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Sample records for algan quantum wells

  1. Enhancement of optical polarization degree of AlGaN quantum wells by using staggered structure.

    PubMed

    Wang, Weiying; Lu, Huimin; Fu, Lei; He, Chenguang; Wang, Mingxing; Tang, Ning; Xu, Fujun; Yu, Tongjun; Ge, Weikun; Shen, Bo

    2016-08-01

    Staggered AlGaN quantum wells (QWs) are designed to enhance the transverse-electric (TE) polarized optical emission in deep ultraviolet (DUV) light- emitting diodes (LED). The optical polarization properties of the conventional and staggered AlGaN QWs are investigated by a theoretical model based on the k·p method as well as polarized photoluminescence (PL) measurements. Based on an analysis of the valence subbands and momentum matrix elements, it is found that AlGaN QWs with step-function-like Al content in QWs offers much stronger TE polarized emission in comparison to that from conventional AlGaN QWs. Experimental results show that the degree of the PL polarization at room temperature can be enhanced from 20.8% of conventional AlGaN QWs to 40.2% of staggered AlGaN QWs grown by MOCVD, which is in good agreement with the theoretical simulation. It suggests that polarization band engineering via staggered AlGaN QWs can be well applied in high efficiency AlGaN-based DUV LEDs. PMID:27505782

  2. Capping green emitting (Ga,In)N quantum wells with (Al,Ga)N: impact on structural and optical properties

    NASA Astrophysics Data System (ADS)

    Hussain, Sakhawat; Lekhal, Kaddour; Kim-Chauveau, Hyonju; Vennéguès, Philippe; De Mierry, Philippe; Damilano, Benjamin

    2014-03-01

    The difference of growth temperatures between InGaN quantum wells and GaN barriers has detrimental effects on the properties of the wells. Different capping processes of InGaN quantum well with a thin AlGaN layer have been investigated to prevent these effects. Both structural and optical properties of the samples, grown on c-plane sapphire substrates by metalorganic vapor phase epitaxy, were studied through transmission electron microscopy (TEM), x-ray diffraction and room temperature photoluminescence. The average quantum well thickness and its indium composition were determined by digital processing of lattice fringes in cross-sectional TEM images. From the analysis of the well thickness distribution, it is shown that AlGaN as a capping layer helps to compensate an unwanted undulation at the upper InGaN QW-barrier interface. Moreover, when deposited at the same temperature as InGaN, the AlGaN layer is effective in avoiding or reducing the evaporation and/or diffusion of indium from InGaN wells, which results in the thinning of the well. It therefore helps to extend the emission wavelength up to 540 nm with a reduced degradation of the room temperature photoluminescence efficiency.

  3. Enhanced photoluminescence efficiency in AlGaN quantum wells with gradient-composition AlGaN barriers

    NASA Astrophysics Data System (ADS)

    Shevchenko, E. A.; Nechaev, D. V.; Jmerik, V. N.; Kaibyshev, V. Kh; Ivanov, S. V.; Toropov, A. A.

    2016-08-01

    We present photoluminescence studies of AIxGa1-xN/AlyGa1-yN (y = x+0.3) quantum well (QW) heterostructures with graded AI content in barrier layers, emitting in the range 285-315 nm. The best-established internal quantum efficiency of the QW emission is as high as 81% at 300 K, owing to enhanced activation energy of charge carriers and exciton binding energy in the QW heterostructure with optimized design.

  4. Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes

    SciTech Connect

    Mehnke, Frank Kuhn, Christian; Guttmann, Martin; Reich, Christoph; Kolbe, Tim; Rass, Jens; Wernicke, Tim; Kueller, Viola; Knauer, Arne; Lapeyrade, Mickael; Einfeldt, Sven; Weyers, Markus; Kneissl, Michael

    2014-08-04

    The design and Mg-doping profile of AlN/Al{sub 0.7}Ga{sub 0.3}N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm{sup 2}.

  5. Onset of surface stimulated emission at 260 nm from AlGaN multiple quantum wells

    SciTech Connect

    Li, Xiaohang E-mail: dupuis@gatech.edu; Xie, Hongen; Ponce, Fernando A.; Ryou, Jae-Hyun; Detchprohm, Theeradetch; Dupuis, Russell D. E-mail: dupuis@gatech.edu

    2015-12-14

    We demonstrated onset of deep-ultraviolet (DUV) surface stimulated emission (SE) from c-plane AlGaN multiple-quantum well (MQW) heterostructures grown on a sapphire substrate by optical pumping at room temperature. The onset of SE became observable at a pumping power density of 630 kW/cm{sup 2}. Spectral deconvolution revealed superposition of a linearly amplified spontaneous emission peak at λ ∼ 257.0 nm with a full width at half maximum (FWHM) of ∼12 nm and a superlinearly amplified SE peak at λ ∼ 260 nm with a narrow FWHM of less than 2 nm. In particular, the wavelength of ∼260 nm is the shortest wavelength of surface SE from III-nitride MQW heterostructures to date. Atomic force microscopy and scanning transmission electron microscopy measurements were employed to investigate the material and structural quality of the AlGaN heterostructures, showing smooth surface and sharp layer interfaces. This study offers promising results for AlGaN heterostructures grown on sapphire substrates for the development of DUV vertical cavity surface emitting lasers (VCSELs)

  6. Improved characteristics of ultraviolet AlGaN multiple-quantum-well laser diodes with step-graded quantum barriers close to waveguide layers

    NASA Astrophysics Data System (ADS)

    Cai, Xuefen; Li, Shuping; Kang, Junyong

    2016-09-01

    Ultraviolet AlGaN multiple-quantum-well laser diodes (LDs) with step-graded quantum barriers (QBs) instead of conventional first and last QBs close to waveguide layers are proposed. The characteristics of this type of laser diodes are numerically investigated by using the software PICS3D and it is found that the performances of these LDs are greatly improved. The results indicates that the structure with step-graded QBs exhibits higher output light power, slope efficiency and emission intensity, as well as lower series resistance and threshold current density under the identical condition, compared with conventional LD structure.

  7. High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates

    SciTech Connect

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramón; Xie, Jinqiao; Mita, Seiji

    2015-04-06

    The internal quantum efficiency (IQE) of Al{sub 0.55}Ga{sub 0.45}N/AlN and Al{sub 0.55}Ga{sub 0.45}N/Al{sub 0.85}Ga{sub 0.15}N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ∼80% at a carrier density of 10{sup 18 }cm{sup −3} was achieved at ∼258 nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures.

  8. Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes

    SciTech Connect

    Reich, Christoph Guttmann, Martin; Wernicke, Tim; Mehnke, Frank; Kuhn, Christian; Feneberg, Martin; Goldhahn, Rüdiger; Rass, Jens; Kneissl, Michael; Lapeyrade, Mickael; Einfeldt, Sven; Knauer, Arne; Kueller, Viola; Weyers, Markus

    2015-10-05

    The optical polarization of emission from ultraviolet (UV) light emitting diodes (LEDs) based on (0001)-oriented Al{sub x}Ga{sub 1−x}N multiple quantum wells (MQWs) has been studied by simulations and electroluminescence measurements. With increasing aluminum mole fraction in the quantum well x, the in-plane intensity of transverse-electric (TE) polarized light decreases relative to that of the transverse-magnetic polarized light, attributed to a reordering of the valence bands in Al{sub x}Ga{sub 1−x}N. Using k ⋅ p theoretical model calculations, the AlGaN MQW active region design has been optimized, yielding increased TE polarization and thus higher extraction efficiency for bottom-emitting LEDs in the deep UV spectral range. Using (i) narrow quantum wells, (ii) barriers with high aluminum mole fractions, and (iii) compressive growth on patterned aluminum nitride sapphire templates, strongly TE-polarized emission was observed at wavelengths as short as 239 nm.

  9. Localized surface plasmon-enhanced light emission using platinum nanorings in deep ultraviolet-emitting AlGaN quantum wells.

    PubMed

    Shin, Hee Woong; Son, Kyung Rock; Kim, Tae Geun

    2016-01-01

    We report the enhancement of deep ultraviolet emissions from AlGaN-based quantum wells (QWs) using energy-matched localized surface plasmons (LSPs) in platinum (Pt) nanoring arrays. The peak resonances of the extinction spectra were shifted to the red spectral region as the nanoring diameters increased, and the Pt nanorings with a diameter of 325 nm exhibited strong photoluminescence (PL) resonance at 279 nm. The emission enhancement ratio was calculated to be 304% in peak PL intensity when compared to that of the bare AlGaN QWs; this is attributed to the strong coupling of QWs with LSPs from the Pt nanorings.

  10. Statistical nanoscale study of localised radiative transitions in GaN/AlGaN quantum wells and AlGaN epitaxial layers

    NASA Astrophysics Data System (ADS)

    Rigutti, L.; Mancini, L.; Lefebvre, W.; Houard, J.; Hernàndez-Maldonado, D.; Di Russo, E.; Giraud, E.; Butté, R.; Carlin, J.-F.; Grandjean, N.; Blavette, D.; Vurpillot, F.

    2016-09-01

    Compositional disorder has important consequences on the optical properties of III-nitride ternary alloys. In AlGaN epilayers and AlGaN-based quantum heterostructures, the potential fluctuations induced by such disorder lead to the localisation of carriers at low temperature, which affects their transition energies. Using the correlations between micro-photoluminescence, scanning transmission electron microscopy and atom probe tomography we have analysed the optical behaviour of Al0.25Ga0.75N epilayers and that of GaN/AlGaN quantum wells, and reconstructed in three dimensions the distribution of chemical species with sub-nanometre spatial resolution. These composition maps served as the basis for the effective mass calculation of electrons and holes involved in radiative transitions. Good statistical predictions were subsequently obtained for the above-mentioned transition and localisation energies by establishing a link with their microstructural properties.

  11. Demonstration of transverse-magnetic deep-ultraviolet stimulated emission from AlGaN multiple-quantum-well lasers grown on a sapphire substrate

    SciTech Connect

    Li, Xiao-Hang E-mail: dupuis@gatech.edu; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D. E-mail: dupuis@gatech.edu; Wei, Yong O.; Wang, Shuo; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A.

    2015-01-26

    We demonstrate transverse-magnetic (TM) dominant deep-ultraviolet (DUV) stimulated emission from photo-pumped AlGaN multiple-quantum-well lasers grown pseudomorphically on an AlN/sapphire template by means of photoluminescence at room temperature. The TM-dominant stimulated emission was observed at wavelengths of 239, 242, and 243 nm with low thresholds of 280, 250, and 290 kW/cm{sup 2}, respectively. In particular, the lasing wavelength of 239 nm is shorter compared to other reports for AlGaN lasers grown on foreign substrates including sapphire and SiC. The peak wavelength difference between the transverse-electric (TE)-polarized emission and TM-polarized emission was approximately zero for the lasers in this study, indicating the crossover of crystal-field split-off hole and heavy-hole valence bands. The rapid variation of polarization between TE- and TM-dominance versus the change in lasing wavelength from 243 to 249 nm can be attributed to a dramatic change in the TE-to-TM gain coefficient ratio for the sapphire-based DUV lasers in the vicinity of TE-TM switch.

  12. Pressure Study of Photoluminescence in GaN/InGaN/ AlGaN Quantum Wells

    NASA Astrophysics Data System (ADS)

    Perlin, Piotr; Iota, V.; Weinstein, B. A.; Wisniewski, P.; Osinski, M.; Eliseev, P. G.

    1997-03-01

    We have studied the photoluminescence (PL) from two commercial high brightness single quantum well light emitting diodes (Nichia Chem. Industs.) with In_xGa_1-x N (x=0.45 and 0.2) as the active layers under hydrostatic pressures up to 7 GPa. These diodes are the best existing light emitters at short wavelengths, having the emission wavelengths of 430 nm and 530 nm depending on the content of indium in the 30 Åthick quantum wells. Although these devices show a remarkable quality and efficiency (luminosity as high as 12 cd), the mechanism of recombination remains obscure. We discovered that the pressure coefficient for each of the observed PL peaks is dramatically (2-3 times) lower than that of the energy gap of its InGaN active layer. These observations, in conjunction with the fact that the observed emission occurs below the energy gap of the quantum well material, and also considering the anomalous temperature behavior of the emission (peak energy increasing with temperature) suggest the involvement of localized states and exclude a simple band-to-band recombination picture. These localized states may be tentatively attributed to the presence of band tails in the gap which stem from composition fluctuations in the InGaN alloy. (figures)

  13. High-efficiency of AlInGaN/Al(In)GaN-delta AlGaN quantum wells for deep-ultraviolet emission

    NASA Astrophysics Data System (ADS)

    Saidi, Hosni; Ridene, Said

    2016-10-01

    Band structure and optical gain properties of AlInGaN/AlInGaN-delta-AlGaN quantum wells for deep-ultraviolet light emitting and lasers diodes with wavelength λ ∼229 nm and TE-polarized optical gain peak intensity ∼1.7 times larger than the conventional AlInN-delta-GaN was proposed and investigated in this work. The active region is made up of 20 Å staggered Al0.89In0.03Ga0.08N/Al0.8In 0.01Ga0.19N layers with a 3 Å Al0.46Ga0.54N delta layer. The use of the quaternary AlInGaN well layer permits the independent control of the band gap and the lattice parameter, so that the internal electric field induced by polarizations can be reduced and interband transition energy increases. Therefore, we can predict that the optical performance of the AlInGaN-delta-AlGaN is more convenient for an emission in the deep-ultraviolet than that of the conventional AlInN-delta-GaN-based quantum wells.

  14. Performance enhancement of blue light-emitting diodes with InGaN/GaN multi-quantum wells grown on Si substrates by inserting thin AlGaN interlayers

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeya; Yoshida, Hisashi; Uesugi, Kenjiro; Ito, Toshihide; Okada, Aoi; Nunoue, Shinya

    2016-09-01

    We have grown blue light-emitting diodes (LEDs) having InGaN/GaN multi-quantum wells (MQWs) with thin AlyGa1-yN (0 < y < 0.3) interlayers on Si(111) substrates. It was found by high-resolution transmission electron microscopy observations and three-dimensional atom probe analysis that 1-nm-thick interlayers with an AlN mole fraction of less than y = 0.3 were continuously formed between GaN barriers and InGaN wells, and that the AlN mole fraction up to y = 0.15 could be consistently controlled. The external quantum efficiency of the blue LED was enhanced in the low-current-density region (≤45 A/cm2) but reduced in the high-current-density region by the insertion of the thin Al0.15Ga0.85N interlayers in the MQWs. We also found that reductions in both forward voltage and wavelength shift with current were achieved by inserting the interlayers even though the inserted AlGaN layers had potential higher than that of the GaN barriers. The obtained peak wall-plug efficiency was 83% at room temperature. We suggest that the enhanced electroluminescence (EL) performance was caused by the introduction of polarization-induced hole carriers in the InGaN wells on the side adjacent to the thin AlGaN/InGaN interface and efficient electron carrier transport through multiple wells. This model is supported by temperature-dependent EL properties and band-diagram simulations. We also found that inserting the interlayers brought about a reduction in the Shockley-Read-Hall nonradiative recombination component, corresponding to the shrinkage of V-defects. This is another conceivable reason for the observed performance enhancement.

  15. Quantum chemical mechanism in parasitic reaction of AlGaN alloys formation

    NASA Astrophysics Data System (ADS)

    Makino, Osamu; Nakamura, Koichi; Tachibana, Akitomo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    2000-06-01

    The mechanism of parasitic reactions among trimethylaluminum (TMA), trimethylgallium (TMG), and NH 3 in atmospheric pressure (AP) MOVPE for growth of AlGaN is theoretically studied using the quantum chemical method. The calculations show that metal-nitrogen chain growth reaction easily proceeds through the successive reactions of 'complex formation with NH 3' and 'CH 4 elimination by the bimolecular mechanism'. Additionally, a parasitic reaction in APMOVPE using other raw material is also investigated. The calculated result shows that small change of raw material raises activation energy of parasitic reaction, and, thus, the parasitic reaction is suppressed. This result suggests a way to improve APMOVPE by a suitable choice of substituent.

  16. Handheld deep ultraviolet emission device based on aluminum nitride quantum wells and graphene nanoneedle field emitters.

    PubMed

    Matsumoto, Takahiro; Iwayama, Sho; Saito, Takao; Kawakami, Yasuyuki; Kubo, Fumio; Amano, Hiroshi

    2012-10-22

    We report the successful fabrication of a compact deep ultraviolet emission device via a marriage of AlGaN quantum wells and graphene nanoneedle field electron emitters. The device demonstrated a 20-mW deep ultraviolet output power and an approximately 4% power efficiency. The performance of this device may lead toward the realization of an environmentally friendly, convenient and practical deep ultraviolet light source.

  17. Wafer-scale crack-free AlGaN on GaN through two-step selective-area growth for optically pumped stimulated emission

    NASA Astrophysics Data System (ADS)

    Ko, Young-Ho; Bae, Sung-Bum; Kim, Sung-Bock; Kim, Dong Churl; Leem, Young Ahn; Cho, Yong-Hoon; Nam, Eun-Soo

    2016-07-01

    Crack-free AlGaN template has been successfully grown over entire 2-in. wafer by using 2-step selective-area growth (SAG). The GaN truncated structure was obtained by vertical growth mode with low growth temperature. AlGaN of second step was grown under lateral growth mode. Low pressure enhanced the relative ratio of lateral to vertical growth rate as well as absolute overall growth rate. High V/III ratio was favorable for lateral growth mode. Crack-free planar AlGaN was obtained under low pressure of 30 Torr and high V/III ratio of 4400. The AlGaN was crack-free over entire 2-in. wafer and had quite uniform Al-mole fraction. The dislocation density of the AlGaN with 20% Al-composition was as low as ~7.6×108 /cm2, measured by cathodoluminescence. GaN/AlGaN multi-quantum well (MQW) with cladding and waveguide layers were grown on the crack-free AlGaN template with low dislocation density. It was confirmed that the MQW on the AlGaN template emitted the stimulated emission at 355.5 nm through optical pumping experiment. The AlGaN obtained by 2-step SAG would provide high crystal quality for highly-efficient optoelectronic devices as well as the ultraviolet laser diode.

