well suited for space applications. They can be grown and processed as two-junction devices with roughly twice the voltage and half the current of GaAs cells. They have low temperature coefficients, and have good potential for radiation hardness. We have previously reported the effects of electron irradiation on test cells which were not optimally designed for space. From those results we estimated that an optimally designed cell could achieve 20 percent after irradiation with 10(exp 15) cm(exp -2) 1 MeV electrons. Modeling studies predicted that slightly higher efficiencies may be achievable. Record efficiencies for EOL performance of other types of cells are significantly lower. Even the best Si and InP cells have BOL efficiencies lower than the EOL efficiency we report here. Good GaAs cells have an EOL efficiency of 16 percent. The InP/Ga(0.5)In(0.5)As two-junction, two-terminal device has a BOL efficiency as high as 22.2 percent, but radiation results for these cells were limited. In this study we use the previous modeling and irradiation results to design a set of Ga(0.5)In(0.5)P/GaAs cells that will demonstrate the importance of the design parameters and result in high-efficiency devices. We report record AMO efficiencies: a BOL efficiency of 25.7 percent for a device optimized for BOL performance and two of different designs with EOL efficiencies of 19.6 percent (at 10(exp 15) cm(exp -2) 1MeV electrons). We vary the bottom-cell base doping and the top-cell thickness to show the effects of these two important design parameters. We get an unexpected result indicating that the dopant added to the bottom-cell base also increases the degradation of the top cell.

Distributed feedback InGaN/GaN laser diodes

NASA Astrophysics Data System (ADS)

Slight, Thomas J.; Watson, Scott; Yadav, Amit; Grzanka, Szymon; Stanczyk, Szymon; Docherty, Kevin E.; Rafailov, Edik; Perlin, Piotr; Najda, Steve; Leszczyński, Mike; Kelly, Anthony E.

2018-02-01

We have realised InGaN/GaN distributed feedback laser diodes emitting at a single wavelength in the 42X nm wavelength range. Laser diodes based on Gallium Nitride (GaN) are useful devices in a wide range of applications including atomic spectroscopy, data storage and optical communications. To fully exploit some of these application areas there is a need for a GaN laser diode with high spectral purity, e.g. in atomic clocks, where a narrow line width blue laser source can be used to target the atomic cooling transition. Previously, GaN DFB lasers have been realised using buried or surface gratings. Buried gratings require complex overgrowth steps which can introduce epi-defects. Surface gratings designs, can compromise the quality of the p-type contact due to dry etch damage and are prone to increased optical losses in the grating regions. In our approach the grating is etched into the sidewall of the ridge. Advantages include a simpler fabrication route and design freedom over the grating coupling strength.Our intended application for these devices is cooling of the Sr+ ion and for this objective the laser characteristics of SMSR, linewidth, and power are critical. We investigate how these characteristics are affected by adjusting laser design parameters such as grating coupling coefficient and cavity length.

Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor

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

MacLeod, S. J.; See, A. M.; Keane, Z. K.

2014-01-06

Radio frequency reflectometry is demonstrated in a sub-micron undoped AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive candidates to study single electron phenomena, due to their charge stability and robust electronic properties after thermal cycling. However, these devices require a large top-gate, which is unsuitable for the fast and sensitive radio frequency reflectometry technique. Here, we demonstrate that rf reflectometry is possible in an undoped SET.

SEMICONDUCTOR DEVICES: A Ga-doped ZnO transparent conduct layer for GaN-based LEDs

NASA Astrophysics Data System (ADS)

Zhen, Liu; Xiaofeng, Wang; Hua, Yang; Yao, Duan; Yiping, Zeng

2010-09-01

An 8 μm thick Ga-doped ZnO (GZO) film grown by metal-source vapor phase epitaxy was deposited on a GaN-based light-emitting diode (LED) to substitute for the conventional ITO as a transparent conduct layer (TCL). Electroluminescence spectra exhibited that the intensity value of LED emission with a GZO TCL is markedly improved by 23.6% as compared to an LED with an ITO TCL at 20 mA. In addition, the forward voltage of the LED with a GZO TCL at 20 mA is higher than that of the conventional LED. To investigate the reason for the increase of the forward voltage, X-ray photoelectron spectroscopy was performed to analyze the interface properties of the GZO/p-GaN heterojunction. The large valence band offset (2:24 ± 0:21 eV) resulting from the formation of Ga2O3 in the GZO/p-GaN interface was attributed to the increase of the forward voltage.

Television, computer and portable display device use by people with central vision impairment

PubMed Central

Woods, Russell L; Satgunam, PremNandhini

2011-01-01

Purpose To survey the viewing experience (e.g. hours watched, difficulty) and viewing metrics (e.g. distance viewed, display size) for television (TV), computers and portable visual display devices for normally-sighted (NS) and visually impaired participants. This information may guide visual rehabilitation. Methods Survey was administered either in person or in a telephone interview on 223 participants of whom 104 had low vision (LV, worse than 6/18, age 22 to 90y, 54 males), and 94 were NS (visual acuity 6/9 or better, age 20 to 86y, 50 males). Depending on their situation, NS participants answered up to 38 questions and LV participants answered up to a further 10 questions. Results Many LV participants reported at least “some” difficulty watching TV (71/103), reported at least “often” having difficulty with computer displays (40/76) and extreme difficulty watching videos on handheld devices (11/16). The average daily TV viewing was slightly, but not significantly, higher for the LV participants (3.6h) than the NS (3.0h). Only 18% of LV participants used visual aids (all optical) to watch TV. Most LV participants obtained effective magnification from a reduced viewing distance for both TV and computer display. Younger LV participants also used a larger display when compared to older LV participants to obtain increased magnification. About half of the TV viewing time occurred in the absence of a companion for both the LV and the NS participants. The mean number of TVs at home reported by LV participants (2.2) was slightly but not significantly (p=0.09) higher than NS participants (2.0). LV participants were equally likely to have a computer but were significantly (p=0.004) less likely to access the internet (73/104) compared to NS participants (82/94). Most LV participants expressed an interest in image enhancing technology for TV viewing (67/104) and for computer use (50/74), if they used a computer. Conclusion In this study, both NS and LV participants

Panoramic projection avionics displays

NASA Astrophysics Data System (ADS)

Kalmanash, Michael H.

2003-09-01

Avionics projection displays are entering production in advanced tactical aircraft. Early adopters of this technology in the avionics community used projection displays to replace or upgrade earlier units incorporating direct-view CRT or AMLCD devices. Typical motivation for these upgrades were the alleviation of performance, cost and display device availability concerns. In these systems, the upgraded (projection) displays were one-for-one form / fit replacements for the earlier units. As projection technology has matured, this situation has begun to evolve. The Lockheed-Martin F-35 is the first program in which the cockpit has been specifically designed to take advantage of one of the more unique capabilities of rear projection display technology, namely the ability to replace multiple small screens with a single large conformal viewing surface in the form of a panoramic display. Other programs are expected to follow, since the panoramic formats enable increased mission effectiveness, reduced cost and greater information transfer to the pilot. Some of the advantages and technical challenges associated with panoramic projection displays for avionics applications are described below.

ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

NASA Technical Reports Server (NTRS)

Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.

1995-01-01

A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

The effect of time in use on the display performance of the iPad.

PubMed

Caffery, Liam J; Manthey, Kenneth L; Sim, Lawrence H

2016-07-01

The aim of this study was to evaluate changes to the luminance, luminance uniformity and conformance to the digital imaging and communication in medicine greyscale standard display function (GSDF) as a function of time in use for the iPad. Luminance measurements of the American Association of Physicists in Medicine (AAPM) Group 18 task group (TG18) luminance uniformity and luminance test patterns (TG18-UNL and TG18-LN8) were performed using a calibrated near-range luminance meter. Nine sets of measurements were taken, where the time in use of the iPad ranged from 0 to 2500 h. The maximum luminance (Lmax) of the display decreased (367-338 cdm(-2)) as a function of time. The minimum luminance remained constant. The maximum non-uniformity coefficient was 11%. Luminance uniformity decreased slightly as a function of time in use. The conformance of the iPad deviated from the GSDF curve at commencement of use. Deviation did not increase as a function of time in use. This study has demonstrated that the iPad display exhibits luminance degradation typical of liquid crystal displays. The Lmax of the iPad fell below the American College of Radiology-AAPM-Society of Imaging Informatics in Medicine recommendations for primary displays (>350 cdm(-2)) at approximately 1000 h in use. The Lmax recommendation for secondary displays (>250 cdm(-2)) was exceeded during the entire study. The maximum non-uniformity coefficient did not exceed the recommendations for either primary or secondary displays. The deviation from the GSDF exceeded the recommendations of the TG18 for use as either a primary or secondary display. The brightness, uniformity and contrast response are reasonably stable over the useful lifetime of the device; however, the device fails to meet the contrast response standard for either a primary or secondary display.

GaN Initiative for Grid Applications (GIGA)

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

Turner, George

2015-07-03

For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -evenmore » for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral

Enhanced light extraction from free-standing InGaN/GaN light emitters using bio-inspired backside surface structuring.

PubMed

Pynn, Christopher D; Chan, Lesley; Lora Gonzalez, Federico; Berry, Alex; Hwang, David; Wu, Haoyang; Margalith, Tal; Morse, Daniel E; DenBaars, Steven P; Gordon, Michael J

2017-07-10

Light extraction from InGaN/GaN-based multiple-quantum-well (MQW) light emitters is enhanced using a simple, scalable, and reproducible method to create hexagonally close-packed conical nano- and micro-scale features on the backside outcoupling surface. Colloidal lithography via Langmuir-Blodgett dip-coating using silica masks (d = 170-2530 nm) and Cl 2 /N 2 -based plasma etching produced features with aspect ratios of 3:1 on devices grown on semipolar GaN substrates. InGaN/GaN MQW structures were optically pumped at 266 nm and light extraction enhancement was quantified using angle-resolved photoluminescence. A 4.8-fold overall enhancement in light extraction (9-fold at normal incidence) relative to a flat outcoupling surface was achieved using a feature pitch of 2530 nm. This performance is on par with current photoelectrochemical (PEC) nitrogen-face roughening methods, which positions the technique as a strong alternative for backside structuring of c-plane devices. Also, because colloidal lithography functions independently of GaN crystal orientation, it is applicable to semipolar and nonpolar GaN devices, for which PEC roughening is ineffective.

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

NASA Astrophysics Data System (ADS)

Cheng, Zhi-Qun; Hu, Sha; Liu, Jun; Zhang, Qi-Jun

2011-03-01

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model. Project supported by the National Natural Science Foundation of China (Grant No. 60776052).

76 FR 13432 - In the Matter of Certain Display Devices, Including Digital Televisions and Monitors II; Notice...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-11

... INTERNATIONAL TRADE COMMISSION [Inv. No. 337-TA-765] In the Matter of Certain Display Devices, Including Digital Televisions and Monitors II; Notice of Investigation AGENCY: U.S. International Trade... that a complaint was filed with the U.S. International Trade Commission on February 9, 2011, under...

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions

NASA Astrophysics Data System (ADS)

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-01

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions.

PubMed

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-25

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

I2 basal stacking fault as a degradation mechanism in reverse gate-biased AlGaN/GaN HEMTs

NASA Astrophysics Data System (ADS)

Lang, A. C.; Hart, J. L.; Wen, J. G.; Miller, D. J.; Meyer, D. J.; Taheri, M. L.

2016-09-01

Here, we present the observation of a bias-induced, degradation-enhancing defect process in plasma-assisted molecular beam epitaxy grown reverse gate-biased AlGaN/GaN high electron mobility transistors (HEMTs), which is compatible with the current theoretical framework of HEMT degradation. Specifically, we utilize both conventional transmission electron microscopy and aberration-corrected transmission electron microscopy to analyze microstructural changes in not only high strained regions in degraded AlGaN/GaN HEMTs but also the extended gate-drain access region. We find a complex defect structure containing an I2 basal stacking fault and offer a potential mechanism for device degradation based on this defect structure. This work supports the reality of multiple failure mechanisms during device operation and identifies a defect potentially involved with device degradation.

Hydraulic Universal Display Processor System (HUDPS).

DTIC Science & Technology

1981-11-21

emphasis on smart alphanumeric devices in Task II. Volatile and non-volatile memory components were utilized along with the Intel 8748 microprocessor...system. 1.2 TASK 11 Fault display methods for ground support personnel were investigated during Phase II with emphasis on smart alphanumeric devices...CONSIDERATIONS Methods of display fault indication for ground support personnel have been investigated with emphasis on " smart " alphanumeric devices

Cryogenic operation of pseudomorphic AlGaAs/InGaAs single-quantum-well MODFETs

NASA Technical Reports Server (NTRS)

Masselink, W. T.; Ketterson, A.; Klem, J.; Kopp, W.; Morkoc, H.