  18. Quantum well multijunction photovoltaic cell

    DOEpatents

    Chaffin, Roger J.; Osbourn, Gordon C.

    1987-01-01

    A monolithic, quantum well, multilayer photovoltaic cell comprises a p-n junction comprising a p-region on one side and an n-region on the other side, each of which regions comprises a series of at least three semiconductor layers, all p-type in the p-region and all n-type in the n-region; each of said series of layers comprising alternating barrier and quantum well layers, each barrier layer comprising a semiconductor material having a first bandgap and each quantum well layer comprising a semiconductor material having a second bandgap when in bulk thickness which is narrower than said first bandgap, the barrier layers sandwiching each quantum well layer and each quantum well layer being sufficiently thin that the width of its bandgap is between said first and second bandgaps, such that radiation incident on said cell and above an energy determined by the bandgap of the quantum well layers will be absorbed and will produce an electrical potential across said junction.

  19. Quantum well multijunction photovoltaic cell

    DOEpatents

    Chaffin, R.J.; Osbourn, G.C.

    1983-07-08

    A monolithic, quantum well, multilayer photovoltaic cell comprises a p-n junction comprising a p-region on one side and an n-region on the other side, each of which regions comprises a series of at least three semiconductor layers, all p-type in the p-region and all n-type in the n-region; each of said series of layers comprising alternating barrier and quantum well layers, each barrier layer comprising a semiconductor material having a first bandgap and each quantum well layer comprising a semiconductor material having a second bandgap when in bulk thickness which is narrower than said first bandgap, the barrier layers sandwiching each quantum well layer and each quantum well layer being sufficiently thin that the width of its bandgap is between said first and second bandgaps, such that radiation incident on said cell and above an energy determined by the bandgap of the quantum well layers will be absorbed and will produce an electrical potential across said junction.

  20. Measurement and simulation of top- and bottom-illuminated solar-blind AlGaN metal-semiconductor-metal photodetectors with high external quantum efficiencies

    SciTech Connect

    Brendel, Moritz Helbling, Markus; Knigge, Andrea; Brunner, Frank; Weyers, Markus

    2015-12-28

    A comprehensive study on top- and bottom-illuminated Al{sub 0.5}Ga{sub 0.5}N/AlN metal-semiconductor-metal (MSM) photodetectors having different AlGaN absorber layer thickness is presented. The measured external quantum efficiency (EQE) shows pronounced threshold and saturation behavior as a function of applied bias voltage up to 50 V reaching about 50% for 0.1 μm and 67% for 0.5 μm thick absorber layers under bottom illumination. All experimental findings are in very good accordance with two-dimensional drift-diffusion modeling results. By taking into account macroscopic polarization effects in the hexagonal metal-polar +c-plane AlGaN/AlN heterostructures, new insights into the general device functionality of AlGaN-based MSM photodetectors are obtained. The observed threshold/saturation behavior is caused by a bias-dependent extraction of photoexcited holes from the Al{sub 0.5}Ga{sub 0.5}N/AlN interface. While present under bottom illumination for any AlGaN layer thickness, under top illumination this mechanism influences the EQE-bias characteristics only for thin layers.

  1. N-polar III-nitride quantum well light-emitting diodes with polarization-induced doping

    SciTech Connect

    Verma, Jai; Simon, John; Protasenko, Vladimir; Kosel, Thomas; Xing, Huili Grace; Jena, Debdeep

    2011-10-24

    Nitrogen-polar III-nitride heterostructures present unexplored advantages over Ga(metal)-polar crystals for optoelectronic devices. This work reports N-polar III-nitride quantum-well ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy that integrate polarization-induced p-type doping by compositional grading from GaN to AlGaN along N-face. The graded AlGaN layer simultaneously acts as an electron blocking layer while facilitating smooth injection of holes into the active region, while the built-in electric field in the barriers improves carrier injection into quantum wells. The enhanced doping, carrier injection, and light extraction indicate that N-polar structures have the potential to exceed the performance of metal-polar ultraviolet light-emitting diodes.

  2. Quantum-Well Thermophotovoltaic Cells

    NASA Technical Reports Server (NTRS)

    Freudlich, Alex; Ignatiev, Alex

    2009-01-01

    Thermophotovoltaic cells containing multiple quantum wells have been invented as improved means of conversion of thermal to electrical energy. The semiconductor bandgaps of the quantum wells can be tailored to be narrower than those of prior thermophotovoltaic cells, thereby enabling the cells to convert energy from longer-wavelength photons that dominate the infrared-rich spectra of typical thermal sources with which these cells would be used. Moreover, in comparison with a conventional single-junction thermophotovoltaic cell, a cell containing multiple narrow-bandgap quantum wells according to the invention can convert energy from a wider range of wavelengths. Hence, the invention increases the achievable thermal-to-electrical energy-conversion efficiency. These thermophotovoltaic cells are expected to be especially useful for extracting electrical energy from combustion, waste-heat, and nuclear sources having temperatures in the approximate range from 1,000 to 1,500 C.

  3. Tunable quantum well infrared detector

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph (Inventor)

    1990-01-01

    A novel infrared detector (20, 20', 20), is provided, which is characterized by photon-assisted resonant tunneling between adjacent quantum wells (22a, 22b) separated by barrier layers (28) in an intrinsic semiconductor layer (24) formed on an n.sup.+ substrate (26), wherein the resonance is electrically tunable over a wide band of wavelengths in the near to long infrared region. An n.sup.+ contacting layer (34) is formed over the intrinsic layer and the substrate is n.sup.+ doped to provide contact to the quantum wells. The detector permits fabrication of arrays (30) (one-dimensional and two-dimensional) for use in imaging and spectroscopy applications.

  4. Stimulated emission at 288 nm from silicon-doped AlGaN-based multiple-quantum-well laser.

    PubMed

    Tian, Yingdong; Yan, Jianchang; Zhang, Yun; Chen, Xiang; Guo, Yanan; Cong, Peipei; Sun, Lili; Wang, Qinjin; Guo, Enqing; Wei, Xuecheng; Wang, Junxi; Li, Jinmin

    2015-05-01

    We demonstrated stimulated emission at 288 nm from a silicon-doped AlGaN-based multiple-quantum-well (MQW) ultraviolet (UV) laser grown on sapphire. The optical pumping threshold energy density of the UV laser was 64 mJ/cm2, while lasing behavior was not observed in undoped AlGaN MQWs. This means silicon doping could effectively reduce the lasing threshold of UV lasers, and the mechanism was studied showing that the silicon-doped AlGaN MQWs had a 41% higher internal quantum efficiency (IQE) compared with the undoped one. The transmission electron microscopy characterization showed that silicon doping explicitly improved the crystallographic quality of MQWs. Calculation of the polarization charge in the MQWs further revealed that the advantage of better structure quality outweighed the reduction of internal polarization field by Si doping for the IQE enhancement and successful stimulated emission.

  5. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    SciTech Connect

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N.; Wang, X. Q. Shen, B.; Fu, K.; Zhang, B. S.; Hashimoto, H.; Yoshikawa, A.; Ge, W. K.

    2014-04-28

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection.

  6. Quantum Well Infrared Photodetectors (QWIP)

    NASA Technical Reports Server (NTRS)

    Levine, B. F.

    1990-01-01

    There has been a lot of interest in III-V long wavelength detectors in the lambda = 8 to 12 micron spectral range as alternatives to HgCdTe. Recently high performance quantum well infrared photodetectors (QWIP) have been demonstrated. They have a responsivity of R = 1.2 A/W, and a detectivity D(exp asterisk) sub lambda = 2 times 10(exp 10) cm Hz(exp 1/2)/W at 68 K for a QWIP with a cutoff wavelength of lambda sub c = 10.7 micron and a R = 1.0 A/W, and D(exp asterisk) sub lambda = 2 times 10(exp 10) cm Hz(exp 1/2)/W at T = 77 K for lambda sub c = 8.4 micron. These detectors consist of 50 periods of molecular beam epitaxy (MBE) grown layers doped n = 1 times 10(exp 18)cm(exp -3) having GaAs quantum well widths of 40 A and barrier widths of 500 A of Al sub x Ga sub 1-x As. Due to the well-established GaAs growth and processing techniques, these detectors have the potential for large, highly uniform, low cost, high performance arrays as well as monolithic integration with GaAs electronics, high speed and radiation hardness. Latest results on the transport physics, device performance and arrays are discussed.

  7. Excitons in asymmetric quantum wells

    NASA Astrophysics Data System (ADS)

    Grigoryev, P. S.; Kurdyubov, A. S.; Kuznetsova, M. S.; Ignatiev, I. V.; Efimov, Yu. P.; Eliseev, S. A.; Petrov, V. V.; Lovtcius, V. A.; Shapochkin, P. Yu.

    2016-09-01

    Resonance dielectric response of excitons is studied for the high-quality InGaAs/GaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances. A standard approach for the phenomenological analysis of the profiles is generalized by introducing different phase shifts for the light waves reflected from the QWs at different exciton resonances. Good agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to reliably obtain parameters of the exciton resonances: the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of the Schrödinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs.

  8. Silicon Germanium Quantum Well Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Davidson, Anthony Lee, III

    Today's growing energy demands require new technologies to provide high efficiency clean energy. Thermoelectrics that convert heat to electrical energy directly can provide a method for the automobile industry to recover waste heat to power vehicle electronics, hence improving fuel economy. If large enough efficiencies can be obtained then the internal combustion engine could even be replaced. Exhaust temperature for automotive application range from 400 to 800 K. In this temperature range the current state of the art materials are bulk Si1-xGex alloys. By alternating layers of Si and Si1-xGex alloy device performance may be enhanced through quantum well effects and variations in material thermal properties. In this study, superlattices designed for in-plane operation with varying period and crystallinity are examined to determine the effect on electrical and thermal properties. In-plane electrical resistivity of these materials was found to be below the bulk material at a similar doping at room temperature, confirming the role of quantum wells in electron transport. As period is reduced in the structures boundary scattering limits electron propagation leading to increased resistivity. The Seebeck coefficient measured at room temperature is higher than the bulk material, additionally lending proof to the effects of quantum wells. When examining cross-plane operation the low doping in the Si layers of the device produce high resistivity resulting from boundary scattering. Thermal conductivity was measured from 77 K up to 674 K and shows little variation due to periodicity and temperature, however an order of magnitude reduction over bulk Si1-xGex is shown in all samples. A model is developed that suggests a combination of phonon dispersion effects and strong boundary scattering. Further study of the phonon dispersion effects was achieved through the examination of the heat capacity by combining thermal diffusivity with thermal conductivity. All superlattices show a

  9. Ultra Thin Quantum Well Materials

    SciTech Connect

    Dr Saeid Ghamaty

    2012-08-16

    This project has enabled Hi-Z technology Inc. (Hi-Z) to understand how to improve the thermoelectric properties of Si/SiGe Quantum Well Thermoelectric Materials. The research that was completed under this project has enabled Hi-Z Technology, Inc. (Hi-Z) to satisfy the project goal to understand how to improve thermoelectric conversion efficiency and reduce costs by fabricating ultra thin Si/SiGe quantum well (QW) materials and measuring their properties. In addition, Hi-Z gained critical new understanding on how thin film fabrication increases the silicon substrate's electrical conductivity, which is important new knowledge to develop critical material fabrication parameters. QW materials are constructed with alternate layers of an electrical conductor, SiGe and an electrical insulator, Si. Film thicknesses were varied, ranging from 2nm to 10nm where 10 nm was the original film thickness prior to this work. The optimum performance was determined at a Si and SiGe thickness of 4nm for an electrical current and heat flow parallel to the films, which was an important conclusion of this work. Essential new information was obtained on how the Si substrate electrical conductivity increases by up to an order of magnitude upon deposition of QW films. Test measurements and calculations are accurate and include both the quantum well and the substrate. The large increase in substrate electrical conductivity means that a larger portion of the electrical current passes through the substrate. The silicon substrate's increased electrical conductivity is due to inherent impurities and thermal donors which are activated during both molecular beam epitaxy and sputtering deposition of QW materials. Hi-Z's forward looking cost estimations based on future high performance QW modules, in which the best Seebeck coefficient and electrical resistivity are taken from separate samples predict that the electricity cost produced with a QW module could be achieved at <$0.35/W. This price would

  10. Large TE polarized optical gain from AlInN-delta-GaN quantum well for ultraviolet lasers

    NASA Astrophysics Data System (ADS)

    Liu, Cheng; Ooi, Yu Kee; Zhang, Jing

    2016-03-01

    Ultraviolet (UV) lasers with wavelength (λ) < 300 nm have important applications in free-space communication, water/air purification, and biochemical agent detection. Conventionally, AlGaN quantum wells (QWs) are widely used as active region for UV lasers. However, high-efficiency electrically injected mid-UV lasers with λ ~ 250-300 nm are still very challenging as the corresponding AlGaN QWs suffer from severe band-mixing effect due to the presence of the valence sub-band crossover between the heavy-hole (HH) and crystal-field split off (CH) sub-bands, which would result in very low optical gain in such wavelength regime. Therefore, in this work, we propose and investigate the use of AlInN material system as an alternative for mid-UV lasers. Nanostructure engineering by the use of AlInN-delta-GaN QW has been performed to enable dominant conduction band - HH sub-band transition as well as optimized electron-hole wave function overlap. The insertion of the ultra-thin delta-GaN layer, which is lattice-matched to Al0.82In0.18N layer, would localize the wave functions strongly toward the center of the active region, leading to large transverse electric (TE) polarized optical gain (gTE) for λ~ 250- 300 nm. From our finding, the use of AlInN-delta-GaN QW resulted in ~ 3-times enhancement in TE-polarized optical gain, in comparison to that of conventional AlGaN QW, for gain media emitting at ~ 255 nm. The peak emission wavelength can be tuned by varying the delta layer thickness while maintaining large TE gain. Specifically, gTE ~ 3700 cm-1 was obtained for λ ~ 280-300 nm, which are very challenging for conventional AlGaN QW active region.

  11. Angular distribution of polarized light and its effect on light extraction efficiency in AlGaN deep-ultraviolet light-emitting diodes.

    PubMed

    Chen, Xinjuan; Ji, Cheng; Xiang, Yong; Kang, Xiangning; Shen, Bo; Yu, Tongjun

    2016-05-16

    Angular distribution of polarized light and its effect on light extraction efficiency (LEE) in AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) are investigated in this paper. A united picture is presented to describe polarized light's emission and propagation processes. It is found that the electron-hole recombinations in AlGaN multiple quantum wells produce three kinds of angularly distributed polarized emissions and propagation process can change their intensity distributions. By investigation the change of angular distributions in 277nm and 215nm LEDs, this work reveals that LEE can be significantly enhanced by modulating the angular distributions of polarized light of DUV LEDs.

  12. Quantum dots as active material for quantum cascade lasers: comparison to quantum wells

    NASA Astrophysics Data System (ADS)

    Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian

    2016-03-01

    We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.

  13. Ultrabroad stimulated emission from quantum well laser

    SciTech Connect

    Wang, Huolei; Zhou, Xuliang; Yu, Hongyan; Mi, Junping; Wang, Jiaqi; Bian, Jing; Wang, Wei; Pan, Jiaoqing; Ding, Ying; Chen, Weixi

    2014-06-23

    Observation of ultrabroad stimulated emission from a simplex quantum well based laser at the center wavelength of 1.06 μm is reported. With increased injection current, spectrum as broad as 38 nm and a pulsed output power of ∼50 mW have been measured. The experiments show evidence of an unexplored broad emission regime in the InGaAs/GaAs quantum well material system, which still needs theoretical modeling and further analysis.

  14. Formation and characteristics of AlGaN-based three-dimensional hexagonal nanopyramid semi-polar multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Tian, Yingdong; Yan, Jianchang; Zhang, Yun; Zhang, Yonghui; Chen, Xiang; Guo, Yanan; Wang, Junxi; Li, Jinmin

    2016-05-01

    We demonstrated for the first time the formation and study of semi-polar AlGaN multiple-quantum-wells (MQWs) grown on highly regular hexagonal AlN nanopyramids. The AlN nanopyramids were obtained by a metal-organic chemical vapor phase deposition regrowth method on a well-ordered AlN nanorod array prepared by a top-down etching process. The growth mechanism of the AlN nanopyramids was ascribed to the slow growth of the (101&cmb.macr;1) semi-polar plane, which resulted from hydrogen passivation. Beneath the semi-polar facets, air voids were formed. This was attributed to the insufficient delivery of gas reactants to the bottom of the nanorods during the growth process. The polarization effect in semi-polar AlGaN MQWs was numerically calculated. The results showed that the internal electric field (IEF) in the semi-polar MQWs was remarkably reduced by 80% in comparison with c-plane MQWs. Power dependent photoluminescence indicated that the semi-polar AlGaN MQWs had negligible wavelength shifts that resulted from the reduced IEF, which was in accordance with theoretical predictions. In addition, epitaxial strain was greatly relieved in the AlN regrowth layer, which was revealed from the peak shift of the E2(high) phonon using micro-Raman spectroscopy. The advantages of AlGaN-based hexagonal nanopyramid semi-polar three dimensional nanostructures would lead to a large improvement of output power in UV-LEDs.

  15. Formation and characteristics of AlGaN-based three-dimensional hexagonal nanopyramid semi-polar multiple quantum wells.

    PubMed

    Tian, Yingdong; Yan, Jianchang; Zhang, Yun; Zhang, Yonghui; Chen, Xiang; Guo, Yanan; Wang, Junxi; Li, Jinmin

    2016-06-01

    We demonstrated for the first time the formation and study of semi-polar AlGaN multiple-quantum-wells (MQWs) grown on highly regular hexagonal AlN nanopyramids. The AlN nanopyramids were obtained by a metal-organic chemical vapor phase deposition regrowth method on a well-ordered AlN nanorod array prepared by a top-down etching process. The growth mechanism of the AlN nanopyramids was ascribed to the slow growth of the (101[combining macron]1) semi-polar plane, which resulted from hydrogen passivation. Beneath the semi-polar facets, air voids were formed. This was attributed to the insufficient delivery of gas reactants to the bottom of the nanorods during the growth process. The polarization effect in semi-polar AlGaN MQWs was numerically calculated. The results showed that the internal electric field (IEF) in the semi-polar MQWs was remarkably reduced by 80% in comparison with c-plane MQWs. Power dependent photoluminescence indicated that the semi-polar AlGaN MQWs had negligible wavelength shifts that resulted from the reduced IEF, which was in accordance with theoretical predictions. In addition, epitaxial strain was greatly relieved in the AlN regrowth layer, which was revealed from the peak shift of the E2(high) phonon using micro-Raman spectroscopy. The advantages of AlGaN-based hexagonal nanopyramid semi-polar three dimensional nanostructures would lead to a large improvement of output power in UV-LEDs. PMID:27174102

  16. Photovoltaic driven multiple quantum well optical modulator

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph (Inventor)

    1990-01-01

    Multiple quantum well (MQW) structures (12) are utilized to provide real-time, reliable, high-performance, optically-addressed spatial-light modulators (SLM) (10). The optically-addressed SLM comprises a vertical stack of quantum well layers (12a) within the penetration depth of an optical write signal 18, a plurality of space charge barriers (12b) having predetermined tunneling times by control of doping and thickness. The material comprising the quantum well layers has a lower bandgap than that of the space charge barrier layers. The write signal modulates a read signal (20). The modulation sensitivity of the device is high and no external voltage source is required. In a preferred embodiment, the SLM having interleaved doped semiconductor layers for driving the MQW photovoltaically is characterized by the use of a shift analogous to the Moss-Burnstein shift caused by the filling of two-dimensional states in the multiple quantum wells, thus allowing high modulation sensitivity in very narrow wells. Arrays (30) may be formed with a plurality of the modulators.

  17. Fractional quantum conductance in edge channels of silicon quantum wells

    SciTech Connect

    Bagraev, Nikolay; Klyachkin, Leonid; Kudryavtsev, Andrey; Malyarenko, Anna

    2013-12-04

    We present the findings for the fractional quantum conductance of holes that is caused by the edge channels in the silicon nanosandwich prepared within frameworks of the Hall geometry. This nanosandwich represents the ultra-narrow p-type silicon quantum well (Si-QW), 2 nm, confined by the δ-barriers heavily doped with boron on the n-type Si (100) surface. The edge channels in the Si-QW plane are revealed by measuring the longitudinal quantum conductance staircase, G{sub xx}, as a function of the voltage applied to the Hall contacts, V{sub xy}, to a maximum of 4e{sup 2}/h. In addition to the standard plateau, 2e{sup 2}/h, the variations of the V{sub xy} voltage appear to exhibit the fractional form of the quantum conductance staircase with the plateaus and steps that bring into correlation respectively with the odd and even fractions.

  18. Spectroscopy of GaAs quantum wells

    SciTech Connect

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

  19. Infrared Multiple-Quantum-Well Phototransistor

    NASA Technical Reports Server (NTRS)

    Borenstain, Shmuel I.

    1992-01-01

    Proposed npn AlxGa1-xAs phototransistor incorporates multiple-quantum-well (MQW) infrared photodetector. Has n-doped contacts and is embedded between p-doped base region and n-doped collector region of transistor. Photocurrent amplified, and dark current suppressed.

  20. An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: Preferential outcoupling of strong in-plane emission

    PubMed Central

    Lee, Jong Won; Kim, Dong Yeong; Park, Jun Hyuk; Schubert, E. Fred; Kim, Jungsub; Lee, Jinsub; Kim, Yong-Il; Park, Youngsoo; Kim, Jong Kyu

    2016-01-01

    While there is an urgent need for semiconductor-based efficient deep ultraviolet (DUV) sources, the efficiency of AlGaN DUV light-emitting diodes (LEDs) remains very low because the extraction of DUV photons is significantly limited by intrinsic material properties of AlGaN. Here, we present an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes for maximizing the power conversion efficiency. PMID:26935402

  1. An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: Preferential outcoupling of strong in-plane emission

    NASA Astrophysics Data System (ADS)

    Lee, Jong Won; Kim, Dong Yeong; Park, Jun Hyuk; Schubert, E. Fred; Kim, Jungsub; Lee, Jinsub; Kim, Yong-Il; Park, Youngsoo; Kim, Jong Kyu

    2016-03-01

    While there is an urgent need for semiconductor-based efficient deep ultraviolet (DUV) sources, the efficiency of AlGaN DUV light-emitting diodes (LEDs) remains very low because the extraction of DUV photons is significantly limited by intrinsic material properties of AlGaN. Here, we present an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes for maximizing the power conversion efficiency.

  2. An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: Preferential outcoupling of strong in-plane emission.

    PubMed

    Lee, Jong Won; Kim, Dong Yeong; Park, Jun Hyuk; Schubert, E Fred; Kim, Jungsub; Lee, Jinsub; Kim, Yong-Il; Park, Youngsoo; Kim, Jong Kyu

    2016-01-01

    While there is an urgent need for semiconductor-based efficient deep ultraviolet (DUV) sources, the efficiency of AlGaN DUV light-emitting diodes (LEDs) remains very low because the extraction of DUV photons is significantly limited by intrinsic material properties of AlGaN. Here, we present an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes for maximizing the power conversion efficiency. PMID:26935402

  3. An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: Preferential outcoupling of strong in-plane emission.

    PubMed

    Lee, Jong Won; Kim, Dong Yeong; Park, Jun Hyuk; Schubert, E Fred; Kim, Jungsub; Lee, Jinsub; Kim, Yong-Il; Park, Youngsoo; Kim, Jong Kyu

    2016-03-03

    While there is an urgent need for semiconductor-based efficient deep ultraviolet (DUV) sources, the efficiency of AlGaN DUV light-emitting diodes (LEDs) remains very low because the extraction of DUV photons is significantly limited by intrinsic material properties of AlGaN. Here, we present an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes for maximizing the power conversion efficiency.

  4. Semiconductor Lasers Containing Quantum Wells in Junctions

    NASA Technical Reports Server (NTRS)

    Yang, Rui Q.; Qiu, Yueming

    2004-01-01

    In a recent improvement upon In(x)Ga(1-x)As/InP semiconductor lasers of the bipolar cascade type, quantum wells are added to Esaki tunnel junctions, which are standard parts of such lasers. The energy depths and the geometric locations and thicknesses of the wells are tailored to exploit quantum tunneling such that, as described below, electrical resistances of junctions and concentrations of dopants can be reduced while laser performances can be improved. In(x)Ga(1-x)As/InP bipolar cascade lasers have been investigated as sources of near-infrared radiation (specifically, at wavelengths of about 980 and 1,550 nm) for photonic communication systems. The Esaki tunnel junctions in these lasers have been used to connect adjacent cascade stages and to enable transport of charge carriers between them. Typically, large concentrations of both n (electron-donor) and p (electron-acceptor) dopants have been necessary to impart low electrical resistances to Esaki tunnel junctions. Unfortunately, high doping contributes free-carrier absorption, thereby contributing to optical loss and thereby, further, degrading laser performance. In accordance with the present innovation, quantum wells are incorporated into the Esaki tunnel junctions so that the effective heights of barriers to quantum tunneling are reduced (see figure).

  5. An electrically injected AlGaN nanowire laser operating in the ultraviolet-C band

    SciTech Connect

    Zhao, S.; Liu, X.; Kang, J.; Mi, Z.; Woo, S. Y.; Botton, G. A.

    2015-07-27

    We have investigated the molecular beam epitaxial growth and characterization of nearly defect-free AlGaN nanowire heterostructures grown directly on Si substrate. By exploiting the Anderson localization of light, we have demonstrated electrically injected AlGaN nanowire lasers that can operate at 262.1 nm. The threshold current density is 200 A/cm{sup 2} at 77 K. The relatively low threshold current is attributed to the high Q-factor of the random cavity and the three-dimensional quantum confinement offered by the atomic-scale composition modulation in self-organized AlGaN nanowires.

  6. Strained quantum well photovoltaic energy converter

    NASA Technical Reports Server (NTRS)

    Freundlich, Alexandre (Inventor); Renaud, Philippe (Inventor); Vilela, Mauro Francisco (Inventor); Bensaoula, Abdelhak (Inventor)

    1998-01-01

    An indium phosphide photovoltaic cell is provided where one or more quantum wells are introduced between the conventional p-conductivity and n-conductivity indium phosphide layer. The approach allows the cell to convert the light over a wider range of wavelengths than a conventional single junction cell and in particular convert efficiently transparency losses of the indium phosphide conventional cell. The approach hence may be used to increase the cell current output. A method of fabrication of photovoltaic devices is provided where ternary InAsP and InGaAs alloys are used as well material in the quantum well region and results in an increase of the cell current output.

  7. Fractional Quantum Hall States in a Ge Quantum Well

    NASA Astrophysics Data System (ADS)

    Mironov, O. A.; d'Ambrumenil, N.; Dobbie, A.; Leadley, D. R.; Suslov, A. V.; Green, E.

    2016-04-01

    Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a SiGe /(001 )Si substrate in the quantum Hall regime are reported. We analyze the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long-range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarized Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required.

  8. Energy loss rate in disordered quantum well

    SciTech Connect

    Tripathi, P.; Ashraf, S. S. Z.; Hasan, S. T.; Sharma, A. C.

    2014-04-24

    We report the effect of dynamically screened deformation potential on the electron energy loss rate in disordered semiconductor quantum well. Interaction of confined electrons with bulk acoustic phonons has been considered in the deformation coupling. The study concludes that the dynamically screened deformation potential coupling plays a significant role as it substantially affects the power dependency of electron relaxation on temperature and mean free path.

  9. Spatially indirect excitons in coupled quantum wells

    SciTech Connect

    Lai, Chih-Wei Eddy

    2004-03-01

    Microscopic quantum phenomena such as interference or phase coherence between different quantum states are rarely manifest in macroscopic systems due to a lack of significant correlation between different states. An exciton system is one candidate for observation of possible quantum collective effects. In the dilute limit, excitons in semiconductors behave as bosons and are expected to undergo Bose-Einstein condensation (BEC) at a temperature several orders of magnitude higher than for atomic BEC because of their light mass. Furthermore, well-developed modern semiconductor technologies offer flexible manipulations of an exciton system. Realization of BEC in solid-state systems can thus provide new opportunities for macroscopic quantum coherence research. In semiconductor coupled quantum wells (CQW) under across-well static electric field, excitons exist as separately confined electron-hole pairs. These spatially indirect excitons exhibit a radiative recombination time much longer than their thermal relaxation time a unique feature in direct band gap semiconductor based structures. Their mutual repulsive dipole interaction further stabilizes the exciton system at low temperature and screens in-plane disorder more effectively. All these features make indirect excitons in CQW a promising system to search for quantum collective effects. Properties of indirect excitons in CQW have been analyzed and investigated extensively. The experimental results based on time-integrated or time-resolved spatially-resolved photoluminescence (PL) spectroscopy and imaging are reported in two categories. (i) Generic indirect exciton systems: general properties of indirect excitons such as the dependence of exciton energy and lifetime on electric fields and densities were examined. (ii) Quasi-two-dimensional confined exciton systems: highly statistically degenerate exciton systems containing more than tens of thousands of excitons within areas as small as (10 micrometer){sup 2} were

  10. Quantum state transfer in double-quantum-well devices

    NASA Technical Reports Server (NTRS)

    Jakumeit, Jurgen; Tutt, Marcel; Pavlidis, Dimitris

    1994-01-01

    A Monte Carlo simulation of double-quantum-well (DQW) devices is presented in view of analyzing the quantum state transfer (QST) effect. Different structures, based on the AlGaAs/GaAs system, were simulated at 77 and 300 K and optimized in terms of electron transfer and device speed. The analysis revealed the dominant role of the impurity scattering for the QST. Different approaches were used for the optimization of QST devices and basic physical limitations were found in the electron transfer between the QWs. The maximum transfer of electrons from a high to a low mobility well was at best 20%. Negative differential resistance is hampered by the almost linear rather than threshold dependent relation of electron transfer on electric field. By optimizing the doping profile the operation frequency limit could be extended to 260 GHz.

  11. Electron mobility limited by surface and interface roughness scattering in AlxGa1-xN/GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Wang, Jian-Xia; Yang, Shao-Yan; Wang, Jun; Liu, Gui-Peng; Li, Zhi-Wei; Li, Hui-Jie; Jin, Dong-Dong; Liu, Xiang-Lin; Zhu, Qin-Sheng; Wang, Zhan-Guo

    2013-07-01

    The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.

  12. Electronic quantum confinement in cylindrical potential well

    NASA Astrophysics Data System (ADS)

    Baltenkov, Arkadiy S.; Msezane, Alfred Z.

    2016-04-01

    The effects of quantum confinement on the momentum distribution of electrons confined within a cylindrical potential well have been analyzed. The motivation is to understand specific features of the momentum distribution of electrons when the electron behavior is completely controlled by the parameters of a non-isotropic potential cavity. It is shown that studying the solutions of the wave equation for an electron confined in a cylindrical potential well offers the possibility to analyze the confinement behavior of an electron executing one- or two-dimensional motion in the three-dimensional space within the framework of the same mathematical model. Some low-lying electronic states with different symmetries have been considered and the corresponding wave functions have been calculated; the behavior of their nodes and their peak positions with respect to the parameters of the cylindrical well has been analyzed. Additionally, the momentum distributions of electrons in these states have been calculated. The limiting cases of the ratio of the cylinder length H and its radius R0 have been considered; when the cylinder length H significantly exceeds its radius R0 and when the cylinder radius is much greater than its length. The cylindrical quantum confinement effects on the momentum distribution of electrons in these potential wells have been analyzed. The possible application of the results obtained here for the description of the general features in the behavior of electrons in nanowires with metallic type of conductivity (or nanotubes) and ultrathin epitaxial films (or graphene sheets) are discussed. Possible experiments are suggested where the quantum confinement can be manifested. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.

  13. Terahertz detection using double quantum well devices

    NASA Astrophysics Data System (ADS)

    Khodier, Majid; Christodoulou, Christos G.; Simmons, Jerry A.

    2001-12-01

    This paper discusses the principle of operation of an electrically tunable THz detector, working around 2.54 THz, integrated with a bowtie antenna. The detection is based on the idea of photon-assisted tunneling (PAT) in a double quantum well (DQW) device. The bowtie antenna is used to collect the THz radiation and feed it to the detector for processing. The Bowtie antenna geometry is integrated with the DQW device to achieve broadband characteristic, easy design, and compatibility with the detector fabrication process. The principle of operation of the detector is introduced first. Then, results of different bowtie antenna layouts are presented and discussed.

  14. Quantum Well Infrared Photodetectors (QWIPs) for Astronomy

    NASA Technical Reports Server (NTRS)

    Gunapala, S. D.; Bandara, S. V.; Liu, J. K.; Luong, E.; Bock, J. J.; Ressler, M. E.; Werner, M. W.

    1998-01-01

    In recent years, many research groups in the world have demonstrated large format Quantum Well Infrared Photodetector (QWIP) focal plane arrays for various thermal imaging applications. QWIPs as opposed to conventional low bandgap infrared detectors, are limited by thermionic dark current and not tunneling currents down to 30K or less. As a result the performance of QWIPs can be substantially improved (orders of magnitude) by cooling from 70K to 30K. Cooling does not induce any nonuniformity or 1/f noise in QWIP focal plane arrays. In this paper, we discuss the development of highly uniform long- wavelength QWIPs for astronomical applications.

  15. Corrugated Quantum Well Infrared Photodetectors and Arrays

    NASA Technical Reports Server (NTRS)

    Choi, K. K.; Chen, C. J.; Rohkinson, L. P.; Das, N. C.; Jhabvala, M.

    1999-01-01

    Quantum well infrared photodetectors (QWIPs) have many advantages in infrared detection, mainly due to the mature Ill-V material technology. The employment of the corrugation structure further advances the technology by providing a simple, yet efficient light-coupling scheme. A C-QWIP enjoys the same flexibility as a detector with intrinsic normal incident absorption. In this paper, we will discuss the utilities of C-QWIPs in different applications, including two-color detection and polarization-sensitive detection. Besides practical applications, C-QWIPs are also useful in detector characterization. They can be used for measuring the absorption coefficient of light propagating parallel to the layers under bias and providing information on the energy resolved photoconductive gain. These two quantities have never been measured before. Based on the corrugation design, we have made several modifications that further improve the detector sensitivity without increasing its complexity. Other than the C-QWIP structure, we also continue searching for other sensitive detector architectures. In a quantum grid infrared photodetector, 3-dimensional electron confinement can be achieved, with which the detector is able to absorb light in all directions. At the same time, the photoconductive gain can also be improved. We further improve the design using a blazed structure. All the experimental results are supported by a rigorous electromagnetic modal transmission-line theory developed especially for these types of structures. Preliminary thermal imaging using C-QWIP FPAs validates the advantages of the present approach.