1985-01-01

The 77 K operation of AlGaAs/InGaAs MODFETs has been investigated. The structures, grown by MBE, make use of a 200 A undoped In(0.15)Ga(0.85)As quantum well for electron confinement and an Si-doped Al(0.15)Ga(0.85)As top barrier. The MODFETs with 1 micron gate lengths exhibit extrinsic transconductances of 360 mS/mm and maximum currents of 310 mA/mm at 77 K. The use of a low Al mole fraction AlGaAs/InGaAs heterojunction makes it possible to avoid the persistent trapping effects encountered in AlGaAs/GaAs MODFETs without sacrificing device performance.

Rib waveguide in Ga-Sb-S chalcogenide glass for on-chip mid-IR supercontinuum sources: Design and analysis

NASA Astrophysics Data System (ADS)

Saini, Than Singh; Tiwari, Umesh Kumar; Sinha, Ravindra Kumar

2017-08-01

Recently, highly nonlinear Ga-Sb-S chalcogenide glasses have been reported for promising mid-infrared applications such as thermal imaging, nonlinear optics, and infrared lasers. However, the nonlinear optical fiber and waveguide geometries in Ga-Sb-S chalcogenide glasses have not been reported to date. In this paper, we numerically investigate the design of the dual zero dispersion engineered rib waveguide in Ga8Sb32S60 chalcogenide glass by employing MgF2 glass as a lower and upper cladding material. The waveguide structure possesses nonlinearity as high as 24 100 W-1 Km-1 and 14 000 W-1 Km-1 at 2050 and 2800 nm, respectively. The reported waveguide is able to generate a mid-infrared supercontinuum spectrum spanning from 1000 to 7800 nm when it pumped with 97 femtosecond laser pulses of a peak power of 1 kW at 2050 nm. We have also showed that the supercontinuum spectrum can be extended to the spectral range of 1000-9700 nm using pumping with 497 fs pulses of a peak power of 6.4 kW at 2800 nm. To the best of our knowledge, the proposed rib waveguide structure in Ga8Sb32S60 chalcogenide glass has been reported first time for nonlinear applications. Such a dispersion engineered rib waveguide structure has potential applications for the low-cost, power efficient, and compact on-chip mid-infrared supercontinuum sources and other nonlinear photonic devices.

Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

PubMed

Sharma, N; Periasamy, C; Chaturvedi, N

2018-07-01

In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

1.3 μm VCSELs: InGaAs/GaAs, GaInNAs/GaAs multiple quantum wells, and InAs/GaAs quantum dots — three candidates as active material

NASA Astrophysics Data System (ADS)

Gilet, Ph.; Pougeoise, E.; Grenouillet, L.; Grosse, Ph.; Olivier, N.; Poncet, S.; Chelnokov, A.; Gérard, J. M.; Stevens, R.; Hamelin, R.; Hammar, M.; Berggren, J.; Sundgren, P.

2007-02-01

In this article, we report our results on 1.3μm VCSELs for optical interconnection applications. Room temperature continuous-wave lasing operation is demonstrated for top emitting oxide-confined devices with three different active materials, highly strained InGaAs/GaAs(A) and GaInNAs/GaAs (B) multiple quantum wells (MQW) or InAs/GaAs (C) quantum dots (QD). Conventional epitaxial structures grown respectively by Metal Organic Vapour Phase Epitaxy (MOVPE), Molecular Beam Epitaxy (MBE) and MBE, contain fully doped GaAs/AlGaAs DBRs. All three epilayers are processed in the same way. Current and optical confinement are realized by selective wet oxidation. Circular apertures from 2 (micron)m to 16 (micron)m diameters are defined. At room temperature and in continuous wave operation, all three systems exhibit lasing operation at wavelengths above 1 275nm and reached 1 300nm for material (A). Typical threshold currents are in the range [1- 10]mA and are strongly dependent firstly on oxide diameter and secondly on temperature. Room temperature cw maximum output power corresponds respectively to 1.77mW, 0.5mW and 0.6mW. By increasing driving current, multimode operation occurs at different level depending on the oxide diameter. In case (A), non conventional modal behaviors will be presented and explained by the presence of specific oxide modes. Thermal behaviors of the different devices have been compared. In case (A) and (C) we obtain a negative T0. We will conclude on the different active materials in terms of performances with respect to 1300nm VCSEL applications.

EMU helmet mounted display

NASA Technical Reports Server (NTRS)

Marmolejo, Jose (Inventor); Smith, Stephen (Inventor); Plough, Alan (Inventor); Clarke, Robert (Inventor); Mclean, William (Inventor); Fournier, Joseph (Inventor)

1990-01-01

A helmet mounted display device is disclosed for projecting a display on a flat combiner surface located above the line of sight where the display is produced by two independent optical channels with independent LCD image generators. The display has a fully overlapped field of view on the combiner surface and the focus can be adjusted from a near field of four feet to infinity.

LEO Flight Testing of GaAs on Si Solar Cells Aboard MISSES

NASA Technical Reports Server (NTRS)

Wilt, David M.; Clark, Eric B.; Ringel, Steven A.; Andre, Carrie L.; Smith, Mark A.; Scheiman, David A.; Jenkins, Phillip P.; Maurer, William F.; Fitzgerald, Eugene A.; Walters, R. J.

2004-01-01

Previous research efforts have demonstrated small area (0.04 cm) GaAs on Si (GaAs/Si) solar cells with AM0 efficiencies in excess of 17%. These results were achieved on Si substrates coated with a step graded buffer of Si(x),Ge(1-x) alloys graded to 100% Ge. Recently, a 100-fold increase in device area was accomplished for these devices in preparation for on-orbit testing of this technology aboard Materials International Space Station Experiment number 5 (MISSE5). The GaAs/Si MISSE5 experiment contains five (5) GaAs/Si test devices with areas of lcm(exp 2) and 4cm(exp 4) as well as two (2) GaAs on GaAs control devices. Electrical performance data, measured on-orbit for three (3) of the test devices and one (1) of the control devices, will be telemetered to ground stations daily. After approximately one year on orbit, the MISSE5 payload will be returned to Earth for post flight evaluation. This paper will discuss the development of the GaAs/Si devices for the MISSE5 flight experiment and will present recent ground and on-orbit performance data.

Analysis of reverse gate leakage mechanism of AlGaN/GaN HEMTs with N2 plasma surface treatment

NASA Astrophysics Data System (ADS)

Liu, Hui; Zhang, Zongjing; Luo, Weijun

2018-06-01

The mechanism of reverse gate leakage current of AlGaN/GaN HEMTs with two different surface treatment methods are studied by using C-V, temperature dependent I-V and theoretical analysis. At the lower reverse bias region (VR >- 3.5 V), the dominant leakage current mechanism of the device with N2 plasma surface treatment is the Poole-Frenkel emission current (PF), and Trap-Assisted Tunneling current (TAT) is the principal leakage current of the device which treated by HCl:H2O solution. At the higher reverse bias region (VR <- 3.5 V), both of the two samples show good agreement with the surface leakage mechanism. The leakage current of the device with N2 plasma surface treatment is one order of magnitude smaller than the device which treated by HCl:H2O solution. This is due to the recovery of Ga-N bond in N2 plasma surface treatment together with the reduction of the shallow traps in post-gate annealing (PGA) process. The measured results agree well with the theoretical calculations and demonstrate N2 plasma surface treatment can reduce the reverse leakage current of the AlGaN/GaN HEMTs.

Photocarrier extraction in GaAsSb/GaAsN type-II QW superlattice solar cells

NASA Astrophysics Data System (ADS)

Aeberhard, U.; Gonzalo, A.; Ulloa, J. M.

2018-05-01

Photocarrier transport and extraction in GaAsSb/GaAsN type-II quantum well superlattices are investigated by means of inelastic quantum transport calculations based on the non-equilibrium Green's function formalism. Evaluation of the local density of states and the spectral current flow enables the identification of different regimes for carrier localization, transport, and extraction as a function of configurational parameters. These include the number of periods, the thicknesses of the individual layers in one period, the built-in electric field, and the temperature of operation. The results for the carrier extraction efficiency are related to experimental data for different symmetric GaAsSb/GaAsN type-II quantum well superlattice solar cell devices and provide a qualitative explanation for the experimentally observed dependence of photovoltaic device performance on the period thickness.

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

1998-09-08

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

Wide-Bandgap Semiconductor Devices for Automotive Applications

NASA Astrophysics Data System (ADS)

Sugimoto, M.; Ueda, H.; Uesugi, T.; Kachi, T.

2007-06-01

In this paper, we discuss requirements of power devices for automotive applications, especially hybrid vehicles and the development of GaN power devices at Toyota. We fabricated AlGaN/GaN HEMTs and measured their characteristics. The maximum breakdown voltage was over 600V. The drain current with a gate width of 31mm was over 8A. A thermograph image of the HEMT under high current operation shows the AlGaN/GaN HEMT operated at more than 300°C. And we confirmed the operation of a vertical GaN device. All the results of the GaN HEMTs are really promising to realize high performance and small size inverters for future automobiles.

Modeling and optimization of a double-well double-barrier GaN/AlGaN/GaN/AlGaN resonant tunneling diode

NASA Astrophysics Data System (ADS)

Liu, Yang; Gao, Bo; Gong, Min; Shi, Ruiying

2017-06-01

The influence of a GaN layer as a sub-quantum well for an AlGaN/GaN/AlGaN double barrier resonant tunneling diode (RTD) on device performance has been investigated by means of numerical simulation. The introduction of the GaN layer as the sub-quantum well turns the dominant transport mechanism of RTD from the 3D-2D model to the 2D-2D model and increases the energy difference between tunneling energy levels. It can also lower the effective height of the emitter barrier. Consequently, the peak current and peak-to-valley current difference of RTD have been increased. The optimal GaN sub-quantum well parameters are found through analyzing the electrical performance, energy band, and transmission coefficient of RTD with different widths and depths of the GaN sub-quantum well. The most pronounced electrical parameters, a peak current density of 5800 KA/cm2, a peak-to-valley current difference of 1.466 A, and a peak-to-valley current ratio of 6.35, could be achieved by designing RTD with the active region structure of GaN/Al0.2Ga0.8 N/GaN/Al0.2Ga0.8 N (3 nm/1.5 nm/1.5 nm/1.5 nm).

Specific peptide for functionalization of GaN

NASA Astrophysics Data System (ADS)

Estephan, E.; Larroque, C.; Cloitre, T.; Cuisinier, F. J. G.; Gergely, C.

2008-04-01

Nanobiotechnology aims to exploit biomolecular recognition and self-assembly capabilities for integrating advanced materials into medicine and biology. However frequent problems are encountered at the interface of substrate-biological molecule, as the direct physical adsorption of biological molecules is dependent of unpredictable non-specific interactions with the surface, often causing their denaturation. Therefore, a proper functionalization of the substrate should avoid a loss of biological activity. In this work we address the functionalization of the semiconductor GaN (0001) for biosensing applications. The basic interest of using III-V class semiconductors is their good light emitting properties and a fair chemical stability that allows various applications of these materials. The technology chosen to elaborate GaN-specific peptides is the combinatorial phage-display method, a biological screening procedure based on affinity selection. An M13 bacteriophage library has been used to screen 10 10 different peptides against the GaN (0001) surface to finally isolate one specific peptide. The preferential attachment of the biotinylated selected peptide onto the GaN (0001), in close proximity to a surface of different chemical and structural composition has been demonstrated by fluorescence microscopy. Further physicochemical studies have been initiated to evaluate the semiconductor-peptide interface and understand the details in the specific recognition of peptides for semiconductor substrates. Fourier Transform Infrared spectroscopy in Attenuated Total Reflection mode (FTIR-ATR) has been employed to prove the presence of peptides on the surface. Our Atomic Force Microscopy (AFM) studies on the morphology of the GaN surface after functionalization revealed a total surface coverage by a very thin, homogeneous peptide layer. Due to its good biocompatibility, functionalized GaN devices might evolve in a new class of implantable biosensors for medical applications.

ONR Far East Scienticic Bulletin. Volume 11, Number 4, October-December 1986,

DTIC Science & Technology

1986-12-01

magnitude. Visible LEDs are used in large numbers for displays and indicator lights in consumer electronics, and infrared LEDs are used for many kinds of... infrared LDs are used, the Japanese have a large domes- tic market because the use of optical communications systems is widespread. Their devices are of...price between visible lasers used in CDs (=$10 each) and infrared lasers used for communications (=$1000 each). The big market in GaAs solar cells is

Electric microwave absorption for the study of GaAs/AlGaAs heterostructure systems

NASA Astrophysics Data System (ADS)

Zappe, Hans P.; Jantz, Wolfgang

1990-12-01

The use of magnetic-field-dependent microwave absorption as a nondestructive and contact-free means to study transport behavior in GaAs/AlGaAs devices is explored. This technique allows quick measurement of resistance, mobility, and carrier concentration in bulk substrates as well as in the two-dimensional electron gas of heterostructure quantum wells. The two- and three-dimensional conductivities may be separably evaluated, allowing detailed study of conduction in the active layer of high-electron-mobility devices. A brief theoretical foundation is provided, followed by application of the approach to examination of device structural dependencies, carrier-density conduction behavior, and the effects of etch processing on quantum-well integrity.