  16. Spin-orbit interaction in multiple quantum wells

    SciTech Connect

    Hao, Ya-Fei

    2015-01-07

    In this paper, we investigate how the structure of multiple quantum wells affects spin-orbit interactions. To increase the interface-related Rashba spin splitting and the strength of the interface-related Rashba spin-orbit interaction, we designed three kinds of multiple quantum wells. We demonstrate that the structure of the multiple quantum wells strongly affected the interface-related Rashba spin-orbit interaction, increasing the interface-related Rashba spin splitting to up to 26% larger in multiple quantum wells than in a stepped quantum well. We also show that the cubic Dresselhaus spin-orbit interaction similarly influenced the spin relaxation time of multiple quantum wells and that of a stepped quantum well. The increase in the interface-related Rashba spin splitting originates from the relationship between interface-related Rashba spin splitting and electron probability density. Our results suggest that multiple quantum wells can be good candidates for spintronic devices.

  17. Conversion of Type of Quantum Well Structure

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng (Inventor)

    2007-01-01

    A method for converting a Type 2 quantum well semiconductor material to a Type 1 material. A second layer of undoped material is placed between first and third layers of selectively doped material, which are separated from the second layer by undoped layers having small widths. Doping profiles are chosen so that a first electrical potential increment across a first layer-second layer interface is equal to a first selected value and/or a second electrical potential increment across a second layer-third layer interface is equal to a second selected value. The semiconductor structure thus produced is useful as a laser material and as an incident light detector material in various wavelength regions, such as a mid-infrared region.

  18. Conversion of type of quantum well structure

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng (Inventor)

    2007-01-01

    A method for converting a Type 2 quantum well semiconductor material to a Type 1 material. A second layer of undoped material is placed between first and third layers of selectively doped material, which are separated from the second layer by undoped layers having small widths. Doping profiles are chosen so that a first electrical potential increment across a first layer-second layer interface is equal to a first selected value and/or a second electrical potential increment across a second layer-third layer interface is equal to a second selected value. The semiconductor structure thus produced is useful as a laser material and as an incident light detector material in various wavelength regions, such as a mid-infrared region.

  19. Nitride based quantum well light-emitting devices having improved current injection efficiency

    DOEpatents

    Tansu, Nelson; Zhao, Hongping; Liu, Guangyu; Arif, Ronald

    2014-12-09

    A III-nitride based device provides improved current injection efficiency by reducing thermionic carrier escape at high current density. The device includes a quantum well active layer and a pair of multi-layer barrier layers arranged symmetrically about the active layer. Each multi-layer barrier layer includes an inner layer abutting the active layer; and an outer layer abutting the inner layer. The inner barrier layer has a bandgap greater than that of the outer barrier layer. Both the inner and the outer barrier layer have bandgaps greater than that of the active layer. InGaN may be employed in the active layer, AlInN, AlInGaN or AlGaN may be employed in the inner barrier layer, and GaN may be employed in the outer barrier layer. Preferably, the inner layer is thin relative to the other layers. In one embodiment the inner barrier and active layers are 15 .ANG. and 24 .ANG. thick, respectively.

  20. Normal incidence intersubband absorption in vertical quantum wells

    NASA Astrophysics Data System (ADS)

    Berger, V.; Vermeire, G.; Demeester, P.; Weisbuch, C.

    1995-01-01

    N-doped vertical AlGaAs quantum wells have been fabricated by metalorganic vapor phase epitaxial growth of a single-doped AlGaAs layer on a submicron grating. Intersubband absorption at normal incidence is demonstrated in those quantum wells. This opens new possibilities for infrared quantum well devices using intersubband transitions.

  1. Multiple functional UV devices based on III-Nitride quantum wells for biological warfare agent detection

    NASA Astrophysics Data System (ADS)

    Wang, Qin; Savage, Susan; Persson, Sirpa; Noharet, Bertrand; Junique, Stéphane; Andersson, Jan Y.; Liuolia, Vytautas; Marcinkevicius, Saulius

    2009-02-01

    We have demonstrated surface normal detecting/filtering/emitting multiple functional ultraviolet (UV) optoelectronic devices based on InGaN/GaN, InGaN/AlGaN and AlxGa1-xN/AlyGa1-yN multiple quantum well (MQW) structures with operation wavelengths ranging from 270 nm to 450 nm. Utilizing MQW structure as device active layer offers a flexibility to tune its long cut-off wavelength in a wide UV range from solar-blind to visible by adjusting the well width, well composition and barrier height. Similarly, its short cut-off wavelength can be adjusted by using a GaN or AlGaN block layer on a sapphire substrate when the device is illuminated from its backside, which further provides an optical filtering effect. When a current injects into the device under forward bias the device acts as an UV light emitter, whereas the device performs as a typical photodetector under reverse biases. With applying an alternating external bias the device might be used as electroabsorption modulator due to quantum confined Stark effect. In present work fabricated devices have been characterized by transmission/absorption spectra, photoresponsivity, electroluminescence, and photoluminescence measurements under various forward and reverse biases. The piezoelectric effect, alloy broadening and Stokes shift between the emission and absorption spectra in different InGaN- and AlGaN-based QW structures have been investigated and compared. Possibilities of monolithic or hybrid integration using such multiple functional devices for biological warfare agents sensing application have also be discussed.

  2. Magnetophonon resonance in double quantum wells

    NASA Astrophysics Data System (ADS)

    Ploch, D.; Sheregii, E. M.; Marchewka, M.; Wozny, M.; Tomaka, G.

    2009-05-01

    The experimental results obtained for the magnetotransport in pulsed magnetic fields in the InGaAs/InAlAs double quantum well (DQW) structures of two different shapes of wells and different values of the electron density are reported. The magnetophonon resonance (MPR) was observed for both types of structures within the temperature range 77-125 K. Four kinds of LO phonons are taken into account to interpret the MPR oscillations in the DQW and a method of the Landau level calculation in the DQW is elaborated for this aim. The peculiarity of the MPR in the DQW is the large number of the Landau levels caused by SAS splitting of the electron states (splitting on the symmetric and anti-symmetric states) and the large number of the phonon assistance electron transitions between Landau levels. The significant role of the carrier statistics is shown too. The behavior of the electron states in the DQWs at comparably high temperatures has been studied using the MPR. It is shown that the Huang and Manasreh [Manasreh [Phys. Rev. B 54, 2044 (1996)] model involving screening of exchange interaction is confirmed.

  3. Angular distribution of polarized light and its effect on light extraction efficiency in AlGaN deep-ultraviolet light-emitting diodes.

    PubMed

    Chen, Xinjuan; Ji, Cheng; Xiang, Yong; Kang, Xiangning; Shen, Bo; Yu, Tongjun

    2016-05-16

    Angular distribution of polarized light and its effect on light extraction efficiency (LEE) in AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) are investigated in this paper. A united picture is presented to describe polarized light's emission and propagation processes. It is found that the electron-hole recombinations in AlGaN multiple quantum wells produce three kinds of angularly distributed polarized emissions and propagation process can change their intensity distributions. By investigation the change of angular distributions in 277nm and 215nm LEDs, this work reveals that LEE can be significantly enhanced by modulating the angular distributions of polarized light of DUV LEDs. PMID:27409966

  4. Quantum well intermixing and radiation effects in InGaN/GaN multi quantum wells

    NASA Astrophysics Data System (ADS)

    Lorenz, K.; Redondo-Cubero, A.; Lourenço, M. B.; Sequeira, M. C.; Peres, M.; Freitas, A.; Alves, L. C.; Alves, E.; Leitão, M. P.; Rodrigues, J.; Ben Sedrine, N.; Correia, M. R.; Monteiro, T.

    2016-02-01

    Compositional grading of InGaN/GaN multi quantum wells (QWs) was proposed to mitigate polarization effects and Auger losses in InGaN-based light emitting diodes [K. P. O'Donnell et al., Phys. Status Solidi RRL 6 (2012) 49]. In this paper we are reviewing our recent attempts on achieving such gradient via quantum well intermixing. Annealing up to 1250 °C resulted in negligible interdiffusion of QWs and barriers revealing a surprising thermal stability well above the typical MOCVD growth temperatures. For annealing at 1400 °C results suggest a decomposition of the QWs in regions with high and low InN content. The defect formation upon nitrogen implantation was studied in detail. Despite strong dynamic annealing effects, which keep structural damage low, the created defects strongly quench the QW luminescence even for low implantation fluences. This degradation could not be reversed during thermal annealing and is hampering the use of implantation induced quantum well intermixing in InGaN/GaN structures.

  5. Enhanced carrier injection in InGaN/GaN multiple quantum wells LED with polarization-induced electron blocking barrier

    NASA Astrophysics Data System (ADS)

    Li, Chengguo; Liu, Hongfei; Chua, Soo Jin

    2016-03-01

    In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In0.1Ga0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al0.2Ga0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.

  6. Magnetic breakdown in double quantum wells

    SciTech Connect

    Harff, N.E. |; Simmons, J.A.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.

    1996-08-01

    The authors find that a sufficiently large perpendicular magnetic field (B{sub {perpendicular}}) causes magnetic breakdown (MB) in coupled double quantum wells (QWs) that are subject to an in-plane magnetic field (B{sub {parallel}}). B{sub {parallel}} shifts one QW dispersion curve with respect to that of the other QW, resulting in an anticrossing and an energy gap. When the gap is below the Fermi level the resulting Fermi surface (FS) consists of two components, a lens-shaped inner orbit and an hour-glass shaped outer orbit. B{sub {perpendicular}} causes Landau level formation and Shubnikov-de Haas (SdH) oscillations for each component of the FS. MB occurs when the magnetic forces from B{sub {perpendicular}} become dominant and the electrons move on free-electron circular orbits rather than on the lens and hour-glass orbits. MB is observed by identifying the peaks present in the Fourier power spectrum of the longitudinal resistance vs. 1/B{sub {perpendicular}} at constant B{sub {parallel}}, an arrangement achieved with an in-situ tilting sample holder. Results are presented for two strongly coupled GaAs/AlGaAs DQW samples.

  7. Ising Quantum Hall Ferromagnetism in AlAs Quantum Wells.

    NASA Astrophysics Data System (ADS)

    de Poortere, Etienne

    2002-03-01

    Though quantum Hall ferromagnetic transitions in two-dimensional (2D) systems are observed in several materials, such transitions in AlAs 2D electrons offer a unique combination of two remarkable properties: (1) the resistance of the carrier system increases sharply at the transition, and (2) these resistance spikes are hysteretic at low temperatures [1]. We have been able to uncover these properties thanks to recent improvements in the quality of our AlAs samples [2], which now attain a mobility as high as 31 m^2/Vs at a density 5 × 10^11 cm-2. These transport phenomena at Ising transitions result in part from the electronic properties of AlAs, which favor a strong competition between exchange, cyclotron and Zeeman energies. Indeed, 2D electrons in AlAs have a high and anisotropic effective band mass comparable to that of Si, and a band g-factor close to 2. In addition, high-density AlAs 2D electrons occupy two X-point valleys of the Brillouin zone, allowing for inter-valley Ising transitions. In this talk we present results from our study of Ising transitions in AlAs 2D electrons. We observe that the hysteretic resistance of a given transition depends sensitively on the occupation of the two levels involved in the transition, increasing in amplitude as these levels are depleted. We also analyze the spike temperature dependence, which shows that unlike the nearby quantum Hall resistance minima, the resistance spikes themselves are not activated. Other parameters are also varied, such as total carrier density and transverse electric field in the AlAs quantum well. A Hartree-Fock picture of these Ising transitions has been drawn, involving magnetic domains and increased scattering at the domain boundaries [3]. Nevertheless, many of the measured dependencies of the Ising transition resistance spikes are not yet qualitatively understood, forming thus a jigsaw puzzle of many parts. [1] E. P. De Poortere et al., Science 290, 1546 (2000). [2] E. P. De Poortere et al

  8. Intersubband absorption properties of high Al content AlxGa1−xN/GaN multiple quantum wells grown with different interlayers by metal organic chemical vapor deposition

    PubMed Central

    2012-01-01

    High Al content AlxGa1−xN/GaN multiple quantum well (MQW) films with different interlayers were grown by metal organic chemical vapor deposition. These MQWs were designed to achieve intersubband (ISB) absorption in the mid-infrared spectral range. We have considered two growth conditions, with AlGaN interlayer and GaN/AlN superlattice (SL) interlayer, both deposited on GaN-on-sapphire templates. Atomic force microscopy images show a relatively rough surface with atomic-step terraces and surface depression, mainly dominated by dislocations. High-resolution X-ray diffraction and transmission electron microscopy analyses indicate that good crystalline quality of the AlGaN/GaN MQW layer could be achieved when the AlGaN interlayer is inserted. The ISB absorption with a peak at 3.7 μm was demonstrated in MQW films with AlGaN interlayer. However, we have not observed the infrared absorption in MQW films with GaN/AlN SL interlayer. It is believed that the high dislocation density and weaker polarization that resulted from the rough interface are determinant factors of vanished ISB absorption for MQW films with the GaN/AlN SL interlayer. PMID:23181766

  9. Material Processing of Quantum Well Infrared Photodetectors

    NASA Astrophysics Data System (ADS)

    Malin, Jay Ira

    1995-01-01

    The material and device characterization of furnace and rapid thermally annealed (RTA) GaAs/AlGaAs multiple quantum well (MQW) infrared (IR) photodetectors (QWIPs) epitaxially grown on GaAs and Si substrates is presented. The advances in epitaxial growth allow the precise control of the dimensions, doping, and matrix concentration of the MQW. Therefore, the design of a QWIP with particular electrical and optical characteristics may be undertaken. To utilize a post-growth anneal to improve the QWIP's performance, the trade-offs must be considered to determine its usefulness. Depending on the application, the anneal may be deemed unnecessary due to its detrimental effect on a particular aspect of the operation. The availability of high quality GaAs and Si substrates, complemented by the maturity of GaAs device processing techniques, makes the QWIP an ideal candidate for 8-14 μm long wavelength infrared (LWIR) detection. An extensive exploration of the interdiffusion process leads to the development of a suitable technique for shifting the optical response without harming the electrical characteristics. This, however, is a difficult task in light of the out-diffusion of the dopant from the wells into the barriers, which results in a high dark current. Reading-out the QWIP focal plane array (FPA) (on GaAs substrate) is accomplished by indium bump-bonding the FPA to a Si multiplexer. Thermal cycling the hybrid, unfortunately, results in destroyed bonds due to the difference in thermal expansion coefficient of the two substrates. Growing the QWIP on a Si substrate better satisfies the packaging requirements; however, the dark current is higher. The technique of annealing for the purpose of defect annihilation results in improvements in the absolute response and a reduction in the dark current.

  10. Transport through quantum wells and superlattices on topological insulator surfaces.

    PubMed

    Song, J-T; Li, Y-X; Sun, Q-F

    2014-05-01

    We investigate electron transmission coefficients through quantum wells and quantum superlattices on topological insulator surfaces. The quantum well or superlattice is not constituted by general electronic potential barriers but by Fermi velocity barriers which originate in the different topological insulator surfaces. It is found that electron resonant modes can be renormalized by quantum wells and more clearly by quantum superlattices. The depth and width of a quantum well and superlattice, the incident angle of an electron, and the Fermi energy can be used to effectively tune the electron resonant modes. In particular, the number N of periodic structures that constitute a superlattice can further strengthen these regulating effects. These results suggest that a device could be developed to select and regulate electron propagation modes on topological insulator surfaces. Finally, we also study the conductance and the Fano factor through quantum wells and quantum superlattices. In contrast to what has been reported before, the suppression factors of 0.4 in the conductance and 0.85 in the Fano factor are observed in a quantum well, while the transport for a quantum superlattice shows strong oscillating behavior at low energy and reaches the same saturated values as in the case of a quantum well at sufficiently large energies.

  11. Single and coupled quantum wells: SiGe

    NASA Astrophysics Data System (ADS)

    Usami, N.; Shiraki, Y.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses single and coupled quantum wells based on SiGe. Topics include the photoluminescence from SiGe/Si quantum wells (spectral features, dependence on excitation power and temperature), effects of quantum confinement, post-growth annealing, electric fields and external stress, the Fermi-edge singularity, time-resolved photoluminescence, growth mode transition, type-II strained Si quantum wells, coupled quantum wells, electroluminescence, interband absorption and intraband absorption, second-harmonic generation, and phonon modes.

  12. Guiding effect of quantum wells in semiconductor lasers

    SciTech Connect

    Aleshkin, V Ya; Dikareva, Natalia V; Dubinov, A A; Zvonkov, B N; Karzanova, Maria V; Kudryavtsev, K E; Nekorkin, S M; Yablonskii, A N

    2013-05-31

    The guiding effect of InGaAs quantum wells in GaAs- and InP-based semiconductor lasers has been studied theoretically and experimentally. The results demonstrate that such waveguides can be effectively used in laser structures with a large refractive index difference between the quantum well material and semiconductor matrix and a large number of quantum wells (e.g. in InP-based structures). (semiconductor lasers. physics and technology)

  13. Energy level spectroscopy of InSb quantum wells using quantum-well LED emission

    NASA Astrophysics Data System (ADS)

    Tenev, T. G.; Palyi, A.; Mirza, B. I.; Nash, G. R.; Fearn, M.; Smith, S. J.; Buckle, L.; Emeny, M. T.; Ashley, T.; Jefferson, J. H.; Lambert, C. J.

    2009-02-01

    We have investigated the low-temperature optical properties of InSb quantum-well (QW) light-emitting diodes, with different barrier compositions, as a function of well width. Three devices were studied: QW1 had a 20 nm undoped InSb quantum well with a barrier composition of Al0.143In0.857Sb , QW2 had a 40 nm undoped InSb well with a barrier composition of Al0.077In0.923Sb , and QW3 had a 100 nm undoped InSb well with a barrier composition of Al0.025In0.975Sb . For QW1, the signature of two transitions (CB1-HH1 and CB1-HH2) can be seen in the measured spectrum, whereas for QW2 and QW3 the signature of a large number of transitions is present in the measured spectra. In particular transitions to HH2 can be seen, the first time this has been observed in AlInSb/InSb heterostructures. To identify the transitions that contribute to the measured spectra, the spectra have been simulated using an eight-band k.p calculation of the band structure together with a first-order time-dependent perturbation method (Fermi golden rule) calculation of spectral emittance, taking into account broadening. In general there is good agreement between the measured and simulated spectra. For QW2 we attribute the main peak in the experimental spectrum to the CB2-HH1 transition, which has the highest overall contribution to the emission spectrum of QW2 compared with all the other interband transitions. This transition normally falls into the category of “forbidden transitions,” and in order to understand this behavior we have investigated the momentum matrix elements, which determine the selection rules of the problem.

  14. Exciton absorption of entangled photons in semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Rodriguez, Ferney; Guzman, David; Salazar, Luis; Quiroga, Luis; Condensed Matter Physics Group Team

    2013-03-01

    The dependence of the excitonic two-photon absorption on the quantum correlations (entanglement) of exciting biphotons by a semiconductor quantum well is studied. We show that entangled photon absorption can display very unusual features depending on space-time-polarization biphoton parameters and absorber density of states for both bound exciton states as well as for unbound electron-hole pairs. We report on the connection between biphoton entanglement, as quantified by the Schmidt number, and absorption by a semiconductor quantum well. Comparison between frequency-anti-correlated, unentangled and frequency-correlated biphoton absorption is addressed. We found that exciton oscillator strengths are highly increased when photons arrive almost simultaneously in an entangled state. Two-photon-absorption becomes a highly sensitive probe of photon quantum correlations when narrow semiconductor quantum wells are used as two-photon absorbers. Research funds from Facultad de Ciencias, Universidad de los Andes

  15. Strain-compensated (Ga,In)N/(Al,Ga)N/GaN multiple quantum wells for improved yellow/amber light emission

    SciTech Connect

    Lekhal, K.; Damilano, B. De Mierry, P.; Vennéguès, P.; Ngo, H. T.; Rosales, D.; Gil, B.; Hussain, S.

    2015-04-06

    Yellow/amber (570–600 nm) emitting In{sub x}Ga{sub 1−x}N/Al{sub y}Ga{sub 1−y}N/GaN multiple quantum wells (QWs) have been grown by metal organic chemical vapor deposition on GaN-on- sapphire templates. When the (Al,Ga)N thickness of the barrier increases, the room temperature photoluminescence is red-shifted while its yield increases. This is attributed to an increase of the QW internal electric field and an improvement of the material quality due to the compensation of the compressive strain of the In{sub x}Ga{sub 1−x}N QWs by the Al{sub y}Ga{sub 1−y}N layers, respectively.

  16. Polaron mass of charge carriers in semiconductor quantum wells

    SciTech Connect

    Maslov, A. Yu. Proshina, O. V.

    2015-10-15

    A theory of the interaction of charge carriers with optical phonons in a quantum well is developed with consideration for interface optical phonons. The dependence of the polaron effective mass on the quantum-well dimensions and dielectric characteristics of barriers is analyzed in detail. It is shown that, in narrow quantum wells, a quasi-two-dimensional polaron can be formed. In this case, however, the interaction parameters are defined by the charge-carrier effective mass in the quantum well and by the frequencies of interface optical phonons. If barriers are made of a nonpolar material, the polaron effective mass depends on the quantum-well width. As the quantum-well width is increased, a new mechanism of enhancement of the electron–phonon interaction develops. The mechanism is implemented, if the optical phonon energy is equal to the energy of one of the electronic transitions. This condition yields an unsteady dependence of the polaron effective mass on the quantum-well width.

  17. Double well potentials and quantum phase transitions in ion traps.

    PubMed

    Retzker, A; Thompson, R C; Segal, D M; Plenio, M B

    2008-12-31

    We demonstrate that the radial degree of freedom of strings of trapped ions in the quantum regime may be prepared and controlled accurately through the variation of the external trapping potential while at the same time its properties are measurable with high spatial and temporal resolution. This provides a new testbed giving access to static and dynamical properties of the physics of quantum-many-body systems and quantum phase transitions that are hard to simulate on classical computers. Furthermore, it allows for the creation of double well potentials with experimentally accessible tunneling rates, with applications in testing the foundations of quantum physics and precision sensing. PMID:19437628

  18. Students' Conceptual Difficulties in Quantum Mechanics: Potential Well Problems

    ERIC Educational Resources Information Center

    Ozcan, Ozgur; Didis, Nilufer; Tasar, Mehmet Fatih

    2009-01-01

    In this study, students' conceptual difficulties about some basic concepts in quantum mechanics like one-dimensional potential well problems and probability density of tunneling particles were identified. For this aim, a multiple choice instrument named Quantum Mechanics Conceptual Test has been developed by one of the researchers of this study…

  19. Single electron tunneling in double and triple quantum wells

    NASA Astrophysics Data System (ADS)

    Filikhin, I.; Karoui, A.; Vlahovic, B.

    2016-03-01

    Electron localization and tunneling in laterally distributed double quantum well (DQW) and triple quantum well (TQW) are studied. Triangular configuration for the TQWs as well as various quantum well (QW) shapes and asymmetry are considered. The effect of adding a third well to a DQW is investigated as a weakly coupled system. InAs/GaAs DQWs and TQWs were modeled using single subband effective mass approach with effective potential simulating the strain effect. Electron localization dynamics in DQW and TQW over the whole spectrum is studied by varying the inter-dot distances. The electron tunneling appeared highly sensitive to small violations of the DQW mirror symmetry. We show that the presence of a third dot increases the tunneling in the DQW. The dependence of the tunneling in quantum dot (QD) arrays on inter-dot distances is also discussed.

  20. Quantum Well Infrared Photodetectors for Low Background Applications

    NASA Technical Reports Server (NTRS)

    Gunapala, S. D.; Bandara, S. V.; Singh, A.; Liu, J. K.; Luong, E. M.; Mumolo, J. M.; McKelvey, M. J.

    1998-01-01

    High performance long-wavelength GaAs/Al(x)Ga(1-x)As quantum well infrared photodetectors for low background applications have been demonstrated. This is the first theoretical analysis of quantum well infrared photodetectors for low background applications and the detectivity D* of 6 x 10(exp 13) cm.square root of Hz/W has been achieved at T = 40 K with 2 x 10(exp 9) photons/cm2/sec background. In addition, this paper describes the demonstration of mid-wavelength/long-wavelength dualband quantum well infrared photodetectors and long-wavelength/very long-wavelength dualband quantum well infrared photodetectors in 4-26 micrometers wavelength region.

  1. Piezo-Phototronic Effect in a Quantum Well Structure.

    PubMed

    Huang, Xin; Du, Chunhua; Zhou, Yongli; Jiang, Chunyan; Pu, Xiong; Liu, Wei; Hu, Weiguo; Chen, Hong; Wang, Zhong Lin

    2016-05-24

    With enhancements in the performance of optoelectronic devices, the field of piezo-phototronics has attracted much attention, and several theoretical works have been reported based on semiclassical models. At present, the feature size of optoelectronic devices are rapidly shrinking toward several tens of nanometers, which results in the quantum confinement effect. Starting from the basic piezoelectricity equation, Schrödinger equation, Poisson equation, and Fermi's golden rule, a self-consistent theoretical model is proposed to study the piezo-phototronic effect in the framework of perturbation theory in quantum mechanics. The validity and universality of this model are well-proven with photoluminescence measurements in a single GaN/InGaN quantum well and multiple GaN/InGaN quantum wells. This study provides important insight into the working principle of nanoscale piezo-phototronic devices as well as guidance for the future device design.

  2. Thermoelectric transport in quantum well superlattices

    SciTech Connect

    Broido, D.A.; Reinecke, T.L.

    1997-05-01

    A full theory of thermoelectric transport in superlattices, including the well width and energy dependence of the optical and acoustic phonon scattering and the effects of confinement in raising valley degeneracy is developed. It is shown that these features result in qualitatively significant modifications in the predicted figure of merit of superlattice systems. Results are given for PbTe superlattices, and comments are made on recent experimental results for such systems. {copyright} {ital 1997 American Institute of Physics.}

  3. Quantum Anomalous Hall Effect in Hg_1-yMn_yTe Quantum Wells

    SciTech Connect

    Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    The quantum Hall effect is usually observed when the two-dimensional electron gas is subjected to an external magnetic field, so that their quantum states form Landau levels. In this work we predict that a new phenomenon, the quantum anomalous Hall effect, can be realized in Hg{sub 1-y}Mn{sub y}Te quantum wells, without the external magnetic field and the associated Landau levels. This effect arises purely from the spin polarization of the Mn atoms, and the quantized Hall conductance is predicted for a range of quantum well thickness and the concentration of the Mn atoms. This effect enables dissipationless charge current in spintronics devices.

  4. Modeling and Simulation of Semiconductor Quantum Well Structures and Lasers

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng; Saini, Subbash (Technical Monitor)

    1998-01-01

    In this talk I will cover two aspects of modeling and simulation efforts at NASA Ames Research Center. In the quantum well structure simulation, we typically start from the quantum mechanical calculation of the quantum well structures for the confined/and unconfined eigen states and functions. A bandstructure calculation of the k*p type is then performed for the confined valence states. This information is then used to computer the optical gain and refractive index of the quantum well structures by solving the linearized multiband semiconductor Bloch equations with the many-body interactions included. In our laser simulation, we typically solve the envelope equations for the laser field in space-time domain, coupled with a reduced set of material equations using the microscopic calculation of the first step. Finally I will show some examples of both aspects of simulation and modeling.

  5. Atmospheric and low pressure metalorganic vapor phase epitaxial growth of vertical quantum wells and quantum well wires on submicron gratings

    NASA Astrophysics Data System (ADS)

    Vermeire, G.; Moerman, I.; Yu, Z. Q.; Vermaerke, F.; van Daele, P.; Demeester, P.

    1994-02-01

    Nonplanar metalorganic vapor phase epitaxial growth on submicron gratings has been studied. Growth conditions have been determined to preserve the grating structure and also to enhance the formation of crescent shaped quantum well wire-like GaAs layers. These growth parameters have been used to grow the layer structure of a quantum well wire (QWW) laser, only needing one growth run. Although there is not yet clear evidence for two-dimensional quantum confinement, this technique offers some interesting perspectives for the realization of QWW lasers.

  6. Luminescence studies on nitride quaternary alloys double quantum wells

    NASA Astrophysics Data System (ADS)

    Rodrigues, S. C. P.; dos Santos, O. F. P.; Scolfaro, L. M. R.; Sipahi, G. M.; da Silva, E. F., Jr.

    2008-09-01

    We present theoretical photoluminescence (PL) spectra of undoped and p-doped Al xIn 1- x- yGa yN/Al XIn 1- X- YGa YN double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange-correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments.

  7. Dot-in-Well Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

  8. Quantum beats in conductance oscillations in graphene-based asymmetric double velocity wells and electrostatic wells

    SciTech Connect

    Liu, Lei; Li, Yu-Xian; Zhang, Ying-Tao; Liu, Jian-Jun

    2014-01-14

    The transport properties in graphene-based asymmetric double velocity well (Fermi velocity inside the well less than that outside the well) and electrostatic well structures are investigated using the transfer matrix method. The results show that quantum beats occur in the oscillations of the conductance for asymmetric double velocity wells. The beating effect can also be found in asymmetric double electrostatic wells, but only if the widths of the two wells are different. The beat frequency for the asymmetric double well is exactly equal to the frequency difference between the oscillation rates in two isolated single wells with the same structures as the individual wells in the double well structure. A qualitative interpretation is proposed based on the fact that the resonant levels depend upon the sizes of the quantum wells. The beating behavior can provide a new way to identify the symmetry of double well structures.

  9. Semiconductor quantum wells: old technology or new device functionalities

    NASA Astrophysics Data System (ADS)

    Kolbas, R. M.; Lo, Y. C.; Hsieh, K. Y.; Lee, J. H.; Reed, F. E.; Zhang, D.; Zhang, T.

    2009-08-01

    The introduction of semiconductor quantum wells in the 1970s created a revolution in optoelectronic devices. A large fraction of today's lasers and light emitting diodes are based on quantum wells. It has been more than 30 years but novel ideas and new device functions have recently been demonstrated using quantum well heterostructures. This paper provides a brief overview of the subject and then focuses on the physics of quantum wells that the lead author believes holds the key to new device functionalities. The data and figures contained within are not new. They have been assembled from 30 years of work. They are presented to convey the story of why quantum wells continue to fuel the engine that drives the semiconductor optoelectronic business. My apologies in advance to my students and co-workers that contributed so much that could not be covered in such a short manuscript. The explanations provided are based on the simplest models possible rather than the very sophisticated mathematical models that have evolved over many years. The intended readers are those involved with semiconductor optoelectronic devices and are interested in new device possibilities.

  10. Spatial light modulators with arbitrary quantum well profiles

    NASA Astrophysics Data System (ADS)

    Marcas, George N.; Bajaj, Krishan K.

    1992-02-01

    This is the 2nd year technical report for the University Research Initiative (URI) Program, Spatial Light Modulators with Arbitrary Quantum Well Profiles. During the second year of the program, we have continued to optimize optical modulator design, growth, and fabrication. A new method for self-consistent solution of Schroedinger and Poisson equations was developed and used to predict modulator active region performance and vertical cavity surface emitting laser device performance. A comprehensive comparison of asymmetric triangular quantum wells (ATQW) using GaAs/AlGaAs, InGaAs/GaAs, and InGaAs/AlGaAs showed InGaAs/AlGaAs quantum wells to have the highest optical efficiency. A MBE compositional grading technique was used to achieve record narrow photoluminescence linewidths for nonrectangular quantum wells. Bragg reflectors for use in Fabry Perot modulators were measured in-situ by spectroscopic ellipsometry (SE). Advances were made in the growth and fabrication of p-i-n optical modulators, including the development of via hole etching through the substrate for transmission mode modulators. A simple variational method for calculating excitonic properties in quantum confined structures with arbitrary potential profiles in the presence of applied electric and magnetic fields were developed and applied to the study of energy levels of hydrogenic impurities. Also, a theory of radiative transition linewidths due to alloy disordering in semiconductor alloys has been presented and applied to AlGaAs and InGaP bulk alloys.

  11. [The photoluminescence characteristics of organic multilayer quantum wells].

    PubMed

    Zhao, De-Wei; Song, Shu-Fang; Zhao, Su-Ling; Xu, Zheng; Wang, Yong-Sheng; Xu, Xu-Rong

    2007-04-01

    By the use of multi-source high-vaccum organic beam deposition system, the authors prepared organic multilayer quantum well structures, which consist of alternate organic small molecule materials PBD and Alq3. Based on 4-period organic quantum wells, different samples with different thickness barriers and wells were prepared. The authors measured the lowest unoccupied molecular orbit (LUMO) and the highest occupied molecular orbit (HOMO) by electrochemistry cyclic voltammetry and optical absorption. From the energy diagrams, it seems like type-I quantum well structures of the inorganic semiconductor, in which PBD is used as a barrier layer and Alq3 as a well layer and emitter. From small angle X-ray diffraction measurements, the results indicate that these structures have high interface quality and uniformity. The photoluminescence characteristics of organic multilayer quantum wells were investigated. The PL peak has a blue-shift with the decrease of the well layer thickness. Meanwhile as the barrier thickness decreases the PL peaks of PBD disappear gradually. And the energy may be effectively transferred from PBD to Alq3, inducing an enhancement of the luminescence of Alq3.

  12. Spin current injection by intersubband transitions in quantum wells.

    NASA Astrophysics Data System (ADS)

    Sherman, Eugene

    2005-03-01

    We show that a pure spin current can be injected in quantum wells by absorption of linearly polarized infrared radiation leading to transitions between subbands. The magnitude and the direction of the spin current depend on the Dresselhaus and Rashba spin-orbit coupling constants and light frequency and, therefore, can be manipulated by changing the light frequency and/or applying an external bias across the quantum well. The injected spin current should be observable either as a voltage generated via extrinsic spin-Hall effect, or by spatially resolved pump-probe optical spectroscopy.

  13. Microscopic Theory and Simulation of Quantum-Well Intersubband Absorption

    NASA Technical Reports Server (NTRS)

    Li, Jianzhong; Ning, C. Z.

    2004-01-01

    We study the linear intersubband absorption spectra of a 15 nm InAs quantum well using the intersubband semiconductor Bloch equations with a three-subband model and a constant dephasing rate. We demonstrate the evolution of intersubband absorption spectral line shape as a function of temperature and electron density. Through a detailed examination of various contributions, such as the phase space filling effects, the Coulomb many-body effects and the non-parabolicity effect, we illuminate the underlying physics that shapes the spectra. Keywords: Intersubband transition, linear absorption, semiconductor heterostructure, InAs quantum well

  14. Detection of electromagnetic radiation using micromechanical multiple quantum wells structures

    DOEpatents

    Datskos, Panagiotis G [Knoxville, TN; Rajic, Slobodan [Knoxville, TN; Datskou, Irene [Knoxville, TN

    2007-07-17

    An apparatus and method for detecting electromagnetic radiation employs a deflectable micromechanical apparatus incorporating multiple quantum wells structures. When photons strike the quantum-well structure, physical stresses are created within the sensor, similar to a "bimetallic effect." The stresses cause the sensor to bend. The extent of deflection of the sensor can be measured through any of a variety of conventional means to provide a measurement of the photons striking the sensor. A large number of such sensors can be arranged in a two-dimensional array to provide imaging capability.