GaAsPN-based PIN solar cells MBE-grown on GaP substrates: toward the III-V/Si tandem solar cell

NASA Astrophysics Data System (ADS)

Da Silva, M.; Almosni, S.; Cornet, C.; Létoublon, A.; Levallois, C.; Rale, P.; Lombez, L.; Guillemoles, J.-F.; Durand, O.

2015-03-01

GaAsPN semiconductors are promising material for the elaboration of high efficiencies tandem solar cells on silicon substrates. GaAsPN diluted nitride alloy is studied as the top junction material due to its perfect lattice matching with the Si substrate and its ideal bandgap energy allowing a perfect current matching with the Si bottom cell. We review our recent progress in materials development of the GaAsPN alloy and our recent studies of some of the different building blocks toward the elaboration of a PIN solar cell. A lattice matched (with a GaP(001) substrate, as a first step toward the elaboration on a Si substrate) 1μm-thick GaAsPN alloy has been grown by MBE. After a post-growth annealing step, this alloy displays a strong absorption around 1.8-1.9 eV, and efficient photoluminescence at room temperature suitable for the elaboration of the targeted solar cell top junction. Early stage GaAsPN PIN solar cells prototypes have been grown on GaP (001) substrates, with 2 different absorber thicknesses (1μm and 0.3μm). The external quantum efficiencies and the I-V curves show that carriers have been extracted from the GaAsPN alloy absorbers, with an open-circuit voltage of 1.18 V, while displaying low short circuit currents meaning that the GaAsPN structural properties needs a further optimization. A better carrier extraction has been observed with the absorber displaying the smallest thickness, which is coherent with a low carriers diffusion length in our GaAsPN compound. Considering all the pathways for improvement, the efficiency obtained under AM1.5G is however promising.

Rectifying behavior in the GaN/graded-AlxGa1‑xN/GaN double heterojunction structure

NASA Astrophysics Data System (ADS)

Wang, Caiwei; Jiang, Yang; Ma, Ziguang; Zuo, Peng; Yan, Shen; Die, Junhui; Wang, Lu; Jia, Haiqiang; Wang, Wenxin; Chen, Hong

2018-05-01

Rectifying characteristics induced by the polarization fields are achieved in the GaN/graded-AlxGa1‑xN/GaN double heterojunction structure (DHS). By grading AlxGa1‑xN from x  =  0.4(0.3) to 0.1, the DHS displays a better conductivity for smaller reverse bias than for forward bias voltages (reverse rectifying behavior) which is opposite to p–n junction rectifying characteristics. The mechanism of reverse rectifying behavior is illustrated via calculating the energy band structures of the samples. The band gap narrowing caused by decreasing Al composition could compensate the for the band tilt due to the polarization effect in AlxGa1‑xN barriers, thus lowering the barrier height for electron transport from top to bottom. The reverse rectifying behavior could be enhanced by increasing the Al content and the thickness of the multi-layer graded AlxGa1‑xN barriers. This work gives a better understanding of the mechanism of carrier transport in a DHS and makes it possible to realize novel GaN-based heterojunction transistors.

Ga originated kink-and-tail Zn diffusion profiles in InGaAsP and InGaAlAs alloys during MOVPE regrowth

NASA Astrophysics Data System (ADS)

Kitatani, T.; Okamoto, K.; Uchida, K.; Tanaka, S.

2017-12-01

We investigated the diffusion characteristics of Zn in ternary and quaternary alloys of InGaAsP and InGaAlAs, which are important materials in long-wavelength optical communication devices. The measured Zn diffusion profiles of InGaAs, InGaAsP, and InGaAlAs showed kink-and-tail shapes in which Zn concentration fell abruptly at first and then decreased slowly, whereas those of InP and InAlAs showed only abrupt decreases. Thus, only Ga-containing alloys had tail-like profiles. Since this tail was well described by the group-V vacancy related defect model, we deduced that its mechanism is closely related with group-V vacancies in Ga-related bonds such as GaP or GaAs. Furthermore, we demonstrated the possibility that many more group-V vacancies originated from GaP bonds than from GaAs bonds, indicating the difficulty in crystal growth of high quality alloys that have GaP components.

Carrier-induced transient defect mechanism for non-radiative recombination in InGaN light-emitting devices

DOE PAGES

Bang, Junhyeok; Sun, Y. Y.; Song, Jung -Hoon; ...

2016-04-14

Non-radiative recombination (NRR) of excited carriers poses a serious challenge to optoelectronic device efficiency. Understanding the mechanism is thus crucial to defect physics and technological applications. Here, by using first-principles calculations, we propose a new NRR mechanism, where excited carriers recombine via a Frenkel-pair (FP) defect formation. While in the ground state the FP is high in energy and is unlikely to form, in the electronic excited states its formation is enabled by a strong electron-phonon coupling of the excited carriers. As a result, this NRR mechanism is expected to be general for wide-gap semiconductors, rather than being limited tomore » InGaN-based light emitting devices.« less

Review of Defense Display Research Programs

DTIC Science & Technology

2001-01-01

micromirror device (DMD) projection displays, or some future contender, such as organic light emitting diode displays (OLED)—will be installed via...Instruments (TI) digital micromirror device (DMD) technology, developed in an $11.3M research effort managed by the Air Force Research Laboratory from 1991...systems for simulator/trainer systems in the near-mid term and advanced cockpits in the far term. Such large area, curved display systems will require the

Three-dimensional display technologies

PubMed Central

Geng, Jason

2014-01-01

The physical world around us is three-dimensional (3D), yet traditional display devices can show only two-dimensional (2D) flat images that lack depth (i.e., the third dimension) information. This fundamental restriction greatly limits our ability to perceive and to understand the complexity of real-world objects. Nearly 50% of the capability of the human brain is devoted to processing visual information [Human Anatomy & Physiology (Pearson, 2012)]. Flat images and 2D displays do not harness the brain’s power effectively. With rapid advances in the electronics, optics, laser, and photonics fields, true 3D display technologies are making their way into the marketplace. 3D movies, 3D TV, 3D mobile devices, and 3D games have increasingly demanded true 3D display with no eyeglasses (autostereoscopic). Therefore, it would be very beneficial to readers of this journal to have a systematic review of state-of-the-art 3D display technologies. PMID:25530827

77 FR 21994 - Certain Digital Photo Frames and Image Display Devices and Components Thereof; Notice of Request...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-12

... Image Display Devices and Components Thereof; Notice of Request for Written Submissions on Remedy, the... importation, and the sale within the United States after importation of certain digital photo frames and image... the President, has 60 days to approve or disapprove the Commission's action. See section 337(j), 19 U...

On-line data display

NASA Astrophysics Data System (ADS)

Lang, Sherman Y. T.; Brooks, Martin; Gauthier, Marc; Wein, Marceli

1993-05-01

A data display system for embedded realtime systems has been developed for use as an operator's user interface and debugging tool. The motivation for development of the On-Line Data Display (ODD) have come from several sources. In particular the design reflects the needs of researchers developing an experimental mobile robot within our laboratory. A proliferation of specialized user interfaces revealed a need for a flexible communications and graphical data display system. At the same time the system had to be readily extensible for arbitrary graphical display formats which would be required for data visualization needs of the researchers. The system defines a communication protocol transmitting 'datagrams' between tasks executing on the realtime system and virtual devices displaying the data in a meaningful way on a graphical workstation. The communication protocol multiplexes logical channels on a single data stream. The current implementation consists of a server for the Harmony realtime operating system and an application written for the Macintosh computer. Flexibility requirements resulted in a highly modular server design, and a layered modular object- oriented design for the Macintosh part of the system. Users assign data types to specific channels at run time. Then devices are instantiated by the user and connected to channels to receive datagrams. The current suite of device types do not provide enough functionality for most users' specialized needs. Instead the system design allows the creation of new device types with modest programming effort. The protocol, design and use of the system are discussed.

Fabrication, testing and reliability modeling of copper/titanium-metallized GaAs MESFETs and HEMTs for low-noise applications

NASA Astrophysics Data System (ADS)

Feng, Ting

Today, GaAs based field effect transistors (FETs) have been used in a broad range of high-speed electronic military and commercial applications. However, their reliability still needs to be improved. Particularly the hydrogen induced degradation is a large remaining issue in the reliability of GaAs FETs, because hydrogen can easily be incorporated into devices during the crystal growth and virtually every device processing step. The main objective of this research work is to develop a new gate metallization system in order to reduce the hydrogen induced degradation from the gate region for GaAs based MESFETs and HEMTs. Cu/Ti gate metallization has been introduced into the GaAs MESFETs and HEMTs in our work in order to solve the hydrogen problem. The purpose of the use of copper is to tie up the hydrogen atoms and prevent hydrogen penetration into the device active region as well as to keep a low gate resistance for low noise applications. In this work, the fabrication technology of GaAs MESFETs and AlGaAs/GaAs HEMTs with Cu/Ti metallized gates have been successfully developed and the fabricated Cu/Ti FETs have shown comparable DC performance with similar Au-based GaAs FETs. The Cu/Ti FETs were subjected to temperature accelerated testing at NOT under 5% hydrogen forming gas and the experimental results show the hydrogen induced degradation has been reduced for the Cu/Ti FETs compared to commonly used AuPtTi based GaAs FETs. A long-term reliability testing for Cu/Ti FETs has also been carried out at 200°C and up to 1000hours and testing results show Cu/Ti FETs performed with adequate reliability. The failure modes were found to consist of a decrease in drain saturation current and pinch-off voltage and an increase in source ohmic contact resistance. Material characterization tools including Rutherford backscattering spectroscopy and a back etching technique were used in Cu/Ti GaAs FETs, and pronounced gate metal copper in-diffusion and intermixing compounds at the

Significant performance enhancement of InGaN/GaN nanorod LEDs with multi-layer graphene transparent electrodes by alumina surface passivation.

PubMed

Latzel, M; Büttner, P; Sarau, G; Höflich, K; Heilmann, M; Chen, W; Wen, X; Conibeer, G; Christiansen, S H

2017-02-03

Nanotextured surfaces provide an ideal platform for efficiently capturing and emitting light. However, the increased surface area in combination with surface defects induced by nanostructuring e.g. using reactive ion etching (RIE) negatively affects the device's active region and, thus, drastically decreases device performance. In this work, the influence of structural defects and surface states on the optical and electrical performance of InGaN/GaN nanorod (NR) light emitting diodes (LEDs) fabricated by top-down RIE of c-plane GaN with InGaN quantum wells was investigated. After proper surface treatment a significantly improved device performance could be shown. Therefore, wet chemical removal of damaged material in KOH solution followed by atomic layer deposition of only 10 [Formula: see text] alumina as wide bandgap oxide for passivation were successfully applied. Raman spectroscopy revealed that the initially compressively strained InGaN/GaN LED layer stack turned into a virtually completely relaxed GaN and partially relaxed InGaN combination after RIE etching of NRs. Time-correlated single photon counting provides evidence that both treatments-chemical etching and alumina deposition-reduce the number of pathways for non-radiative recombination. Steady-state photoluminescence revealed that the luminescent performance of the NR LEDs is increased by about 50% after KOH and 80% after additional alumina passivation. Finally, complete NR LED devices with a suspended graphene contact were fabricated, for which the effectiveness of the alumina passivation was successfully demonstrated by electroluminescence measurements.

Micro-processing of NiMnGa shape memory alloy by using a nanosecond fiber laser

NASA Astrophysics Data System (ADS)

Biffi, C. A.; Tuissi, A.

2016-04-01

The interest on Ferromagnetic Shape Memory Alloys (FSMAs), such as NiMnGa, is growing up, thanks to their functional properties to be employed in a new class of micro-devices. The most evident critical issue, limiting the use of these systems in the production of industrial devices, is the brittleness of the bulk material; its workability by using convectional processing methods is very limited. Thus, alternative processing methods, including laser processing, are encouraged for the manufacture of FSMAs based new devices. In this work, the effect of the nanosecond laser microprocessing on Ni45Mn33Ga22 [at%] has been studied. Linear grooves were realized by a nanosecond 30 W fiber laser; the machined surfaces were analyzed with scanning electron microscopy, coupled with energetic dispersion spectroscopy for the composition analysis. The morphology of the grooves was affected by the laser scanning velocity and the number of laser pulses while the measured material removal rate appeared to be influenced mainly by the number of laser pulses. Compositional modification, associated to the loss of Ga content, was detected only for the lower scanning velocity, because of the high fluence. On the contrary, by increasing the velocity up to 1000 mm/s no Ga loss can be seen, making possible the laser processing of this functional alloy without its chemical modification. The use of short pulses allowed also to reduce the amount of recast material and the compositional change with respect to long pulses. Finally, the calorimetric analysis indicated that laser nanosecond microprocessing could affect the functional properties of this alloy: a larger decrease of the characteristic temperatures of the martensitic transformation was observed in correspondence of the low scanning velocity.