  15. Optical properties of transition metal oxide quantum wells

    SciTech Connect

    Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

    2015-01-21

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO{sub 3}/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  16. AlSb/InAs/AlSb quantum wells

    NASA Technical Reports Server (NTRS)

    Kroemer, Herbert

    1990-01-01

    Researchers studied the InAs/AlSb system recently, obtaining 12nm wide quantum wells with room temperature mobilities up to 28,000 cm(exp 2)/V center dot S and low-temperature mobilities up to 325,000 cm(exp 2)/V center dot S, both at high electron sheet concentrations in the 10(exp 12)/cm(exp 2) range (corresponding to volume concentrations in the 10(exp 18)/cm(exp 2) range). These wells were not intentionally doped; the combination of high carrier concentrations and high mobilities suggest that the electrons are due to not-intentional modulation doping by an unknown donor in the AlSb barriers, presumably a stoichiometric defect, like an antisite donor. Inasmuch as not intentionally doped bulk AlSb is semi-insulating, the donor must be a deep one, being ionized only by draining into the even deeper InAs quantum well. The excellent transport properties are confirmed by other observations, like excellent quantum Hall effect data, and the successful use of the quantum wells as superconductive weak links between Nb electrodes, with unprecendentedly high critical current densities. The system is promising for future field effect transistors (FETs), but many processing problems must first be solved. Although the researchers have achieved FETs, the results so far have not been competitive with GaAs FETs.

  17. Stimulated emission and optical gain in AlGaN heterostructures grown on bulk AlN substrates

    SciTech Connect

    Guo, Wei Bryan, Zachary; Kirste, Ronny; Bryan, Isaac; Hussey, Lindsay; Bobea, Milena; Haidet, Brian; Collazo, Ramón; Sitar, Zlatko; Xie, Jinqiao; Mita, Seiji; Gerhold, Michael

    2014-03-14

    Optical gain spectra for ∼250 nm stimulated emission were compared in three different AlGaN-based structures grown on single crystalline AlN substrates: a single AlGaN film, a double heterostructure (DH), and a Multiple Quantum Well (MQW) structure; respective threshold pumping power densities of 700, 250, and 150 kW/cm{sup 2} were observed. Above threshold, the emission was transverse-electric polarized and as narrow as 1.8 nm without a cavity. The DH and MQW structures showed gain values of 50–60 cm{sup −1} when pumped at 1 MW/cm{sup 2}. The results demonstrated the excellent optical quality of the AlGaN-based heterostructures grown on AlN substrates and their potential for realizing electrically pumped sub-280 nm laser diodes.

  18. Generation of infrared entangled light in asymmetric semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Lü, Xin-You; Wu, Jing; Zheng, Li-Li; Huang, Pei

    2010-12-01

    We proposed a scheme to achieve two-mode CV entanglement with the frequencies of entangled modes in the infrared range in an asymmetric semiconductor double-quantum-wells (DQW), where the required quantum coherence is obtained by inducing the corresponding intersubband transitions (ISBTs) with a classical field. By numerically simulating the dynamics of system, we show that the entanglement period can be prolonged via enhancing the intensity of classical field, and the generation of entanglement doesn't depend intensively on the initial condition of system in our scheme. Moreover, we also show that a bipartite entanglement amplifier can be realized in our scheme. The present research provides an efficient approach to achieve infrared entangled light in the semiconductor nanostructure, which may have significant impact on the progress of solid-state quantum information theory.

  19. Electron transport in coupled double quantum wells and wires

    SciTech Connect

    Harff, N.E.; Simmons, J.A.; Lyo, S.K.

    1997-04-01

    Due to inter-quantum well tunneling, coupled double quantum wells (DQWs) contain an extra degree of electronic freedom in the growth direction, giving rise to new transport phenomena not found in single electron layers. This report describes work done on coupled DQWs subject to inplane magnetic fields B{sub {parallel}}, and is based on the lead author`s doctoral thesis, successfully defended at Oregon State University on March 4, 1997. First, the conductance of closely coupled DQWs in B{sub {parallel}} is studied. B{sub {parallel}}-induced distortions in the dispersion, the density of states, and the Fermi surface are described both theoretically and experimentally, with particular attention paid to the dispersion anticrossing and resulting partial energy gap. Measurements of giant distortions in the effective mass are found to agree with theoretical calculations. Second, the Landau level spectra of coupled DQWs in tilted magnetic fields is studied. The magnetoresistance oscillations show complex beating as Landau levels from the two Fermi surface components cross the Fermi level. A third set of oscillations resulting from magnetic breakdown is observed. A semiclassical calculation of the Landau level spectra is then performed, and shown to agree exceptionally well with the data. Finally, quantum wires and quantum point contacts formed in DQW structures are investigated. Anticrossings of the one-dimensional DQW dispersion curves are predicted to have interesting transport effects in these devices. Difficulties in sample fabrication have to date prevented experimental verification. However, recently developed techniques to overcome these difficulties are described.

  20. Quantum spin hall insulator state in HgTe quantum wells.

    PubMed

    König, Markus; Wiedmann, Steffen; Brüne, Christoph; Roth, Andreas; Buhmann, Hartmut; Molenkamp, Laurens W; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2007-11-01

    Recent theory predicted that the quantum spin Hall effect, a fundamentally new quantum state of matter that exists at zero external magnetic field, may be realized in HgTe/(Hg,Cd)Te quantum wells. We fabricated such sample structures with low density and high mobility in which we could tune, through an external gate voltage, the carrier conduction from n-type to p-type, passing through an insulating regime. For thin quantum wells with well width d < 6.3 nanometers, the insulating regime showed the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d > 6.3 nanometers), the nominally insulating regime showed a plateau of residual conductance close to 2e(2)/h, where e is the electron charge and h is Planck's constant. The residual conductance was independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance was destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d = 6.3 nanometers, was also independently determined from the magnetic field-induced insulator-to-metal transition. These observations provide experimental evidence of the quantum spin Hall effect.

  1. Cathodoluminescence of single quantum wires and vertical quantum wells grown on a submicron grating

    NASA Astrophysics Data System (ADS)

    Gustafsson, A.; Samuelson, L.; Malm, J.-O.; Vermeire, G.; Demeester, P.

    1994-02-01

    We present cathodoluminescence (CL) investigations of a corrugated GaAs/AlGaAs single quantum well (QW) structure grown on a submicron grating. The CL spectra have four distinct emission peaks. Using plan-view and cross-sectional CL imaging together with cross-sectional transmission electron microscope imaging, we have assigned the four peaks: They originate in the nominal QW, a quantum wire (QWR), a vertical quantum well (VQW), and the barrier, respectively. We have CL-imaged and -characterized single QWRs and VQWs.

  2. Unusual Tunneling Characteristics of Double-quantum-well Heterostructures

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Nitta, J.; Newaz, A. K. M.; Song, W.; Mendez, E. E.

    2005-06-01

    We report tunneling phenomena in double In0.53Ga0.47As quantum-well structures that are at odds with the conventional parallel-momentum-conserving picture of tunneling between two-dimensional systems. We found that the tunneling current was mostly determined by the correlation between the emitter and the state in one well, and not by that between those in both wells. Clear magnetic-field-dependent features were first observed before the main resonance, corresponding to tunneling channels into the Landau levels of the well near the emitter. These facts provide evidence of the violation of in-plane momentum conservation in two-dimensional systems.

  3. Quantum cascade light emitting diodes based on type-2 quantum wells

    NASA Technical Reports Server (NTRS)

    Lin, C. H.; Yang, R. Q.; Zhang, D.; Murry, S. J.; Pei, S. S.; Allerman, A. A.; Kurtz, S. R.

    1997-01-01

    The authors have demonstrated room-temperature CW operation of type-2 quantum cascade (QC) light emitting diodes at 4.2 (micro)m using InAs/InGaSb/InAlSb type-2 quantum wells. The type-2 QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-2 quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 (micro)W at 80 K, and 140 (micro)W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

  4. Quantum cascade light emitting diodes based on type-II quantum wells

    SciTech Connect

    Lin, C.H.; Yang, R.Q.; Zhang, D.; Murry, S.J.; Pei, S.S.; Allerman, A.A.; Kurtz, S.R.

    1997-01-21

    The authors have demonstrated room-temperature CW operation of type-II quantum cascade (QC) light emitting diodes at 4.2 {micro}m using InAs/InGaSb/InAlSb type-II quantum wells. The type-II QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-II quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 {micro}W at 80 K, and 140 {micro}W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

  5. High signal-to-noise ratio quantum well bolometer materials

    NASA Astrophysics Data System (ADS)

    Wissmar, Stanley; Höglund, Linda; Andersson, Jan; Vieider, Christian; Savage, Susan; Ericsson, Per

    2006-09-01

    Novel single crystalline high-performance temperature sensing materials (quantum well structures) have been developed for the manufacturing of uncooled infrared bolometers. SiGe/Si and AlGaAs/GaAs quantum wells are grown epitaxially on standard Si and GaAs substrates respectively. The former use holes as charge carriers utilizing the discontinuities in the valence band structure, whereas the latter operate in a similar manner with electrons in the conduction band. By optimizing parameters such as the barrier height (by variation of the germanium/aluminium content respectively) and the fermi level E f (by variation of the quantum well width and doping level) these materials provide the potential to engineer layer structures with a very high temperature coefficient of resistance, TCR, as compared with conventional thin film materials such as vanadium oxide and amorphous silicon. In addition, the high quality crystalline material promises very low 1/f-noise characteristics promoting an outstanding signal to noise ratio and well defined and uniform material properties, A comparison between the two (SiGe/Si and AlGaAs/GaAs) quantum well structures and their fundamental theoretical limits are discussed and compared to experimental results. A TCR of 2.0%/K and 4.5%/K have been obtained experimentally for SiGe/Si and AlGaAs/GaAs respectively. The noise level for both materials is measured as being several orders of magnitude lower than that of a-Si and VOx. These uncooled thermistor materials can be hybridized with read out circuits by using conventional flip-chip assembly or wafer level adhesion bonding. The increased bolometer performance so obtained can either be exploited for increasing the imaging system performance, i. e. obtaining a low NETD, or to reduce the vacuum packaging requirements for low cost applications (e.g. automotive).

  6. Ferroelectric tunnel junctions with multi-quantum well structures

    SciTech Connect

    Ma, Zhijun; Zhang, Tianjin; Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan

    2014-06-02

    Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.

  7. Intersubband Transitions in InAs/AlSb Quantum Wells

    NASA Technical Reports Server (NTRS)

    Li, J.; Koloklov, K.; Ning, C. Z.; Larraber, D. C.; Khodaparast, G. A.; Kono, J.; Ueda, K.; Nakajima, Y.; Sasa, S.; Inoue, M.

    2003-01-01

    We have studied intersubband transitions in InAs/AlSb quantum wells experimentally and theoretically. Experimentally, we performed polarization-resolved infrared absorption spectroscopy to measure intersubband absorption peak frequencies and linewidths as functions of temperature (from 4 K to room temperature) and quantum well width (from a few nm to 10 nm). To understand experimental results, we performed a self-consistent 8-band k-p band-structure calculation including spatial charge separation. Based on the calculated band structure, we developed a set of density matrix equations to compute TE and TM optical transitions self-consistently, including both interband and intersubband channels. This density matrix formalism is also ideal for the inclusion of various many-body effects, which are known to be important for intersubband transitions. Detailed comparison between experimental data and theoretical simulations is presented.

  8. Proximity Effects in Nb/InAs Quantum Well Structures

    NASA Astrophysics Data System (ADS)

    Eckhause, T. A.; Gwinn, E. G.; Thomas, M.; Kroemer, H.

    1997-03-01

    InAs has been widely used as a weak link in superconductor-semiconductor-superconductor junctions.(E. L. Yuh et al., Surf. Sci. 361/362), 315 (1996) Most theoretical treatments of such structures assume that proximity to InAs does not reduce the Nb gap. To test this assumption we have fabricated structures with an ultra-thin layer of Nb on the exposed surface of the InAs quantum well. After removing the cap layer from the μ = 210,000 cm/V\\cdot s, ns = 5.5 x 10^12cm-2 InAs quantum well, Nb films of ~ 100Åthickness are deposited simultaneously on the 150Åquantum well and on a semi-insulating GaAs substrate (both surfaces are sputter cleaned prior to deposition). We cap the Nb with a ~100ÅSi layer of to prevent oxidation.(S.I. Park and T.H. Geballe, Physica B 135), 108 (1985) After processing, the sheet resistances just above Tc are 23.5Ω and 67Ω in the Nb film and quantum well, respectively. We observed a ~ 0.2K lower critical temperature in the Nb/InAs sample. As the Nb films are otherwise nominally identical and the proximity effect is known to suppress the critical temperature of thin films, this suppression in Tc may be due to the reduction of the gap in Nb. Supported by NSF grant DMR-93-14899

  9. Noise gain and operating temperature of quantum well infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Liu, H. C.

    1992-11-01

    The difference between the noise gain associated with dark current and the photoconductive gain in quantum well infrared photodetectors is discussed in light of recent experiments. The theoretical model is based on a single key parameter: the electron trapping probability. An empirical expression for the trapping probability or, alternatively, the electron escape probability is proposed. Using the dark current, the gain, the trapping probability expressions, and the device operating temperature for achieving background limited infrared performance is discussed.

  10. Temperature independent quantum well FET with delta channel doping

    NASA Technical Reports Server (NTRS)

    Young, P. G.; Mena, R. A.; Alterovitz, S. A.; Schacham, S. E.; Haugland, E. J.

    1992-01-01

    A temperature independent device is presented which uses a quantum well structure and delta doping within the channel. The device requires a high delta doping concentration within the channel to achieve a constant Hall mobility and carrier concentration across the temperature range 300-1.4 K. Transistors were RF tested using on-wafer probing and a constant G sub max and F sub max were measured over the temperature range 300-70 K.

  11. Quantum-well diode frequency multipliers - Varistor case

    NASA Technical Reports Server (NTRS)

    Batelaan, Paul D.; Tolmunen, Timo J.; Frerking, Margaret A.

    1992-01-01

    Local oscillators for heterodyne receivers at submillimeter wavelengths are typically made using a fundamental source followed by a harmonic frequency multiplier. An investigation of the required circuit embedding conditions for a possible new harmonic generator, the quantum-well resonant-tunneling diode, is summarized. A low-frequency multiplier has been tested that employs the resistive nonlinearity of the device as opposed to the reactive nonlinearity. The results show good agreement between practice and theory.

  12. Terahertz quantum well photodetectors with reflection-grating couplers

    SciTech Connect

    Zhang, R.; Fu, Z. L.; Gu, L. L.; Guo, X. G.; Cao, J. C.

    2014-12-08

    The design, fabrication, and characterization of terahertz (THz) quantum well photodetectors with one-dimensional reflection-grating coupler are presented. It is found that the reflection gratings could effectively couple the THz waves normally incident to the device. Compared with the 45-degree facet sample, the peak responsivity of this grating-coupled detector is enhanced by over 20%. The effects of the gratings on the photocurrent spectra are also analyzed.

  13. A Voltage-Tunable Quantum Well Detector for Terahertz Radiation

    NASA Astrophysics Data System (ADS)

    Briceño, G.; Williams, J. B.; Sherwin, M. S.; Campman, K.; Gossard, A. C.

    1997-03-01

    Intersubband transitions in quantum wells have enabled the development of sensitive quantum well infrared photoconductors (QWIP) at wavelengths shorter than 20 microns. The potential of quantum well-based detectors at wavelengths of order 100 microns (3 Terahertz (THz)) has not been realized. We propose a novel antenna-coupled intersubband detector for THz frequencies. The detector is predicted to be sensitive only in a narrow band of frequencies which can be tuned by a factor of order two by applying dc voltages of order 1V. The speed of the detector is predicted to be limited by the intersubband relaxation rate (1 ns at T=10K)(J. N. Heyman et. al., Phys. Rev. Lett. 74), 2682 (1995). Prototype detectors have been constructed. The structure, dc transport characteristics and response of these devices to THz radiation will be discussed. Supported by the NSF Science and Technology Center for Quantized Electronic Structures DMR 91-20007, NSF DMR 9623874, AFOSR F-49620-94-1-0158, and the Ford Foundation (GB).

  14. Quantum Well and Quantum Dot Modeling for Advanced Infrared Detectors and Focal Plane Arrays

    NASA Technical Reports Server (NTRS)

    Ting, David; Gunapala, S. D.; Bandara, S. V.; Hill, C. J.

    2006-01-01

    This viewgraph presentation reviews the modeling of Quantum Well Infrared Detectors (QWIP) and Quantum Dot Infrared Detectors (QDIP) in the development of Focal Plane Arrays (FPA). The QWIP Detector being developed is a dual band detector. It is capable of running on two bands Long-Wave Infrared (LWIR) and Medium Wavelength Infrared (MWIR). The same large-format dual-band FPA technology can be applied to Quantum Dot Infrared Photodetector (QDIP) with no modification, once QDIP exceeds QWIP in single device performance. Details of the devices are reviewed.

  15. Interplay between Coulomb interaction and quantum interference in three-level resonant asymmetric double quantum wells

    SciTech Connect

    Alsing, P. M.; Huang, D. H.; Cardimona, D. A.; Apostolova, T.

    2003-09-01

    A many-body density-matrix theory is derived by including quasiparticle renormalization of kinetic energy and dipole coupling to an external electromagnetic field, as well as the screening and quantum-interference effects. This theory is applied to a three-level resonant asymmetric double-quantum-well system in which the ground subband is coupled to the upper tunneling-split doublet by a strong external electromagnetic field. By using this theory, the quasiparticle energy-level separations and off-diagonal radiative-decay coupling rates, absorption coefficient, refractive-index function, and scaled subband electron density are calculated as functions of incident photon energy. The effects of quasiparticle renormalization on the quantum interference between a pair of optically induced polarizations are analyzed. The quantum interference is shown to be robust against the Coulomb-interaction effect in the mean-field approximation. The roles played by the dephasing rate and electron density are explained.

  16. Magneto-optical properties of indium antimide based quantum wells

    NASA Astrophysics Data System (ADS)

    Khodaparast, Giti Adham

    2001-08-01

    The goal of this work was to study the band structure and spin properties of the InSb quantum wells experimentally. Many new observations resulted such as spin resolved cyclotron resonance and zero field spin splitting in InSb quantum wells. Our cyclotron resonance experimental results are in good agreement with our theoretical model. The values of the effective mass show the expected nonparabolicity behavior. We observed spin resolved cyclotron resonance in the high mobility samples with a rather unexpected amplitude pattern at 70.6 μm which might be a result of deviation from the Kohn theorem. More experiments using FTIR are required to understand the spin resolved cyclotron resonance in InSb. We observe electron spin resonance using FIR laser spectroscopy in symmetric and asymmetric InSb quantum wells over a wide range of magnetic field and the Landau level index. The behavior of the asymmetric wells at low magnetic fields with g-factors far in excess of the bulk g-factor of InSb is due to spin splitting at zero magnetic field. Asymmetry-induced shifts in the spin resonance at high fields depend on the Landau level index as predicted by the Bychkov-Rashba model. In an extension of this work, we plan to compare samples where the asymmetry in the confinement potential is due to differing Al concentrations in the barriers on either side of the quantum well to samples with asymmetric doping which were studied in this work. The α values measured in this work (1.5 × 10-9 eVcm) are among the largest reported as would be expected for a material like InSb with a large bulk g-factor. Recently, in gated InAs samples [61] α values ranging from 2 × 10-9 to 4 × 10-9 eV cm have been measured which suggest that we can achieve even larger α in InSb quantum wells. We are extending our spin resonance studies to gated samples. These should give us the ability to study the spin resonance in the absence of any applied magnetic field.

  17. Radiation Hard AlGaN Detectors and Imager

    SciTech Connect

    2012-05-01

    Radiation hardness of AlGaN photodiodes was tested using a 65 MeV proton beam with a total proton fluence of 3x10{sup 12} protons/cm{sup 2}. AlGaN Deep UV Photodiode have extremely high radiation hardness. These new devices have mission critical applications in high energy density physics (HEDP) and space explorations. These new devices satisfy radiation hardness requirements by NIF. NSTec is developing next generation AlGaN optoelectronics and imagers.

  18. Formation of a self-consistent double quantum well in a wide p-type quantum well

    NASA Astrophysics Data System (ADS)

    Alshanskiǐ, G. A.; Yakunin, M. V.

    2004-11-01

    The process of formation of self-consistent double quantum wells (DQWs) in a wide p-type quantum well in the presence of uniaxial strain is investigated. A feature of p-type systems is the structure of the valence band, which consists of two branches of energy dispersion—light and heavy holes. It is shown that this feature leads to significant splitting of the subbands of symmetric and antisymmetric states, as a result of which it is difficult to form states of the DQW with a vanishingly small tunneling gap; a uniaxial strain, by lifting the degeneracy of the band, suppresses this property, so that the two ground subbands of the size quantization of the DQW remain degenerate to high energies.

  19. Metallic behaviour in SOI quantum wells with strong intervalley scattering.

    PubMed

    Renard, V T; Duchemin, I; Niida, Y; Fujiwara, A; Hirayama, Y; Takashina, K

    2013-01-01

    The fundamental properties of valleys are recently attracting growing attention due to electrons in new and topical materials possessing this degree-of-freedom and recent proposals for valleytronics devices. In silicon MOSFETs, the interest has a longer history since the valley degree of freedom had been identified as a key parameter in the observation of the controversial "metallic behaviour" in two dimensions. However, while it has been recently demonstrated that lifting valley degeneracy can destroy the metallic behaviour, little is known about the role of intervalley scattering. Here, we show that the metallic behaviour can be observed in the presence of strong intervalley scattering in silicon on insulator (SOI) quantum wells. Analysis of the conductivity in terms of quantum corrections reveals that interactions are much stronger in SOI than in conventional MOSFETs, leading to the metallic behaviour despite the strong intervalley scattering. PMID:23774638

  20. Electrostatic enhancement of light emitted by semiconductor quantum well

    NASA Astrophysics Data System (ADS)

    Krokhin, A.; Neogi, A.; Llopis, A.; Mahat, M.; Gumen, L.; Pereira, S.; Watson, I.

    2015-10-01

    Carrier dynamics in metal-semiconductor structures is driven by electrodynamic coupling of carriers to the evanescent field of surface plasmons. Useful modifications in electron and hole dynamics due to presence of metallic inclusions show promise for applications from light emitters to communications. However, this picture does not include contributions from electrostatics. We propose here an electrostatic mechanism for enhancement of light radiated from semiconductor emitter which is comparable in effect to plasmonic mechanism. Arising from Coulomb attraction of e-h pairs to their electrostatic images in metallic nanoparticles, this mechanism produces large carrier concentrations near the nanoparticle. A strong inhomogeneity in the carrier distribution and an increase in the internal quantum efficiency are predicted. In our experiments, this manifests as emission enhancement in InGaN quantum well (QW) radiating in the near-UV region. This fundamental mechanism provides a new perspective for improving the efficiency of broadband light emitters.

  1. Metallic behaviour in SOI quantum wells with strong intervalley scattering.

    PubMed

    Renard, V T; Duchemin, I; Niida, Y; Fujiwara, A; Hirayama, Y; Takashina, K

    2013-01-01

    The fundamental properties of valleys are recently attracting growing attention due to electrons in new and topical materials possessing this degree-of-freedom and recent proposals for valleytronics devices. In silicon MOSFETs, the interest has a longer history since the valley degree of freedom had been identified as a key parameter in the observation of the controversial "metallic behaviour" in two dimensions. However, while it has been recently demonstrated that lifting valley degeneracy can destroy the metallic behaviour, little is known about the role of intervalley scattering. Here, we show that the metallic behaviour can be observed in the presence of strong intervalley scattering in silicon on insulator (SOI) quantum wells. Analysis of the conductivity in terms of quantum corrections reveals that interactions are much stronger in SOI than in conventional MOSFETs, leading to the metallic behaviour despite the strong intervalley scattering.

  2. Recent Developments in Quantum-Well Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, S. D.; Bandara, K. M. S. V.

    1995-01-01

    Intrinsic infrared (IR) detectors in the long wavelength range (8-20 Am) are based on an optically excited interband transition, which promotes an electron across the band gap (E(sub g)) from the valence band to the conduction band as shown. These photoelectrons can be collected efficiently, thereby producing a photocurrent in the external circuit. Since the incoming photon has to promote an electron from the valence band to the conduction band, the energy of the photon (h(sub upsilon)) must be higher than the E(sub g) of the photosensitive material. Therefore, the spectral response of the detectors can be controlled by controlling the E(sub g) of the photosensitive material. Examples for such materials are Hg(1-x), Cd(x), Te, and Pb(1-x), Sn(x), Te, in which the energy gap can be controlled by varying x. This means detection of very-long-wavelength IR radiation up to 20 microns requires small band gaps down to 62 meV. It is well known that these low band gap materials, characterized by weak bonding and low melting points, are more difficult to grow and process than large-band gap semiconductors such as GaAs. These difficulties motivate the exploration of utilizing the intersub-band transitions in multiquantum well (MQW) structures made of more refractory large-band gap semiconductors. The idea of using MQW structures to detect IR radiation can be explained by using the basic principles of quantum mechanics. The quantum well is equivalent to the well-known particle in a box problem in quantum mechanics, which can be solved by the time independent Schroudiner equation.

  3. Theoretical Studies of the Optoelectronic Properties of Semiconductor Quantum Wells.

    NASA Astrophysics Data System (ADS)

    Chao, Calvin Yi-Ping

    The valence-band structure of a semiconductor quantum well is calculated based on the multiband effective -mass theory. A unitary transformation is found to diagonalize the six-by-six Luttinger-Kohn Hamiltonian into two three -by-three blocks, making the computation more efficient. With this new formulation, the effect of strain on the band structure is studied systematically for both the compressional and tensile strain. The importance of the coupling between the heavy-hole, light-hole bands and the spin-orbit split -off bands is especially pointed out. The resonant tunneling of holes through a double -barrier structure is investigated using a transfer-matrix technique. It is shown that the strong mixing between the heavy holes and the light holes results in a totally different I-V characteristic from that predicted previously by the parabolic-band model. The exciton equation in momentum space is solved by using a modified Gaussian quadrature method. The exact solutions for a pure-two-dimensional exciton are derived by means of the Mehler-Fock transform, and the accuracy of the quadrature method is checked by comparing the numerical solutions against the exact solutions. A complete theory for quantum-well excitons is developed taking into account the effects of the valence -band mixing and the intersubband Coulomb interaction. Optical absorption spectra are calculated and compared to experimental data. The comparison demonstrates that the theory explains very well the quantum-confined Stark effect, the polarization selection rule, the coupling between the interwell and intrawell excitons in a multiwell structure, and the anticrossing between the ground state of a light-hole exciton and the excited state of a heavy-hole exciton observed experimentally.

  4. Electron relaxation in quantum dot and quantum well systems by the ICD mechanism

    NASA Astrophysics Data System (ADS)

    Moiseyev, Nimrod

    2014-05-01

    Electron relaxation in quantum dot (QD) and quantum well (QW) systems has a significant impact on QD and QW optoelectronic devices such as lasers, photodetectors, and solar cells. Several different fundamental relaxation mechanisms are known. We focus here on inter-coulombic decay (ICD) mechanism. In 2011 we have shown that the electron relaxation in a quantum dot dimer due to the ICD mechanism is on a picoseconds timescale (PRB 83, 113303) and therefore IR QD detectors based on ICD seems to be feasible. Here we discuss the possibility to observe electron relaxation in QWs. In QWs the effective mass of the electron is not continuous, and can affect the lifetime of the ICD process. In order for the ICD to be the dominant decay mechanism, it must prevail over all other possible competitive decay processes. We have found in our setup that the ICD lifetime is on the timescale of picoseconds. An enhancement of the ICD process occurs when the ionized electron temporarily trapped in a shape-type resonance in the continuum. An experiment based on our findings is currently in progress. In this talk another possibility to observe the ICD phenomenon in two coupled QWs is proposed, by transferring an electron through a two coupled quantum wells structure populated by only one electron. An enhancement in the electron transmission would be obtained when the energy of the incoming electrons allows them to be temporarily trapped inside one of the two quantum wells via the ICD mechanism.

  5. Quantum well states in Rashba semiconductor BiTeI

    NASA Astrophysics Data System (ADS)

    He, Yang; Zhu, Zhihuai; Hamidian, Mohammad; Chen, Pengcheng; Yam, Yau Chuen; Hoffman, Jennifer

    BiTeI displays large Rashba-type spin splitting in both valence and conduction bands. In this work, we use scanning tunneling microscopy to reveal the bipolar nature of BiTeI, confirming the previously observed p-n junction electronic structure. We also discover two-dimensional quantum well states both below and above the semiconducting gap on the Te-terminated surface. This work sheds light on the origin of the giant Rashba splitting in the system. This effort is funded by the NSF Grant DMR-1410480.

  6. Thermopower enhancement in quantum wells with the Rashba effect

    SciTech Connect

    Wu, Lihua; Yang, Jiong; Wang, Shanyu; Wei, Ping; Yang, Jihui E-mail: wqzhang@mail.sic.ac.cn; Zhang, Wenqing E-mail: wqzhang@mail.sic.ac.cn; Chen, Lidong

    2014-11-17

    We theoretically demonstrate that the thermopower in two-dimensional quantum wells (QWs) can be significantly enhanced by its Rashba spin-splitting effect, governed by the one-dimensional density of states in the low Fermi energy region. The thermopower enhancement is due to the lower Fermi level for a given carrier concentration in Rashba QWs, as compared with that in normal two-dimensional systems without the spin-splitting effect. The degenerate approximation directly shows that larger strength of Rashba effect leads to higher thermopower and consequently better thermoelectric performance in QWs.

  7. Reliability assessment of multiple quantum well avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Yun, Ilgu; Menkara, Hicham M.; Wang, Yang; Oguzman, Isamil H.; Kolnik, Jan; Brennan, Kevin F.; May, Gray S.; Wagner, Brent K.; Summers, Christopher J.

    1995-01-01

    The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

  8. Infrared supercontinuum generation in multiple quantum well nanostructures

    NASA Astrophysics Data System (ADS)

    Borgohain, Nitu; Belić, Milivoj; Konar, S.

    2016-11-01

    The paper presents a theoretical study of broadband mid-infrared supercontinuum generation at low power in semiconductor multiple quantum wells (MQWs) facilitated by electromagnetically induced transparency. Pulses of 200 W peak power and 700 fs duration at 9.963 μm have been used to study the supercontinuum generation dynamics in a 1.374 μm long MQW system. The supercontinuum spectrum is 13.0 μm broad and asymmetric about the pump wavelength. Although the spectral broadening is dominated by self-phase modulation, four-wave mixing, modulation instability and soliton generation also contribute to the broadening.

  9. Binding energies of indirect excitons in double quantum well systems

    NASA Astrophysics Data System (ADS)

    Rossokhaty, Alex; Schmult, Stefan; Dietsche, Werner; von Klitzing, Klaus; Kukushkin, Igor

    2011-03-01

    A prerequisite towards Bose-Einstein condensation is a cold and dense system of bosons. Indirect excitons in double GaAs/AlGaAs quantum wells (DQWs) are believed to be suitable candidates. Indirect excitons are formed in asymmetric DQW structures by mass filtering, a method which does not require external electric fields. The exciton density and the electron-hole balance can be tuned optically. Binding energies are measured by a resonant microwave absorption technique. Our results show that screening of the indirect excitons becomes already relevant at densities as low as ~ 5 × 109 cm-2 and results in their destruction.

  10. Strong photoluminescence emission from resonant Fibonacci quantum wells.

    PubMed

    Chang, C H; Chen, C H; Hsueh, W J

    2013-06-17

    Strong photoluminescence (PL) emission from a resonant Fibonacci quantum well (FQW) is demonstrated. The maximum PL intensity in the FQW is significantly stronger than that in a periodic QW under the Bragg or anti-Bragg conditions. Moreover, the peaks of the squared electric field in the FQW are located very near each of the QWs. The optimal PL spectrum in the FQW has an asymmetrical form rather than the symmetrical one in the periodic case. The maximum PL intensity and the corresponding thickness filling factor in the FQW become greater with increasing generation order. PMID:23787654

  11. Highly efficient metallic optical incouplers for quantum well infrared photodetectors.

    PubMed

    Liu, Long; Chen, Yu; Huang, Zhong; Du, Wei; Zhan, Peng; Wang, Zhenlin

    2016-01-01

    Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (Ez) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |Ez|(2) ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors. PMID:27456691

  12. Highly efficient metallic optical incouplers for quantum well infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Liu, Long; Chen, Yu; Huang, Zhong; Du, Wei; Zhan, Peng; Wang, Zhenlin

    2016-07-01

    Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (Ez) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |Ez|2 ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors.

  13. Highly efficient metallic optical incouplers for quantum well infrared photodetectors

    PubMed Central

    Liu, Long; Chen, Yu; Huang, Zhong; Du, Wei; Zhan, Peng; Wang, Zhenlin

    2016-01-01

    Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (Ez) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |Ez|2 ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors. PMID:27456691

  14. Mid- and Long-IR Broadband Quantum Well Photodetector

    NASA Technical Reports Server (NTRS)

    Soibel, Alexander; Ting, David Z.; Khoshakhlagh, Arezou; Gunapala, Sarath D.

    2012-01-01

    A single-stack broadband quantum well infrared photodetector (QWIP) has been developed that consists of stacked layers of GaAs/AlGaAs quantum wells with absorption peaks centered at various wavelengths spanning across the 9- to-11- m spectral regions. The correct design of broadband QWIPs was a critical step in this task because the earlier implementation of broadband QWIPs suffered from a tuning of spectral response curve with an applied bias. Here, a new QWIP design has been developed to overcome the spectral tuning with voltage that results from non-uniformity and bias variation of the electrical field across the detector stacks with different absorption wavelengths. In this design, a special effort has been made to avoid non-uniformity and bias tuning by changing the doping levels in detector stacks to compensate for variation of dark current generation rate across the stacks with different absorption wavelengths. Single-pixel photodetectors were grown, fabricated, and tested using this new design. The measured dark current is comparable with the dark measured current for single-color QWIP detectors with similar cutoff wavelength, thus indicating high material quality as well as absence of performance degradation resulting from broadband design. The measured spectra clearly demonstrate that the developed detectors cover the desired special range of 8 to 12 m. Moreover, the shape of the spectral curves does not change with applied biases, thus overcoming the problem plaguing previous designs of broadband QWIPs.

  15. Quantum Well Thermoelectrics for Converting Waste Heat to Electricity

    SciTech Connect

    Saeid Ghamaty

    2007-04-01

    Fabrication development of high efficiency quantum well (QW) thermoelectric continues with the P-type and N-type Si/Si{sub 80}Ge{sub 20} films with encouraging results. These films are fabricated on Si substrates and are being developed for low as well as high temperature operation. Both isothermal and gradient life testing are underway. One couple has achieved over 4000 hours at T{sub H} of 300 C and T{sub C} of 50 C with little or no degradation. Emphasis is now shifting towards couple and module design and fabrication, especially low resistance joining between N and P legs. These modules can be used in future energy conversion systems as well as for air conditioning.