Quantum well infrared photodetectors (QWIP) with selectively regrown N-GaAs plugs

NASA Astrophysics Data System (ADS)

Matsukura, Yusuke; Nishino, Hironori; Tanaka, Hitoshi; Fujii, Toshio

2001-10-01

We fabricated the GaAs/AlGaAs Quantum Well Infrared Photo detector (QWIP) focal plane array with selectively re-grown N- GaAs interconnection plugs and demonstrated its device operation, in order to establish the technology to obtain both complex device functions and device manufacturability. MBE (Molecular Beam Epitaxy) grown QWIP MQW wafers were covered with SiON and SiNx mask films to obtain selectivity of the re-growth process. N-GaAs plugs were re-grown selectively with low-pressure MOCVD (Metal-Organic Chemical Vapor Deposition) with AsH3 and Dimethylgalliumchloride as precursors, only on the bottom surfaces of the holes for the interconnection to extract the electrodes from the underlying epilayer. Cross- sectional SEM observation revealed that the feature of the re- grown N-GaAs plugs was triangular, rather than rectangular as expected. The reason for this discrepancy is not yet clear. The electrical contact between the epilayer and re-grown N- GaAs plug was 'ohmic-like,' without any trace of interfacial barrier. The Current-Voltage characteristics of the fabricated QWIP device showed no tangible leakage current between the N- GaAs plug and device structure, indicating that electrical insulation between the N-GaAs plugs and device structure was sufficient. Fabricated devices were successfully operated as a hybrid focal plane array, indicating the selective re-growth was a promising technique to realize complex QWIP based devices.

Room temperature electroluminescence from n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction device grown by PLD

NASA Astrophysics Data System (ADS)

Zhang, Lichun; Li, Qingshan; Wang, Feifei; Qu, Chong; Zhao, Fengzhou

2014-05-01

The n-ZnO:Ga/ p-GaN:Mg and n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated by the pulsed laser deposition (PLD) technique. The blue electroluminescence (EL) of the n-ZnO:Ga/ p-GaN:Mg heterojunction LEDs is emitted mainly from the p-GaN layer instead of the n-ZnO:Ga layer, for the reason that the electron injection from n-ZnO:Ga prevailed over the hole injection from p-GaN:Mg due to the higher carrier concentration and carrier mobility in n-ZnO:Ga. On the other hand, the n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction LEDs exhibited dominant ultraviolet-blue emission. The reason for this difference is attributed to the inserted undoped i-ZnO layer between n-ZnO:Ga and p-GaN:Mg, in which the holes from p-GaN:Mg and the electrons from n-ZnO:Ga are recombined.

A Study of Photoluminiscence and UV-Vis in Enhanced GaN Nanofibers

NASA Astrophysics Data System (ADS)

Robles-Garcia, Joshua; Melendez-Zambrana, Anamaris; Ramos, Idalia

2014-03-01

The photoluminiscence (PL) and UV-Vis properties of Gallium Nitride (GaN) nanofibers were investigated for samples fabricated with a precursor solution containing Gallium Nitrate Hydrate, Cellulose Acetate, and Urea in the solvents Dimethylacetamide (DMA) and Acetone. GaN is a wide bandgap (3.4 eV) semiconductor that can be used in a variety of applications including solid-state lighting, high power, and high frequency devices. In previous work, we produced polycrystalline GaN nanofibers with wurtzite structure, using the electrospinning method and a thermal treatment in nitrogen and ammonia at 1000C. In this research we study the addition of urea to the precursor solution to enhance the crystallinity of the fibers at lower sintering temperatures. The molar ratios of urea added to the precursor range from 0 to 1.7 M. After electrospinning the fibers were sintered in Nitrogen at 450C for 3 hours and then, under ammonia gas flow at 900C for 5 hours. X-Ray Diffraction (XRD), UV-Vis spectroscopy, and PL measurements at room temperature were used to study the structural and optical properties of the fibers during the sintering process. This work was sponsored by UPRH PREM (NSF-DMR-0934195).

Determination of the strain distribution for the Si3N4 passivated AlGaN/AlN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Fu, Chen; Lin, Zhaojun; Liu, Yan; Cui, Peng; Lv, Yuanjie; Zhou, Yang; Dai, Gang; Luan, Chongbiao

2017-11-01

A method to determine the strain distribution of the AlGaN barrier layer after the device fabrication and the passivation process has been presented. By fitting the calculated parasitic source access resistance with the measured ones for the AlGaN/AlN/GaN HFETs and using the polarization Coulomb field scattering theory, the strain variation of the AlGaN barrier layer after the passivation process has been quantitatively studied. The results show that the tensile strain in the access regions of the AlGaN barrier layer has been increased by 4.62% for the 250 nm-Si3N4 passivated device, and has been decreased by 2.0% for the 400 nm-Si3N4 passivated device, compared to that of before the passivation, respectively. For the gate region of the two devices, the tensile strain has been decreased by 60.77% and increased by 3.60% after the passivation of different thicknesses, oppositely.

Hydrothermal Synthesis and Photocatalytic Property of β-Ga2O3 Nanorods

NASA Astrophysics Data System (ADS)

Reddy, L. Sivananda; Ko, Yeong Hwan; Yu, Jae Su

2015-09-01

Gallium oxide (Ga2O3) nanorods were facilely prepared by a simple hydrothermal synthesis, and their morphology and photocatalytic property were studied. The gallium oxide hydroxide (GaOOH) nanorods were formed in aqueous growth solution containing gallium nitrate and ammonium hydroxide at 95 °C of growth temperature. Through the calcination treatment at 500 and 1000 °C for 3 h, the GaOOH nanorods were converted into single crystalline α-Ga2O3 and β-Ga2O3 phases. From X-ray diffraction analysis, it could be confirmed that a high crystalline quality of β-Ga2O3 nanorods was achieved by calcinating at 1000 °C. The thermal behavior of the Ga2O3 nanorods was also investigated by differential thermal analysis, and their vibrational bands were identified by Fourier transform infrared spectroscopy. In order to examine the photocatalytic activity of samples, the photodegradation of Rhodamine B solution was observed under UV light irradiation. As a result, the α-Ga2O3 and β-Ga2O3 nanorods exhibited high photodegeneration efficiencies of 62 and 79 %, respectively, for 180 min of UV irradiation time.

Hydrothermal Synthesis and Photocatalytic Property of β-Ga2O3 Nanorods.

PubMed

Reddy, L Sivananda; Ko, Yeong Hwan; Yu, Jae Su

2015-12-01

Gallium oxide (Ga2O3) nanorods were facilely prepared by a simple hydrothermal synthesis, and their morphology and photocatalytic property were studied. The gallium oxide hydroxide (GaOOH) nanorods were formed in aqueous growth solution containing gallium nitrate and ammonium hydroxide at 95 °C of growth temperature. Through the calcination treatment at 500 and 1000 °C for 3 h, the GaOOH nanorods were converted into single crystalline α-Ga2O3 and β-Ga2O3 phases. From X-ray diffraction analysis, it could be confirmed that a high crystalline quality of β-Ga2O3 nanorods was achieved by calcinating at 1000 °C. The thermal behavior of the Ga2O3 nanorods was also investigated by differential thermal analysis, and their vibrational bands were identified by Fourier transform infrared spectroscopy. In order to examine the photocatalytic activity of samples, the photodegradation of Rhodamine B solution was observed under UV light irradiation. As a result, the α-Ga2O3 and β-Ga2O3 nanorods exhibited high photodegeneration efficiencies of 62 and 79 %, respectively, for 180 min of UV irradiation time.

15.3%-Efficient GaAsP Solar Cells on GaP/Si Templates

DOE PAGES

Vaisman, Michelle; Fan, Shizhao; Nay Yaung, Kevin; ...

2017-07-26

As single-junction Si solar cells approach their practical efficiency limits, a new pathway is necessary to increase efficiency in order to realize more cost-effective photovoltaics. Integrating III-V cells onto Si in a multijunction architecture is a promising approach that can achieve high efficiency while leveraging the infrastructure already in place for Si and III-V technology. In this Letter, we demonstrate a record 15.3%-efficient 1.7 eV GaAsP top cell on GaP/Si, enabled by recent advances in material quality in conjunction with an improved device design and a high-performance antireflection coating. Furthermore, we present a separate Si bottom cell with a 1.7more » eV GaAsP optical filter to absorb most of the visible light with an efficiency of 6.3%, showing the feasibility of monolithic III-V/Si tandems with >20% efficiency. Through spectral efficiency analysis, we also compare our results to previously published GaAsP and Si devices, projecting tandem GaAsP/Si efficiencies of up to 25.6% based on current state-of-the-art individual subcells. With the aid of modeling, we further illustrate a realistic path toward 30% GaAsP/Si tandems for high-efficiency, monolithically integrated photovoltaics.« less

Characterization of InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

NASA Technical Reports Server (NTRS)

Ketterson, Andrew A.; Masselink, William T.; Gedymin, Jon S.; Klem, John; Peng, Chin-Kun

1986-01-01

High-performance pseudomorphic In(y)Ga(1-y)As/Al0.15-Ga0.85As y = 0.05-0.2 MODFET's grown by MBE have been characterized at dc (300 and 77 K) and RF frequencies. Transconductances as high 310 and 380 mS/mm and drain currents as high as 290 and 310 mA/mm were obtained at 300 and 77 K, respectively, for 1-micron gate lengths and 3-micron source-drain spacing devices. Lack of persistent trapping effects, I-V collapse, and threshold voltage shifts observed with these devices are attributed to the use of low mole fraction Al(x)Ga(1-x)As while still maintaining two-dimensional electron gas concentrations of about 1.3 x to the 12th per sq cm. Detailed microwave S-parameter measurements indicate a current gain cut-off frequency of 24.5 GHz when y = 0.20, which is as much as 100 percent better than similar GaAs/AlGaAs MODFET structures, and a maximum frequency of oscillation of 40 GHz.

Performance enhancement of GaN ultraviolet avalanche photodiodes with p-type δ-doping

NASA Astrophysics Data System (ADS)

Bayram, C.; Pau, J. L.; McClintock, R.; Razeghi, M.

2008-06-01

High quality δ-doped p-GaN is used as a means of improving the performance of back-illuminated GaN avalanche photodiodes (APDs). Devices with δ-doped p-GaN show consistently lower leakage current and lower breakdown voltage than those with bulk p-GaN. APDs with δ-doped p-GaN also achieve a maximum multiplication gain of 5.1×104, more than 50 times higher than that obtained in devices with bulk p-GaN. The better device performance of APDs with δ-doped p-GaN is attributed to the higher structural quality of the p-GaN layer achieved via δ-doping.

Transport Equations for CAD Modeling of Al(x)Ga(1-x)N/GaN HEMTs

NASA Technical Reports Server (NTRS)

Freeman, Jon C.

2003-01-01

BEMTs formed from Al(x)Ga(1-x)N/GaN heterostructures are being investigated for high RF power and efficiency around the world by many groups, both academic and industrial. In these devices, the 2DEG formation is dominated by both spontaneous and piezoelectric polarization fields, with each component having nearly the same order of magnitude. The piezoelectric portion is induced by the mechanical strain in the structure, and to analyze these devices, one must incorporate the stress/strain relationships, along with the standard semiconductor transport equations. These equations for Wurtzite GaN are not easily found in the open literature, hence this paper summarizes them, along with the constitutive equations for piezoelectric materials. The equations are cast into the format for the Wurtzite crystal class, which is the most common way GaN is grown epitaxially.

Optical gain in GaAsBi/GaAs quantum well diode lasers

PubMed Central

Marko, Igor P.; Broderick, Christopher A.; Jin, Shirong; Ludewig, Peter; Stolz, Wolfgang; Volz, Kerstin; Rorison, Judy M.; O’Reilly, Eoin P.; Sweeney, Stephen J.

2016-01-01

Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10–15 cm−1 and a peak modal gain of 24 cm−1, corresponding to a material gain of approximately 1500 cm−1 at a current density of 2 kA cm−2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared. PMID:27363930

Normally-off p-GaN/AlGaN/GaN high electron mobility transistors using hydrogen plasma treatment

NASA Astrophysics Data System (ADS)

Hao, Ronghui; Fu, Kai; Yu, Guohao; Li, Weiyi; Yuan, Jie; Song, Liang; Zhang, Zhili; Sun, Shichuang; Li, Xiajun; Cai, Yong; Zhang, Xinping; Zhang, Baoshun

2016-10-01

In this letter, we report a method by introducing hydrogen plasma treatment to realize normally-off p-GaN/AlGaN/GaN HEMT devices. Instead of using etching technology, hydrogen plasma was adopted to compensate holes in the p-GaN above the two dimensional electron gas (2DEG) channel to release electrons in the 2DEG channel and form high-resistivity area to reduce leakage current and increase gate control capability. The fabricated p-GaN/AlGaN/GaN HEMT exhibits normally-off operation with a threshold voltage of 1.75 V, a subthreshold swing of 90 mV/dec, a maximum transconductance of 73.1 mS/mm, an ON/OFF ratio of 1 × 107, a breakdown voltage of 393 V, and a maximum drain current density of 188 mA/mm at a gate bias of 6 V. The comparison of the two processes of hydrogen plasma treatment and p-GaN etching has also been made in this work.

Effect of p-GaN layer doping on the photoresponse of GaN-based p-i-n ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Wang, Jun; Guo, Jin; Xie, Feng; Wang, Wanjun; Wang, Guosheng; Wu, Haoran; Wang, Tanglin; Song, Man

2015-08-01

We report on two-dimensional (2D) numerical simulations of photoresponse characteristics for GaN based p-i-n ultraviolet (UV) photodetectors. Effects of doping density of p-GaN layer on the photoresponse have been investigated. In order to accurately simulate the device performance, the theoretical calculation includes doping-dependent mobility degradation by Arora model and high field saturation model. Theoretical modeling shows that the doping density of p- GaN layer can significantly affect the photoresponse of GaN based p-i-n UV photodetectors, especially at schottky contact. We have to make a suitable choice of the doping in the device design according to the simulation results.

Magnetometory Measurement of AlGaN/GaN 2DEG

NASA Astrophysics Data System (ADS)

Tsubaki, K.; Maeda, N.; Saitoh, T.; Kobayashi, N.

2004-03-01

AlGaN/GaN heterostructure devices have been attracting much attention because of their potential for high-performance microwave applications. Therefore, the electronic properties of a 2DEG in AlGaN/GaN heterostructures have recently been discussed. In this paper, we performed the magnetometory measurement of AlGaN/GaN 2DEG at low temperature. The AlGaN/GaN heterostructures were grown by low-pressure metal-organic chemical vapour phase epitaxy on (0001) SiC substrate using AlN buffers. The electron mobility and electron concentration at 4.2 K are 9,540 cm^2/Vs and 6.6 × 10^12 cm-2, respectively. When the temperature is lower than 4.5 K the hysteresis of magnetometric data is observed near zero magnetic field. At the temperature larger than 4.5 K, the hysteresis of magnetometric data disappears and the slope of magnetometric data with respect to magnetic field becomes lower as obeying Currie-Weiss law. In general the hysteresis and Currie-Weiss law behavior in magnetometric data imply the possibility of the ferromagnetism, but the conformation of the ferromagnetism of AlGaN/GaN heterostructure is still difficult and the detailed physical mechanism is still unclear.

Design and fabrication of GaAs OMIST photodetector

NASA Astrophysics Data System (ADS)

Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

1998-08-01

We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

Development of orientation-patterned GaP grown on foreign substrates for QPM frequency conversion devices

NASA Astrophysics Data System (ADS)

Vangala, Shivashankar; Peterson, Rita; Snure, Michael; Tassev, Vladimir

2017-02-01

Thick hydride vapor phase epitaxially grown orientation-patterned gallium phosphide (OPGaP) is a leading material for quasi-phase matching (QPM) frequency conversion in the mid- and longwave infrared (IR). This is due to its negligible two-photon absorption (2PA) in the convenient pumping range 1 - 1.7 μm, compared with the 2PA of some traditional QPM materials, such as GaAs. In this paper, we describe homo- and heteroepitaxial growth techniques aimed to produce hundreds of microns thick OPGaP on: 1) OPGaAs templates fabricated using an improved wafer-fusion process; 2) OPGaAs templates fabricated by using a molecular beam epitaxy (MBE) for sublattice polarity inversion, but one with and one without MBE regrowth after the inversion. Some of the advantages of the heteroepitaxial growth of OPGaP on OPGaAs templates include: 1) achieving good domain fidelity as a result of the significantly higher OPGaAs template quality; 2) eliminating the needs of using the poor quality commercially available GaP in the production of thick OPGaP material, and 3) suppression of the additional absorption band between 2 - 4 μm (which is due to incorporation of n-type impurities) and, in general, improvement of the IR transmittance in the entire IR region. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, will accelerate the development of high power, broadly tunable laser sources in the IR which, in addition, will be offered with higher device quality and at a reasonably lower unit cost.

Simultaneous dual-functioning InGaN/GaN multiple-quantum-well diode for transferrable optoelectronics

NASA Astrophysics Data System (ADS)

Shi, Zheng; Yuan, Jialei; Zhang, Shuai; Liu, Yuhuai; Wang, Yongjin

2017-10-01

We propose a wafer-level procedure for the fabrication of 1.5-mm-diameter dual functioning InGaN/GaN multiple-quantum-well (MQW) diodes on a GaN-on-silicon platform for transferrable optoelectronics. Nitride semiconductor materials are grown on (111) silicon substrates with intermediate Al-composition step-graded buffer layers, and membrane-type MQW-diode architectures are obtained by a combination of silicon removal and III-nitride film backside thinning. Suspended MQW-diodes are directly transferred from silicon to foreign substrates such as metal, glass and polyethylene terephthalate by mechanically breaking the support beams. The transferred MQW-diodes display strong electroluminescence under current injection and photodetection under light irradiation. Interestingly, they demonstrate a simultaneous light-emitting light-detecting function, endowing the 1.5-mm-diameter MQW-diode with the capability of producing transferrable optoelectronics for adjustable displays, wearable optical sensors, multifunctional energy harvesting, flexible light communication and monolithic photonic circuit.

Conversion between hexagonal GaN and beta-Ga(2)O(3) nanowires and their electrical transport properties.

PubMed

Li, Jianye; An, Lei; Lu, Chenguang; Liu, Jie

2006-02-01

We have observed that the hexagonal GaN nanowires grown from a simple chemical vapor deposition method using gallium metal and ammonia gas are usually gallium-doped. By annealing in air, the gallium-doped hexagonal GaN nanowires could be completely converted to beta-Ga(2)O(3) nanowires. Annealing the beta-Ga(2)O(3) nanowires in ammonia could convert them back to undoped hexagonal GaN nanowires. Field effect transistors based on these three kinds of nanowires were fabricated, and their performances were studied. Because of gallium doping, the as-grown GaN nanowires show a weak gating effect. Through the conversion process of GaN nanowires (gallium-doped) --> Ga(2)O(3) nanowires --> GaN nanowires (undoped) via annealing, the final undoped GaN nanowires display different electrical properties than the initial gallium-doped GaN nanowires, show a pronounced n-type gating effect, and can be completely turned off.

Vacuum status-display and sector-conditioning programs

NASA Astrophysics Data System (ADS)

Skelly, J.; Yen, S.

1990-08-01

Two programs have been developed for observation and control of the AGS vacuum system, which include the following notable features: (1) they incorporate a graphical user interface and (2) they are driven by a relational database which describes the vacuum system. The vacuum system comprises some 440 devices organized into 28 vacuum sectors. The status-display program invites menu selection of a sector, interrogates the relational database for relevant vacuum devices, acquires live readbacks and posts a graphical display of their status. The sector-conditioning program likewise invites sector selection, produces the same status display and also implements process control logic on the sector devices to pump the sector down from atmospheric pressure to high vacuum over a period extending several hours. As additional devices are installed in the vacuum system, the devices are added to the relational database; these programs then automatically include the new devices.

Structural dependences of localization and recombination of photogenerated carriers in the top GaInP Subcells of GaInP/GaAs double-junction tandem solar cells.

PubMed

Deng, Zhuo; Ning, Jiqiang; Su, Zhicheng; Xu, Shijie; Xing, Zheng; Wang, Rongxin; Lu, Shulong; Dong, Jianrong; Zhang, Baoshun; Yang, Hui

2015-01-14

In high-efficiency GaInP/GaAs double-junction tandem solar cells, GaInP layers play a central role in determining the performance of the solar cells. Therefore, gaining a deeper understanding of the optoelectronic processes in GaInP layers is crucial for improving the energy conversion efficiency of GaInP-based photovoltaic devices. In this work, we firmly show strong dependences of localization and recombination of photogenerated carriers in the top GaInP subcells in the GaInP/GaAs double-junction tandem solar cells on the substrate misorientation angle with excitation intensity- and temperature-dependent photoluminescence (PL). The entire solar cell structures including GaInP layers were grown with metalorganic chemical vapor deposition on GaAs substrates with misorientation angles of 2° (denoted as Sample 2°) and 7° (Sample 7°) off (100) toward (111)B. The PL spectral features of the two top GaInP subcells, as well as their excitation-power and temperature dependences exhibit remarkable variation on the misorientation angle. In Sample 2°, the dominant localization mechanism and luminescence channels are due to the energy potential minima caused by highly ordered atomic domains; In Sample 7°, the main localization and radiative recombination of photogenerated carriers occur in the atomically disordered regions. Our results reveal a more precise picture on the localization and recombination mechanisms of photogenerated carriers in the top GaInP subcells, which could be the crucial factors in controlling the optoelectronic efficiency of the GaInP-based multijunction photovoltaic devices.

Distributed bragg reflector using AIGaN/GaN

DOEpatents

Waldrip, Karen E.; Lee, Stephen R.; Han, Jung

2004-08-10

A supported distributed Bragg reflector or superlattice structure formed from a substrate, a nucleation layer deposited on the substrate, and an interlayer deposited on the nucleation layer, followed by deposition of (Al,Ga,B)N layers or multiple pairs of (Al,Ga,B)N/(Al,Ga,B)N layers, where the interlayer is a material selected from AlN, Al.sub.x Ga.sub.1-x N, and AlBN with a thickness of approximately 20 to 1000 angstroms. The interlayer functions to reduce or eliminate the initial tensile growth stress, thereby reducing cracking in the structure. Multiple interlayers utilized in an AlGaN/GaN DBR structure can eliminate cracking and produce a structure with a reflectivity value greater than 0.99.

Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices

NASA Astrophysics Data System (ADS)

Sharma, Chandan; Laishram, Robert; Amit, Rawal, Dipendra Singh; Vinayak, Seema; Singh, Rajendra

2017-08-01

This article reports an experimental approach to analyze the kink effect phenomenon which is usually observed during the GaN high electron mobility transistor (HEMT) operation. De-trapping of charge carriers is one of the prominent reasons behind the kink effect. The commonly observed non-monotonic behavior of kink pattern is analyzed under two different device operating conditions and it is found that two different de-trapping mechanisms are responsible for a particular kink behavior. These different de-trapping mechanisms are investigated through a time delay analysis which shows the presence of traps with different time constants. Further voltage sweep and temperature analysis corroborates the finding that different de-trapping mechanisms play a role in kink behavior under different device operating conditions.

Simulation of thermal management in AlGaN/GaN HEMTs with integrated diamond heat spreaders

NASA Astrophysics Data System (ADS)

Wang, A.; Tadjer, M. J.; Calle, F.

2013-05-01

We investigated the impact of diamond heat spreading layers on the performance of AlGaN/GaN high-electron-mobility-transistors (HEMTs). A finite element method was used to simulate the thermal and electrical characteristics of the devices under dc and pulsed operation conditions. The results show that the device performance can be improved significantly by optimized heat spreading, an effect strongly dependent on the lateral thermal conductivity of the initial several micrometers of diamond deposition. Of crucial importance is the proximity of the diamond layer to the heat source, which makes this method advantageous over other thermal management procedures, especially for the device in pulsed operation. In this case, the self-heating effect can be suppressed, and it is not affected by either the substrate or its thermal boundary resistance at the GaN/substrate at wider pulses. The device with a 5 µm diamond layer can present 10.5% improvement of drain current, and the self-heating effect can be neglected for a 100 ns pulse width at 1 V gate and 20 V drain voltage.

GaAs MOEMS Technology

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

SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.

2003-03-01

Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vitalmore » step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.« less

Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser

NASA Astrophysics Data System (ADS)

Ludewig, P.; Knaub, N.; Hossain, N.; Reinhard, S.; Nattermann, L.; Marko, I. P.; Jin, S. R.; Hild, K.; Chatterjee, S.; Stolz, W.; Sweeney, S. J.; Volz, K.

2013-06-01

The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of ˜947 nm. These results from broad area devices show great promise for developing efficient IR laser diodes based on this emerging materials system.

Double-layered liquid crystal light shutter for control of absorption and scattering of the light incident to a transparent display device

NASA Astrophysics Data System (ADS)

Huh, Jae-Won; Yu, Byeong-Hun; Shin, Dong-Myung; Yoon, Tae-Hoon

2015-03-01

Recently, a transparent display has got much attention as one of the next generation display devices. Especially, active studies on a transparent display using organic light-emitting diodes (OLEDs) are in progress. However, since it is not possible to obtain black color using a transparent OLED, it suffers from poor visibility. This inevitable problem can be solved by using a light shutter. Light shutter technology can be divided into two types; light absorption and scattering. However, a light shutter based on light absorption cannot block the background image perfectly and a light shutter based on light scattering cannot provide black color. In this work we demonstrate a light shutter using two liquid crystal (LC) layers, a light absorption layer and a light scattering layer. To realize a light absorption layer and a light scattering layer, we use the planar state of a dye-doped chiral nematic LC (CNLC) cell and the focal-conic state of a long-pitch CNLC cell, respectively. The proposed light shutter device can block the background image perfectly and show black color. We expect that the proposed light shutter can increase the visibility of a transparent display.

Single nanowire green InGaN/GaN light emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Guogang; Li, Ziyuan; Yuan, Xiaoming; Wang, Fan; Fu, Lan; Zhuang, Zhe; Ren, Fang-Fang; Liu, Bin; Zhang, Rong; Tan, Hark Hoe; Jagadish, Chennupati

2016-10-01

Single nanowire (NW) green InGaN/GaN light-emitting diodes (LEDs) were fabricated by top-down etching technology. The electroluminescence (EL) peak wavelength remains approximately constant with an increasing injection current in contrast to a standard planar LED, which suggests that the quantum-confined Stark effect is significantly reduced in the single NW device. The strain relaxation mechanism is studied in the single NW LED using Raman scattering analysis. As compared to its planar counterpart, the EL peak of the NW LED shows a redshift, due to electric field redistribution as a result of changes in the cavity mode pattern after metallization. Our method has important implication for single NW optoelectronic device applications.

High power ultraviolet light emitting diodes based on GaN /AlGaN quantum wells produced by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Cabalu, J. S.; Bhattacharyya, A.; Thomidis, C.; Friel, I.; Moustakas, T. D.; Collins, C. J.; Komninou, Ph.

2006-11-01

In this paper, we report on the growth by molecular beam epitaxy and fabrication of high power nitride-based ultraviolet light emitting diodes emitting in the spectral range between 340 and 350nm. The devices were grown on (0001) sapphire substrates via plasma-assisted molecular beam epitaxy. The growth of the light emitting diode (LED) structures was preceded by detailed materials studies of the bottom n-AlGaN contact layer, as well as the GaN /AlGaN multiple quantum well (MQW) active region. Specifically, kinetic conditions were identified for the growth of the thick n-AlGaN films to be both smooth and to have fewer defects at the surface. Transmission-electron microscopy studies on identical GaN /AlGaN MQWs showed good quality and well-defined interfaces between wells and barriers. Large area mesa devices (800×800μm2) were fabricated and were designed for backside light extraction. The LEDs were flip-chip bonded onto a Si submount for better heat sinking. For devices emitting at 340nm, the measured differential on-series resistance is 3Ω with electroluminescence spectrum full width at half maximum of 18nm. The output power under dc bias saturates at 0.5mW, while under pulsed operation it saturates at approximately 700mA to a value of 3mW, suggesting that thermal heating limits the efficiency of these devices. The output power of the investigated devices was found to be equivalent with those produced by the metal-organic chemical vapor deposition and hydride vapor-phase epitaxy methods. The devices emitting at 350nm were investigated under dc operation and the output power saturates at 4.5mW under 200mA drive current.

75 FR 445 - In the Matter of Certain Liquid Crystal Display Devices and Products Containing the Same; Notice...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-01-05

... Display Devices and Products Containing the Same; Notice of Investigation AGENCY: U.S. International Trade Commission. ACTION: Institution of investigation pursuant to 19 U.S.C. 1337. SUMMARY: Notice is hereby given that a complaint was filed with the U.S. International Trade Commission on December 1, 2009, under...

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices

PubMed Central

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-01-01

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers. PMID:27181337

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices.

PubMed

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-05-16

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers.

Design of high breakdown voltage GaN vertical HFETs with p-GaN buried buffer layers for power switching applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Liu, Dong; Zhao, Ziqi; Bai, Zhiyuan; Li, Liang; Mo, Jianghui; Yu, Qi

2015-07-01

To achieve a high breakdown voltage, a GaN vertical heterostructure field effect transistor with p-GaN buried layers (PBL-VHFET) is proposed in this paper. The breakdown voltage of this GaN-based PBL-VHFET could be improved significantly by the optimizing thickness of p-GaN buried layers and doping concentration in PBL. When the GaN buffer layer thickness is 15 μm, the thickness, length and p-doping concentration of PBL are 0.3 μm, 2.7 μm, and 3 × 1017 cm-3, respectively. Simulation results show that the breakdown voltage and on-resistance of the device with two p-GaN buried layers are 3022 V and 3.13 mΩ cm2, respectively. The average breakdown electric field would reach as high as 201.5 V/μm. Compared with the typical GaN vertical heterostructure FETs without PBL, both of breakdown voltage and average breakdown electric field of device are increased more than 50%.

Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

PubMed

Hsieh, Chin-Hua; Chang, Mu-Tung; Chien, Yu-Jen; Chou, Li-Jen; Chen, Lih-Juann; Chen, Chii-Dong

2008-10-01

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

Mid-infrared Photoconductive Response in AlGaN/GaN Step Quantum Wells

PubMed Central

Rong, X.; Wang, X. Q.; Chen, G.; Zheng, X. T.; Wang, P.; Xu, F. J.; Qin, Z. X.; Tang, N.; Chen, Y. H.; Sang, L. W.; Sumiya, M.; Ge, W. K.; Shen, B.

2015-01-01

AlGaN/GaN quantum structure is an excellent candidate for high speed infrared detectors based on intersubband transitions. However, fabrication of AlGaN/GaN quantum well infrared detectors suffers from polarization-induced internal electric field, which greatly limits the carrier vertical transport. In this article, a step quantum well is proposed to attempt solving this problem, in which a novel spacer barrier layer is used to balance the internal electric field. As a result, a nearly flat band potential profile is obtained in the step barrier layers of the AlGaN/GaN step quantum wells and a bound-to-quasi-continuum (B-to-QC) type intersubband prototype device with detectable photocurrent at atmosphere window (3–5 μm) is achieved in such nitride semiconductors. PMID:26395756

Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

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

Swain, Basudev, E-mail: Swain@iae.re.kr; Mishra, Chinmayee; Lee, Chan Gi

2015-07-15

Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga{sub 0.97}N{sub 0.9}O{sub 0.09} is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga{sub 0.97}N{sub 0.9}O{sub 0.09} of the MOCVD dust is leached at the optimum condition. Subsequently, the leachmore » residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4 M HCl, 100 °C and pulp density of 100 kg/m{sup 3,} respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. - Highlights: • Waste MOCVD dust is treated through mechanochemical leaching. • GaN is hardly leached, and converted to NaGaO{sub 2} through ball milling and annealing. • Process for gallium recovery from waste MOCVD dust has been developed. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} is revealed. • Solid-state chemistry involved in this process is reported.« less

Enhanced Solar Cell Conversion Efficiency of InGaN/GaN Multiple Quantum Wells by Piezo-Phototronic Effect.

PubMed

Jiang, Chunyan; Jing, Liang; Huang, Xin; Liu, Mengmeng; Du, Chunhua; Liu, Ting; Pu, Xiong; Hu, Weiguo; Wang, Zhong Lin

2017-09-26

The piezo-phototronic effect is the tuning of piezoelectric polarization charges at the interface to largely enhance the efficiency of optoelectronic processes related to carrier separation or recombination. Here, we demonstrated the enhanced short-circuit current density and the conversion efficiency of InGaN/GaN multiple quantum well solar cells with an external stress applied on the device. The external-stress-induced piezoelectric charges generated at the interfaces of InGaN and GaN compensate the piezoelectric charges induced by lattice mismatch stress in the InGaN wells. The energy band realignment is calculated with a self-consistent numerical model to clarify the enhancement mechanism of optical-generated carriers. This research not only theoretically and experimentally proves the piezo-phototronic effect modulated the quantum photovoltaic device but also provides a great promise to maximize the use of solar energy in the current energy revolution.

High-frequency output characteristics of AlGaAs/GaAs heterojunction bipolar transistors for large-signal applications

NASA Astrophysics Data System (ADS)

Chen, J.; Gao, G. B.; Ünlü, M. S.; Morkoç, H.

1991-11-01

High-frequency ic- vce output characteristics of bipolar transistors, derived from calculated device cutoff frequencies, are reported. The generation of high-frequency output characteristics from device design specifications represents a novel bridge between microwave circuit design and device design: the microwave performance of simulated device structures can be analyzed, or tailored transistor device structures can be designed to fit specific circuit applications. The details of our compact transistor model are presented, highlighting the high-current base-widening (Kirk) effect. The derivation of the output characteristics from the modeled cutoff frequencies are then presented, and the computed characteristics of an AlGaAs/GaAs heterojunction bipolar transistor operating at 10 GHz are analyzed. Applying the derived output characteristics to microwave circuit design, we examine large-signal class A and class B amplification.

GaN based nanorods for solid state lighting

NASA Astrophysics Data System (ADS)

Li, Shunfeng; Waag, Andreas

2012-04-01

In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

Present status of amorphous In-Ga-Zn-O thin-film transistors.

PubMed

Kamiya, Toshio; Nomura, Kenji; Hosono, Hideo

2010-08-01

The present status and recent research results on amorphous oxide semiconductors (AOSs) and their thin-film transistors (TFTs) are reviewed. AOSs represented by amorphous In-Ga-Zn-O (a-IGZO) are expected to be the channel material of TFTs in next-generation flat-panel displays because a-IGZO TFTs satisfy almost all the requirements for organic light-emitting-diode displays, large and fast liquid crystal and three-dimensional (3D) displays, which cannot be satisfied using conventional silicon and organic TFTs. The major insights of this review are summarized as follows. (i) Most device issues, such as uniformity, long-term stability against bias stress and TFT performance, are solved for a-IGZO TFTs. (ii) A sixth-generation (6G) process is demonstrated for 32″ and 37″ displays. (iii) An 8G sputtering apparatus and a sputtering target have been developed. (iv) The important effect of deep subgap states on illumination instability is revealed. (v) Illumination instability under negative bias has been intensively studied, and some mechanisms are proposed. (vi) Degradation mechanisms are classified into back-channel effects, the creation of traps at an interface and in the gate insulator, and the creation of donor states in annealed a-IGZO TFTs by the Joule heating; the creation of bulk defects should also be considered in the case of unannealed a-IGZO TFTs. (vii) Dense passivation layers improve the stability and photoresponse and are necessary for practical applications. (viii) Sufficient knowledge of electronic structures and electron transport in a-IGZO has been accumulated to construct device simulation models.

Microprocessor design for GaAs technology

NASA Astrophysics Data System (ADS)

Milutinovic, Veljko M.

Recent advances in the design of GaAs microprocessor chips are examined in chapters contributed by leading experts; the work is intended as reading material for a graduate engineering course or as a practical R&D reference. Topics addressed include the methodology used for the architecture, organization, and design of GaAs processors; GaAs device physics and circuit design; design concepts for microprocessor-based GaAs systems; a 32-bit GaAs microprocessor; a 32-bit processor implemented in GaAs JFET; and a direct coupled-FET-logic E/D-MESFET experimental RISC machine. Drawings, micrographs, and extensive circuit diagrams are provided.

Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template

NASA Astrophysics Data System (ADS)

Wang, Y. D.; Zang, K. Y.; Chua, S. J.; Tripathy, S.; Chen, P.; Fonstad, C. G.

2005-12-01

We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.

AlGaN/GaN High Electron Mobility Transistor-Based Biosensor for the Detection of C-Reactive Protein

PubMed Central

Lee, Hee Ho; Bae, Myunghan; Jo, Sung-Hyun; Shin, Jang-Kyoo; Son, Dong Hyeok; Won, Chul-Ho; Jeong, Hyun-Min; Lee, Jung-Hee; Kang, Shin-Won

2015-01-01

In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT)-based biosensor for the detection of C-reactive protein (CRP) using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region. PMID:26225981

GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates

NASA Astrophysics Data System (ADS)

Gutiérrez, M.; Lloret, F.; Jurczak, P.; Wu, J.; Liu, H. Y.; Araújo, D.

2018-05-01

The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

Special Technology Area Review on Displays. Report of Department of Defense Advisory Group on Electron Devices Working Group C (Electro-Optics)

DTIC Science & Technology

2004-03-01

mirror device ( DMD ) for C4ISR applications, the IBM 9.2 megapixel 22-in. diagonal active matrix liquid crystal display (AMLCD) monitor for data...FED, VFD, OLED and a variety of microdisplays (uD, comprising uLCD, uOLED, DMD and other MEMs) (see glossary). 3 CDT = cathode display tubes (used in...than SVGA, greater battery life and brightness, decreased weight and thickness, electromagnetic interference (EMI), and development of video

Current transport in graphene/AlGaN/GaN vertical heterostructures probed at nanoscale.

PubMed

Fisichella, Gabriele; Greco, Giuseppe; Roccaforte, Fabrizio; Giannazzo, Filippo

2014-08-07

Vertical heterostructures combining two or more graphene (Gr) layers separated by ultra-thin insulating or semiconductor barriers represent very promising systems for next generation electronics devices, due to the combination of high speed operation with wide-range current modulation by a gate bias. They are based on the specific mechanisms of current transport between two-dimensional-electron-gases (2DEGs) in close proximity. In this context, vertical devices formed by Gr and semiconductor heterostructures hosting an "ordinary" 2DEG can be also very interesting. In this work, we investigated the vertical current transport in Gr/Al(0.25)Ga(0.75)N/GaN heterostructures, where Gr is separated from a high density 2DEG by a ∼ 24 nm thick AlGaN barrier layer. The current transport from Gr to the buried 2DEG was characterized at nanoscale using conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM). From these analyses, performed both on Gr/AlGaN/GaN and on AlGaN/GaN reference samples using AFM tips with different metal coatings, the Gr/AlGaN Schottky barrier height ΦB and its lateral uniformity were evaluated, as well as the variation of the carrier densities of graphene (ngr) and AlGaN/GaN 2DEG (ns) as a function of the applied bias. A low Schottky barrier (∼ 0.40 eV) with excellent spatial uniformity was found at the Gr/AlGaN interface, i.e., lower compared to the measured values for metal/AlGaN contacts, which range from ∼ 0.6 to ∼ 1.1 eV depending on the metal workfunction. The electrical behavior of the Gr/AlGaN contact has been explained by Gr interaction with AlGaN donor-like surface states located in close proximity, which are also responsible of high n-type Gr doping (∼ 1.3 × 10(13) cm(-2)). An effective modulation of ns by the Gr Schottky contact was demonstrated by capacitance analysis under reverse bias. From this basic understanding of transport properties in Gr/AlGaN/GaN heterostructures, novel vertical field effect

A Laboratory-Based Course in Display Technology

ERIC Educational Resources Information Center

Sarik, J.; Akinwande, A. I.; Kymissis, I.

2011-01-01

A laboratory-based class in flat-panel display technology is presented. The course introduces fundamental concepts of display systems and reinforces these concepts through the fabrication of three display devices--an inorganic electroluminescent seven-segment display, a dot-matrix organic light-emitting diode (OLED) display, and a dot-matrix…

Three-dimensional hologram display system

NASA Technical Reports Server (NTRS)

Mintz, Frederick (Inventor); Chao, Tien-Hsin (Inventor); Bryant, Nevin (Inventor); Tsou, Peter (Inventor)

2009-01-01

The present invention relates to a three-dimensional (3D) hologram display system. The 3D hologram display system includes a projector device for projecting an image upon a display medium to form a 3D hologram. The 3D hologram is formed such that a viewer can view the holographic image from multiple angles up to 360 degrees. Multiple display media are described, namely a spinning diffusive screen, a circular diffuser screen, and an aerogel. The spinning diffusive screen utilizes spatial light modulators to control the image such that the 3D image is displayed on the rotating screen in a time-multiplexing manner. The circular diffuser screen includes multiple, simultaneously-operated projectors to project the image onto the circular diffuser screen from a plurality of locations, thereby forming the 3D image. The aerogel can use the projection device described as applicable to either the spinning diffusive screen or the circular diffuser screen.

Demonstration of β-(AlxGa1-x)2O3/Ga2O3 double heterostructure field effect transistors

NASA Astrophysics Data System (ADS)

Zhang, Yuewei; Joishi, Chandan; Xia, Zhanbo; Brenner, Mark; Lodha, Saurabh; Rajan, Siddharth

2018-06-01

In this work, we demonstrate modulation-doped β-(AlxGa1-x)2O3/Ga2O3 double heterostructure field effect transistors. The maximum sheet carrier density for a two-dimensional electron gas (2DEG) in a β-(AlxGa1-x)2O3/Ga2O3 heterostructure is limited by the conduction band offset and parasitic channel formation in the barrier layer. We demonstrate a double heterostructure to realize a β-(AlxGa1-x)2O3/Ga2O3/(AlxGa1-x)2O3 quantum well, where electrons can be transferred from below and above the β-Ga2O3 quantum well. The confined 2DEG charge density of 3.85 × 1012 cm-2 was estimated from the low-temperature Hall measurement, which is higher than that achievable in a single heterostructure. Hall mobilities of 1775 cm2/V.s at 40 K and 123 cm2/V.s at room temperature were measured. Modulation-doped double heterostructure field effect transistors showed a maximum drain current of IDS = 257 mA/mm, a peak transconductance (gm) of 39 mS/mm, and a pinch-off voltage of -7.0 V at room temperature. The three-terminal off-state breakdown measurement on the device with a gate-drain spacing (LGD) of 1.55 μm showed a breakdown voltage of 428 V, corresponding to an average breakdown field of 2.8 MV/cm. The breakdown measurement on the device with a scaled gate-drain spacing of 196 nm indicated an average breakdown field of 3.2 MV/cm. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 double heterostructure field effect transistor could act as a promising candidate for high power and high frequency device applications.

An Evaluation of Performance Characteristics of Primary Display Devices.

PubMed

Ekpo, Ernest U; McEntee, Mark F

2016-04-01

The aim of this study was to complete a full evaluation of the new EIZO RX850 liquid crystal display and compare it to two currently used medical displays in Australia (EIZO GS510 and Barco MDCG 5121). The American Association of Physicists in Medicine (AAPM) Task Group 18 Quality Control test pattern was used to assess the performance of three high-resolution primary medical displays: EIZO RX850, EIZO GS510, and Barco MDCG 5121. A Konica Minolta spectroradiometer (CS-2000) was used to assess luminance response, non-uniformity, veiling glare, and color uniformity. Qualitative evaluation of noise was also performed. Seven breast lesions were displayed on each monitor and photographed with a calibrated 5.5-MP Olympus E-1 digital SLR camera. ImageJ software was used to sample pixel information from each lesion and surrounding background to calculate their conspicuity index on each of the displays. All monitor fulfilled all AAPM acceptance criteria. The performance characteristics for EIZO RX850, Barco MDCG 5121, and EIZO GS510 respectively were as follows: maximum luminance (490, 500.5, and 413 cd/m(2)), minimum luminance (0.724, 1.170, and 0.92 cd/m(2)), contrast ratio (675:1, 428:1, 449:1), just-noticeable difference index (635, 622, 609), non-uniformity (20, 5.92, and 8.5 %), veiling glare (GR = 2465.6, 720.4, 1249.8), and color uniformity (Δu'v' = +0.003, +0.002, +0.002). All monitors demonstrated low noise levels. The conspicuity index (χ) of the lesions was slightly higher in the EIZO RX850 display. All medical displays fulfilled AAPM performance criteria, and performance characteristics of EIZO RX850 are equal to or better than those of the Barco MDCG 5121 and EIZO GS510 displays.

Growth of hierarchical GaN nanowires for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Raj, Rishabh; Vignesh, Veeramuthu; Ra, Yong-Ho; Nirmala, Rajkumar; Lee, Cheul-Ro; Navamathavan, Rangaswamy

2017-01-01

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Oxidation of GaAs substrates to enable β-Ga2O3 films for sensors and optoelectronic devices

NASA Astrophysics Data System (ADS)

Mao, Howard; Alhalaili, Badriyah; Kaya, Ahmet; Dryden, Daniel M.; Woodall, Jerry M.; Islam, M. Saif

2017-08-01

A very simple and inexpensive method for growing β-Ga2O3 films by heating GaAs wafers at high temperature in a furnace was found to contribute to large-area, high-quality β-Ga2O3 nanoscale thin films as well as nanowires depending on the growth conditions. We present the material characterization results including the optical band gap, Schottky barrier height with metal (gold), field ionization and photoconductance of β-Ga2O3 film and nanowires.

Polymer Dispersed Liquid Crystal Displays

NASA Astrophysics Data System (ADS)

Doane, J. William

The following sections are included: * INTRODUCTION AND HISTORICAL DEVELOPMENT * PDLC MATERIALS PREPARATION * Polymerization induced phase separation (PIPS) * Thermally induced phase separation (TIPS) * Solvent induced phase separation (SIPS) * Encapsulation (NCAP) * RESPONSE VOLTAGE * Dielectric and resistive effects * Radial configuration * Bipolar configuration * Other director configurations * RESPONSE TIME * DISPLAY CONTRAST * Light scattering and index matching * Incorporation of dyes * Contrast measurements * PDLC DISPLAY DEVICES AND INNOVATIONS * Reflective direct view displays * Large-scale, flexible displays * Switchable windows * Projection displays * High definition spatial light modulator * Haze-free PDLC shutters: wide angle view displays * ENVIRONMENTAL STABILITY * ACKNOWLEDGEMENTS * REFERENCES

GaN and ZnO nanostructures

NASA Astrophysics Data System (ADS)

Fündling, Sönke; Sökmen, Ünsal; Behrends, Arne; Al-Suleiman, Mohamed Aid Mansur; Merzsch, Stephan; Li, Shunfeng; Bakin, Andrey; Wehmann, Hergo-Heinrich; Waag, Andreas; Lähnemann, Jonas; Jahn, Uwe; Trampert, Achim; Riechert, Henning

2010-07-01

GaN and ZnO are both wide band gap semiconductors with interesting properties concerning optoelectronic and sensor device applications. Due to the lack or the high costs of native substrates, alternatives like sapphire, silicon, or silicon carbide are taken, but the resulting lattice and thermal mismatches lead to increased defect densities which reduce the material quality. In contrast, nanostructures with high aspect ratio have lower defect densities as compared to layers. In this work, we give an overview on our results achieved on both ZnO as well as GaN based nanorods. ZnO nanostructures were grown by a wet chemical approach as well as by VPT on different substrates - even on flexible polymers. To compare the growth results we analyzed the structures by XRD and PL and show possible device applications. The GaN nano- and microstructures were grown by metal organic vapor phase epitaxy either in a self- organized process or by selective area growth for a better control of shape and material composition. Finally we take a look onto possible device applications, presenting our attempts, e.g., to build LEDs based on GaN nanostructures.

Impact of rounded electrode corners on breakdown characteristics of AlGaN/GaN high-electron mobility transistors

NASA Astrophysics Data System (ADS)

Yamazaki, Taisei; Asubar, Joel T.; Tokuda, Hirokuni; Kuzuhara, Masaaki

2018-05-01

We investigated the impact of rounded electrode corners on the breakdown characteristics of AlGaN/GaN high-electron mobility transistors. For standard reference devices, catastrophic breakdown occurred predominantly near the sharp electrode corners. By introducing a rounded-electrode architecture, premature breakdown at the corners was mitigated. Moreover, the rate of breakdown voltage (V BR) degradation with an increasing gate width (W G) was significantly lower for devices with rounded corners. When W G was increased from 100 µm to 10 mm, the V BR of the reference device dropped drastically, from 1,200 to 300 V, whereas that of the rounded-electrode device only decreased to a respectable value of 730 V.

Double-heterojunction nanorod light-responsive LEDs for display applications.

PubMed

Oh, Nuri; Kim, Bong Hoon; Cho, Seong-Yong; Nam, Sooji; Rogers, Steven P; Jiang, Yiran; Flanagan, Joseph C; Zhai, You; Kim, Jae-Hwan; Lee, Jungyup; Yu, Yongjoon; Cho, Youn Kyoung; Hur, Gyum; Zhang, Jieqian; Trefonas, Peter; Rogers, John A; Shim, Moonsub

2017-02-10

Dual-functioning displays, which can simultaneously transmit and receive information and energy through visible light, would enable enhanced user interfaces and device-to-device interactivity. We demonstrate that double heterojunctions designed into colloidal semiconductor nanorods allow both efficient photocurrent generation through a photovoltaic response and electroluminescence within a single device. These dual-functioning, all-solution-processed double-heterojunction nanorod light-responsive light-emitting diodes open feasible routes to a variety of advanced applications, from touchless interactive screens to energy harvesting and scavenging displays and massively parallel display-to-display data communication. Copyright © 2017, American Association for the Advancement of Science.

Vertical GaN Devices for Power Electronics in Extreme Environments

DTIC Science & Technology

2016-03-31

electronics applications. In this paper vertical p-n diodes and transistors fabricated on pseudo bulk low defect density (104 to 106 cm-2) GaN substrates are...holes in p-GaN has deleterious effect on p-n junction behavior (Fig. 2), p-GaN contacts, and channel control in junction field-effect transistors at...and transistors ) utilizing p-n junctions are suitable for most practical applications including automotive (210K < T < 423K) but may have limitations

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

NASA Astrophysics Data System (ADS)

Perl, E. E.; Kuciauskas, D.; Simon, J.; Friedman, D. J.; Steiner, M. A.

2017-12-01

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 °C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 °C, we measure VOC that is ˜50 mV higher for the GaAs solar cell and ˜60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 °C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 °C to 400 °C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4× reduction in the effective lifetime and ˜40× increase in the surface recombination velocity as the temperature is increased from 25 °C to 400 °C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 °C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

DOE PAGES

Perl, E. E.; Kuciauskas, D.; Simon, J.; ...

2017-12-21

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

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

Perl, E. E.; Kuciauskas, D.; Simon, J.

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

7 CFR 1000.91-1000.92 - [Reserved

Code of Federal Regulations, 2010 CFR

2010-01-01

... 7 Agriculture 9 2010-01-01 2009-01-01 true [Reserved] 1000.91-1000.92 Section 1000.91-1000.92 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (Marketing... Miscellaneous Provisions §§ 1000.91-1000.92 [Reserved] ...

Oxygen-induced high diffusion rate of magnesium dopants in GaN/AlGaN based UV LED heterostructures.

PubMed

Michałowski, Paweł Piotr; Złotnik, Sebastian; Sitek, Jakub; Rosiński, Krzysztof; Rudziński, Mariusz

2018-05-23

Further development of GaN/AlGaN based optoelectronic devices requires optimization of the p-type material growth process. In particular, uncontrolled diffusion of Mg dopants may decrease the performance of a device. Thus it is meaningful to study the behavior of Mg and the origins of its diffusion in detail. In this work we have employed secondary ion mass spectrometry to study the diffusion of magnesium in GaN/AlGaN structures. We show that magnesium has a strong tendency to form Mg-H complexes which immobilize Mg atoms and restrain their diffusion. However, these complexes are not present in samples post-growth annealed in an oxygen atmosphere or Al-rich AlGaN structures which naturally have a high oxygen concentration. In these samples, more Mg atoms are free to diffuse and thus the average diffusion length is considerably larger than for a sample annealed in an inert atmosphere.

Investigation of the microstructure of metallic droplets on Ga(AsBi)/GaAs

NASA Astrophysics Data System (ADS)

Sterzer, E.; Knaub, N.; Ludewig, P.; Straubinger, R.; Beyer, A.; Volz, K.

2014-12-01

Low Bi content GaAs is a promising material for new optical devices with less heat production. The growth of such devices by metal organic vapor phase epitaxy faces several challenges. This paper summarizes results of the formation of metallic droplets during the epitaxial growth of Ga(AsBi) using all-liquid group III and V precursors. The samples that are grown, investigated by atomic force microscopy and scanning electron microscopy, show a different metal droplet distribution over the surface depending on the growth temperature and the V/III ratio of the precursors. Investigations with energy dispersive X-ray analysis and selective etching prove the appearance of phase separated Ga-Bi and pure Bi droplets at growth temperatures between 375 °C and 425 °C, which is explainable by the phase diagram of Ga-Bi. Since the pure Bi droplets show a preferred orientation on the surface after cool-down, transmission electron microscopy measurements were done by using the dark field imaging mode in addition to electron diffraction and high resolution imaging. These experiments show the single crystalline structure of the Bi droplets. The comparison of experimental diffraction patterns with image simulation shows a preferred alignment of Bi {10-1} lattice planes parallel to GaAs {202} lattice planes with the formation of a coincidence lattice. Thus it is possible to derive a model of how the Bi droplets evolve on the GaAs surface.

Influence of dislocations on indium diffusion in semi-polar InGaN/GaN heterostructures

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

Yin, Yao; National Institute for Materials Science, Tsukuba, Ibaraki 305-0044; Sun, Huabin

2015-05-15

The spatial distribution of indium composition in InGaN/GaN heterostructure is a critical topic for modulating the wavelength of light emitting diodes. In this letter, semi-polar InGaN/GaN heterostructure stripes were fabricated on patterned GaN/Sapphire substrates by epitaxial lateral overgrowth (ELO), and the spatial distribution of indium composition in the InGaN layer was characterized by using cathodoluminescence. It is found that the indium composition is mainly controlled by the diffusion behaviors of metal atoms (In and Ga) on the surface. The diffusivity of metal atoms decreases sharply as migrating to the region with a high density of dislocations and other defects, whichmore » influences the distribution of indium composition evidently. Our work is beneficial for the understanding of ELO process and the further development of InGaN/GaN heterostructure based devices.« less

Ohmic contact formation between metal and AlGaN/GaN heterostructure via graphene insertion

NASA Astrophysics Data System (ADS)

Sung Park, Pil; Reddy, Kongara M.; Nath, Digbijoy N.; Yang, Zhichao; Padture, Nitin P.; Rajan, Siddharth

2013-04-01

A simple method for the creation of Ohmic contact to 2D electron gas in AlGaN/GaN high electron-mobility transistors using Cr/graphene layer is demonstrated. A weak temperature dependence of this Ohmic contact observed in the range 77 to 300 K precludes thermionic emission or trap-assisted hopping as possible carrier-transport mechanisms. It is suggested that the Cr/graphene combination acts akin to a doped n-type semiconductor in contact with AlGaN/GaN heterostructure, and promotes carrier transport along percolating Al-lean paths through the AlGaN layer. This use of graphene offers a simple method for making Ohmic contacts to AlGaN/GaN heterostructures, circumventing complex additional processing steps involving high temperatures. These results could have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

Dual-functional on-chip AlGaAs/GaAs Schottky diode for RF power detection and low-power rectenna applications.

PubMed

Hashim, Abdul Manaf; Mustafa, Farahiyah; Rahman, Shaharin Fadzli Abd; Rahman, Abdul Rahim Abdul

2011-01-01

A Schottky diode has been designed and fabricated on an n-AlGaAs/GaAs high-electron-mobility-transistor (HEMT) structure. Current-voltage (I-V) measurements show good device rectification, with a Schottky barrier height of 0.4349 eV for Ni/Au metallization. The differences between the Schottky barrier height and the theoretical value (1.443 eV) are due to the fabrication process and smaller contact area. The RF signals up to 1 GHz are rectified well by the fabricated Schottky diode and a stable DC output voltage is obtained. The increment ratio of output voltage vs input power is 0.2 V/dBm for all tested frequencies, which is considered good enough for RF power detection. Power conversion efficiency up to 50% is obtained at frequency of 1 GHz and input power of 20 dBm with series connection between diode and load, which also shows the device's good potential as a rectenna device with further improvement. The fabricated n-AlGaAs/GaAs Schottky diode thus provides a conduit for breakthrough designs for RF power detectors, as well as ultra-low power on-chip rectenna device technology to be integrated in nanosystems.

GaAs core--shell nanowires for photovoltaic applications.

PubMed

Czaban, Josef A; Thompson, David A; LaPierre, Ray R

2009-01-01

We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

Ultrafast carrier dynamics in GaN/InGaN multiple quantum wells nanorods

NASA Astrophysics Data System (ADS)

Chen, Weijian; Wen, Xiaoming; Latzel, Michael; Yang, Jianfeng; Huang, Shujuan; Shrestha, Santosh; Patterson, Robert; Christiansen, Silke; Conibeer, Gavin

2018-01-01

GaN/InGaN multiple quantum wells (MQW) is a promising material for high-efficiency solid-state lighting. Ultrafast optical pump-probe spectroscopy is an important characterization technique for examining fundamental phenomena in semiconductor nanostructure with sub-picosecond resolution. In this study, ultrafast exciton and charge carrier dynamics in GaN/InGaN MQW planar layer and nanorod are investigated using femtosecond transient absorption (TA) techniques at room temperature. Here nanorods are fabricated by etching the GaN/InGaN MQW planar layers using nanosphere lithography and reactive ion etching. Photoluminescence efficiency of the nanorods have been proved to be much higher than that of the planar layers, but the mechanism of the nanorod structure improvement of PL efficiency is not adequately studied. By comparing the TA profile of the GaN/InGaN MQW planar layers and nanorods, the impact of surface states and nanorods lateral confinement in the ultrafast carrier dynamics of GaN/InGaN MQW is revealed. The nanorod sidewall surface states have a strong influence on the InGaN quantum well carrier dynamics. The ultrafast relaxation processes studied in this GaN/InGaN MQW nanostructure is essential for further optimization of device application.

New ultraportable display technology and applications

NASA Astrophysics Data System (ADS)

Alvelda, Phillip; Lewis, Nancy D.

1998-08-01

MicroDisplay devices are based on a combination of technologies rooted in the extreme integration capability of conventionally fabricated CMOS active-matrix liquid crystal display substrates. Customized diffraction grating and optical distortion correction technology for lens-system compensation allow the elimination of many lenses and systems-level components. The MicroDisplay Corporation's miniature integrated information display technology is rapidly leading to many new defense and commercial applications. There are no moving parts in MicroDisplay substrates, and the fabrication of the color generating gratings, already part of the CMOS circuit fabrication process, is effectively cost and manufacturing process-free. The entire suite of the MicroDisplay Corporation's technologies was devised to create a line of application- specific integrated circuit single-chip display systems with integrated computing, memory, and communication circuitry. Next-generation portable communication, computer, and consumer electronic devices such as truly portable monitor and TV projectors, eyeglass and head mounted displays, pagers and Personal Communication Services hand-sets, and wristwatch-mounted video phones are among the may target commercial markets for MicroDisplay technology. Defense applications range from Maintenance and Repair support, to night-vision systems, to portable projectors for mobile command and control centers.

High power cascaded mid-infrared InAs/GaSb light emitting diodes on mismatched GaAs

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

Provence, S. R., E-mail: sydney-provence@uiowa.edu; Ricker, R.; Aytac, Y.

2015-09-28

InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm{sup 2}-sr and 1.06 W/cm{sup 2}-sr for the 100 × 100 μm{sup 2} GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

Orthogonal interfacial exchange coupling in GaMnAsP/GaMnAs bilayers

NASA Astrophysics Data System (ADS)

Li, Xiang; Bac, Seul-Ki; Dong, Sining; Liu, Xinyu; Lee, Sanghoon; Rouvimov, Sergei; Dobrowolska, Margaret; Furdyna, Jacek K.

2018-05-01

We carried out a systematic study of magnetic ordering and magnetic interlayer coupling in Ga1-xMnxAs1-yPy/Ga1-xMnxAs bilayers using superconducting quantum interference device magnetometry and ferromagnetic resonance. Such bilayers are interesting, because the easy axis of the constituent materials are orthogonal. Our results show that the bilayers are strongly exchange-coupled at the interface, that manifests itself in the form of horizontal exchange-bias-like shifts of the hysteresis loops of the Ga1-xMnxAs layer, as observed in field-cooled magnetic measurements.

Significant performance enhancement of InGaN/GaN nanorod LEDs with multi-layer graphene transparent electrodes by alumina surface passivation

NASA Astrophysics Data System (ADS)

Latzel, M.; Büttner, P.; Sarau, G.; Höflich, K.; Heilmann, M.; Chen, W.; Wen, X.; Conibeer, G.; Christiansen, S. H.

2017-02-01

Nanotextured surfaces provide an ideal platform for efficiently capturing and emitting light. However, the increased surface area in combination with surface defects induced by nanostructuring e.g. using reactive ion etching (RIE) negatively affects the device’s active region and, thus, drastically decreases device performance. In this work, the influence of structural defects and surface states on the optical and electrical performance of InGaN/GaN nanorod (NR) light emitting diodes (LEDs) fabricated by top-down RIE of c-plane GaN with InGaN quantum wells was investigated. After proper surface treatment a significantly improved device performance could be shown. Therefore, wet chemical removal of damaged material in KOH solution followed by atomic layer deposition of only 10 {nm} alumina as wide bandgap oxide for passivation were successfully applied. Raman spectroscopy revealed that the initially compressively strained InGaN/GaN LED layer stack turned into a virtually completely relaxed GaN and partially relaxed InGaN combination after RIE etching of NRs. Time-correlated single photon counting provides evidence that both treatments—chemical etching and alumina deposition—reduce the number of pathways for non-radiative recombination. Steady-state photoluminescence revealed that the luminescent performance of the NR LEDs is increased by about 50% after KOH and 80% after additional alumina passivation. Finally, complete NR LED devices with a suspended graphene contact were fabricated, for which the effectiveness of the alumina passivation was successfully demonstrated by electroluminescence measurements.