  16. Quantum capacitance of an HgTe quantum well as an indicator of the topological phase

    NASA Astrophysics Data System (ADS)

    Kernreiter, T.; Governale, M.; Zülicke, U.

    2016-06-01

    Varying the quantum-well width in an HgTe/CdTe heterostructure allows for realizing normal and inverted semiconducting band structures, making it a prototypical system to study two-dimensional (2D) topological-insulator behavior. We have calculated the zero-temperature thermodynamic density of states DT for the electron-doped situation in both regimes, treating interactions within the Hartree-Fock approximation. A distinctively different behavior for the density dependence of DT is revealed in the inverted and normal cases, making it possible to detect the system's topological phase through measurement of macroscopic observables, such as the quantum capacitance or electronic compressibility. Our results establish the 2D electron system in HgTe quantum wells as unique in terms of its collective electronic properties.

  17. Imaging currents in HgTe quantum wells in the quantum spin Hall regime.

    PubMed

    Nowack, Katja C; Spanton, Eric M; Baenninger, Matthias; König, Markus; Kirtley, John R; Kalisky, Beena; Ames, C; Leubner, Philipp; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W; Goldhaber-Gordon, David; Moler, Kathryn A

    2013-09-01

    The quantum spin Hall (QSH) state is a state of matter characterized by a non-trivial topology of its band structure, and associated conducting edge channels. The QSH state was predicted and experimentally demonstrated to be realized in HgTe quantum wells. The existence of the edge channels has been inferred from local and non-local transport measurements in sufficiently small devices. Here we directly confirm the existence of the edge channels by imaging the magnetic fields produced by current flowing in large Hall bars made from HgTe quantum wells. These images distinguish between current that passes through each edge and the bulk. On tuning the bulk conductivity by gating or raising the temperature, we observe a regime in which the edge channels clearly coexist with the conducting bulk, providing input to the question of how ballistic transport may be limited in the edge channels. Our results represent a versatile method for characterization of new QSH materials systems.

  18. Strain dependence on polarization properties of AlGaN and AlGaN-based ultraviolet lasers grown on AlN substrates

    SciTech Connect

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramón; Mita, Seiji; Tweedie, James

    2015-06-08

    Since the band ordering in AlGaN has a profound effect on the performance of UVC light emitting diodes (LEDs) and even determines the feasibility of surface emitting lasers, the polarization properties of emitted light from c-oriented AlGaN and AlGaN-based laser structures were studied over the whole composition range, as well as various strain states, quantum confinements, and carrier densities. A quantitative relationship between the theoretical valence band separation, determined using k•p theory, and the experimentally measured degree of polarization is presented. Next to composition, strain was found to have the largest influence on the degree of polarization while all other factors were practically insignificant. The lowest crossover point from the transverse electric to transverse magnetic polarized emission of 245 nm was found for structures pseudomorphically grown on AlN substrates. This finding has significant implications toward the efficiency and feasibility of surface emitting devices below this wavelength.

  19. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    SciTech Connect

    Xu, Xingsheng

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  20. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Demkov, Alexander; Choi, Miri; Butcher, Matthew; Rodriguez, Cesar; He, Qian; Posadas, Agham; Borisevich, Albina; Zollner, Stefan; Lin, Chungwei; Ortmann, Elliott

    2015-03-01

    We report on the investigation of SrTiO3/LaAlO3 quantum wells (QWs) grown by molecular beam epitaxy (MBE) on LaAlO3 substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized using x-ray photoemission spectroscopy, reflection high-energy electron diffraction (RHEED), scanning transmission electron microscopy (STEM). Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry (SE) in the range of 1.0 eV to 6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells (uc). Density functional theory and tight-binding are used to model the optical response of these heterostructures. Our results demonstrate that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. We acknowledge support from Air Force Office of Scientific Research (FA9550-12-10494).

  1. Trapping and transport of indirect excitons in coupled quantum wells

    NASA Astrophysics Data System (ADS)

    Wuenschell, Jeffrey K.

    Spatially indirect excitons are optically generated composite bosons with a radiative lifetime sufficient to reach thermal equilibrium. This work explores the physics of indirect excitons in coupled quantum wells in the GaAs/AlGaAs system, specifically in the low-temperature, high-density regime. Particular attention is paid to a technique whereby a spatially inhomogeneous strain field is used as a trapping potential. In the process of modeling the trapping profile in wide quantum wells, dramatic effects due to intersubband coupling were observed at high strain. Experimentally, this regime coincides with the abrupt appearance of a dark population of indirect excitons at trap center, an effect originally suspected to be related to Bose-Einstein condensation. Here, the role of band mixing due to the strain-induced distortion of the crystal symmetry will be explored in detail in the context of this effect. Experimental studies presented here and in the literature suggest that Bose-Einstein condensation in indirect exciton systems may be difficult to detect with optical means (e.g., coherence measurements, momentum-space narrowing), possibly due to the strong dipole interaction between indirect excitons. Due to similarities between this system and liquid helium, it may be more fruitful to look for transport-related signatures of condensation, such as super fluidity. Here, a method for performing transport measurements on optically generated indirect excitons is also outlined and preliminary results are presented.

  2. Composition dependent valence band order in c-oriented wurtzite AlGaN layers

    SciTech Connect

    Neuschl, B. Helbing, J.; Knab, M.; Lauer, H.; Madel, M.; Thonke, K.; Feneberg, M.

    2014-09-21

    The valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k∙p theory yields a critical relative aluminum concentration x{sub c}=(0.09±0.05) for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with Γ₉ symmetry of b{sub Γ₉}=0.85eV, and propose a possible bowing for the crystal field energy of b{sub cf}=-0.12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al{sub x}Ga{sub 1-x}N/Al{sub y}Ga{sub 1-y}N quantum well structures is discussed for different compositions.

  3. Efficiency of GaInAs/GaAs quantum-well lasers upon inhomogeneous excitation of quantum wells

    SciTech Connect

    Ushakov, D V; Afonenko, A A; Aleshkin, V Ya

    2013-11-30

    A model for calculating the power characteristics of laser structures taking into account inhomogeneous excitation of quantum wells (QWs), recombination in the barrier regions, and nonlinear gain effects is developed. It is shown that, with increasing number of QWs, the output power of the Ga{sub 0.8}In{sub 0.2}As/GaAs/InGaP structures at first considerably increases and then slightly decreases. In a wide range of injection currents, the optimal number of QWs is 5 ± 1. The inhomogeneity of QW excitation increases with increasing injection current and decreases the laser power compared to homogeneous excitation. (lasers)

  4. Barrier penetration effects on thermopower in semiconductor quantum wells

    SciTech Connect

    Vaidya, R. G.; Sankeshwar, N. S. Mulimani, B. G.

    2014-01-15

    Finite confinement effects, due to the penetration of the electron wavefunction into the barriers of a square well potential, on the low–temperature acoustic-phonon-limited thermopower (TP) of 2DEG are investigated. The 2DEG is considered to be scattered by acoustic phonons via screened deformation potential and piezoelectric couplings. Incorporating the barrier penetration effects, the dependences of diffusion TP and phonon drag TP on barrier height are studied. An expression for phonon drag TP is obtained. Numerical calculations of temperature dependences of mobility and TP for a 10 nm InN/In {sub x}Ga{sub 1−x}N quantum well for different values of x show that the magnitude and behavior of TP are altered. A decrease in the barrier height from 500 meV by a factor of 5, enhances the mobility by 34% and reduces the TP by 58% at 20 K. Results are compared with those of infinite barrier approximation.

  5. Anomalous spin Hall effects in Dresselhaus (110) quantum wells

    NASA Astrophysics Data System (ADS)

    Liu, Ming-Hao; Chang, Ching-Ray

    2010-10-01

    Anomalous spin Hall effects that belong to the intrinsic type in Dresselhaus (110) quantum wells are discussed. For the out-of-plane spin component, antisymmetric current-induced spin polarization induces opposite spin Hall accumulation, even though there is no spin-orbit force due to Dresselhaus (110) coupling. A surprising feature of this spin Hall induction is that the spin accumulation sign does not change upon bias reversal. Contribution to the spin Hall accumulation from the spin Hall induction and the spin deviation due to intrinsic spin-orbit force as well as extrinsic spin scattering can be straightforwardly distinguished simply by reversing the bias. For the in-plane component, inclusion of a weak Rashba coupling leads to a new type of Sy intrinsic spin Hall effect solely due to spin-orbit-force-driven spin separation.

  6. Quantum-well lasers for direct solar photopumping

    NASA Technical Reports Server (NTRS)

    Unnikrishnan, Sreenath; Anderson, Neal G.

    1993-01-01

    Semiconductor lasers directly photopumped by focused sunlight may be viable sources of coherent light for intersatellite communications and other low-power spaceborne applications. In this work, we theoretically explore the possibility of realizing such devices. We specifically assess solar pumped operation of separate-confinement-quantum-well heterostructure (SCQWH) lasers based on InGaAs, GaAs, and AlGaA, as fabrication technology for these lasers is mature and they can operate at very low thresholds. We develop a model for step-index single-well SCQWH lasers photopumped by sunlight, examine how threshold solar photoexcitation intensities depend upon material and structure parameters, design optimum structures for solar-pumped operation, and identify design tradeoffs. Our results suggest that laser action should be possible in properly designed structures at readily achievable solar concentrations and that optimum designs for solar-pumped SCQWH lasers differ significantly from those for analogous current injection devices.

  7. Ge/SiGe quantum well for photonic applications: modelling of the quantum confined Stark effect

    NASA Astrophysics Data System (ADS)

    Isella, Giovanni; Ballabio, Andrea; Frigerio, Jacopo

    2016-05-01

    Ge quantum wells are emerging as a relevant material system for enabling fast and power-efficient optical modulation in the framework of Si-photonics. The need for reliable designs of QW structures, matching given operating wavelengths and bias voltages, calls for the implementation of modelling tools capturing the optical properties of SiGe heterostructures. Here we report on the calculation of the quantum confined Stark effect based on an eight-band k×p model. The obtained spectra are analysed and compared with experimental data showing a good agreement between calculation and measurements.

  8. Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells

    SciTech Connect

    Yang, Wen; Chang, Kai; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    Spin Hall effect can be induced both by the extrinsic impurity scattering and by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. This difference gives a direct mechanism to experimentally distinguish the intrinsic spin Hall effect from the extrinsic one.

  9. Two-band electron transport in a double quantum well

    NASA Astrophysics Data System (ADS)

    Fletcher, R.; Tsaousidou, M.; Smith, T.; Coleridge, P. T.; Wasilewski, Z. R.; Feng, Y.

    2005-04-01

    The carrier densities and mobilities have been measured for the first two populated subbands in a GaAs double quantum well (DQW) as a function of the top gate voltage Vg . The densities and quantum mobilities ( μiq , i=1,2 ) were obtained from the de Haas-Shubnikov oscillations. The transport mobilities (μit) were determined from the semiclassical low-field magnetoresistance with intersubband scattering taken into account. At 0.32K the experimental data on both μit and μiq , as a function of Vg , lie on two curves which cross at the resonance point as expected from theoretical considerations. At 1.09K and 4.2K the μit curves no longer cross at resonance, but show a gap. The reason for this is not known. The mobilities have been calculated in the low-temperature limit within the Boltzmann framework by assuming that they are limited by scattering due to ionized impurities located at the outside interfaces. The assumption of short-range scattering is justified by the relatively small value of the ratio μit/μiq that is measured in the present system. The theoretical values obtained for μit and μiq are in reasonable agreement with the experiment for all values of Vg examined. We have also calculated the resistivity and intersubband scattering rates of the DQW as a function of Vg and again find good agreement with measured values.

  10. Excitons in semiconducting superlattices, quantum wells, and ternary alloys

    SciTech Connect

    Sturge, M.D. . Dept. of Physics); Nahory, R.E.; Tamargo, M.C. )

    1990-08-22

    It is now possible to fabricated semiconducting layered structures with precisely defined layer thicknesses of a few atomic diameters. Examples are the quantum well'' and the superlattice'' structures, in which semiconductors with different band gaps are interleaved. Microstructures'' can be produced from this material by patterning and etching them on a small ({approximately}10nm) scale. Their electronic properties are quite different from those of the constituents and offer interesting new possibilities both in device design and in basic physics. This proposal aims to improve our understanding of optically excited states ( excitons'' and electron-hole plasmas'') in these structures. Work will also continue on ternary alloys, primarily to establish if the alloy disorder produces a mobility edge for excitons, and on II-VI compounds, where the principal interest at present is in the nature of the exciton-phonon coupling.

  11. Photoluminescence characterization of single heterojunction quantum well structures

    NASA Astrophysics Data System (ADS)

    Aina, O.; Mattingly, M.; Juan, F. Y.; Bhattacharya, P. K.

    1987-01-01

    A photoluminescence emission band at 830 nm has been detected in single heterojunction quantum well structures (modulation-doped structures) in the range of 250-400 K. This emission band is observed neither in heterojunction structures without a two-dimensional electron gas (2DEG), nor in n(+) AlGaAs and GaAs. The intensity of the emission band increases as the mobility of the samples with 2DEG and shows excitonic behavior in its variation with incident laser excitation intensity. This photoluminescence emission was observed in samples grown by both molecular beam epitaxy and by organometallic vapor phase epitaxy. This effect may be useful as a rough identification of high quality, modulation-doped heterostructures.

  12. Magnetic quantum well states in ultrathin film and wedge structures

    SciTech Connect

    Li, D.; Bader, S.D.

    1996-04-01

    Magnetic quantum-well (QW) states are probed with angle- and spin-resolved photoemission to address critical issues pertaining to the origin of the giant magnetoresistance (GMR) optimization and oscillatory coupling of magnetic multilayers. Two epitaxial systems are highlighted: Cu/Co(wedge)/Cu(100) and Cr/Fe(100)-whisker. The confinement of Cu sp-QW states by a Co barrier requires a characteristic Co thickness of 2.2 {+-} 0.6 {angstrom}, which is consistent with the interfacial Co thickness reported to optimize the GMR of permalloy-Cu structures. The controversial k-space origin of the 18-{angstrom} long period oscillation in Fe/Cr multilayers is identified by the vector that spans the d-derived lens feature of the Cr Fermi surface, based on the emergence of QW states with 17 {+-} 2 {angstrom} periodicity in this region.

  13. Dark current mechanism of terahertz quantum-well photodetectors

    SciTech Connect

    Jia, J. Y.; Gao, J. H.; Hao, M. R.; Wang, T. M.; Shen, W. Z.; Zhang, Y. H.; Cao, J. C.; Guo, X. G.; Schneider, H.

    2014-10-21

    Dark current mechanisms of terahertz quantum-well photodetectors (THz QWPs) are systematically investigated experimentally and theoretically by measuring two newly designed structures combined with samples reported previously. In contrast to previous investigations, scattering-assisted tunneling dark current is found to cause significant contributions to total dark current. A criterion is also proposed to determine the major dark current mechanism at different peak response frequencies. We further determine background limited performance (BLIP) temperatures, which decrease both experimentally and theoretically as the electric field increases. This work gives good description of dark current mechanism for QWPs in the THz region and is extended to determine the transition fields and BLIP temperatures with response peaks from 3 to 12 THz.

  14. Interplay of Collective Excitations in Quantum Well Intersubband Resonances

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Ning, C. Z.

    2003-01-01

    Intersubband resonances in a semiconductor quantum well (QW) display some of the most fascinating features involving various collective excitations such as Fermi-edge singularity (FES) and intersubband plasmon (ISP). Using a density matrix approach, we treated many-body effects such as depolarization, vertex correction, and self-energy consistently for a two-subband system. We found a systematic change in resonance spectra from FES-dominated to ISP-dominated features, as QW- width or electron density is varied. Such an interplay between FES and ISP significantly changes both line shape and peak position of the absorption spectrum. In particular, we found that a cancellation of FES and ISP undresses the resonant responses and recovers the single-particle features of absorption for semiconductors with a strong nonparabolicity such as InAs, leading to a dramatic broadening of the absorption spectrum.

  15. Ballistic effects and intersubband excitations in multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Schneider, H.; Schönbein, C.; Schwarz, K.; Walther, M.

    1998-07-01

    We have studied the transport properties of electrons in asymmetric quantum well structures upon far-infrared optical excitation of carriers from the lowest subband into the continuum. Here the photocurrent consists of a coherent component originating from ballistic transport upon excitation, and of an incoherent part associated with asymmetric diffusion and relaxation processes, which occur after the coherence has been lost. The signature of the coherent contribution is provided by a sign reversal of the photocurrent upon changing the excitation energy. This sign reversal arises from the energy-dependent interference between continuum states, which have a twofold degeneracy characterized by positive and negative momenta. The interference effect also allows us to estimate the coherent mean free path ( >20 nm at 77K). In specifically designed device structures, we use both the coherent and incoherent components in order to achieve a pronounced photovoltaic infrared response for detector applications.

  16. MOCVD growth of AlGaN UV LEDs

    SciTech Connect

    Han, J.; Crawford, M.H.

    1998-09-01

    Issues related to the MOCVD growth of AlGaN, specifically the gas-phase parasitic reactions among TMG, TMA, and NH{sub 3}, are studied using an in-situ optical reflectometer. It is observed that the presence of the well-known gas phase adduct (TMA: NH{sub 3}) could seriously hinder the incorporation behavior of TMGa. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN SCH QW p-n diode structure. The UV emission at 360 nm (FWHM {approximately} 10 nm) represents the first report of LED operation from an indium-free GaN QW diode.

  17. Improving hole injection and carrier distribution in InGaN light-emitting diodes by removing the electron blocking layer and including a unique last quantum barrier

    SciTech Connect

    Cheng, Liwen Chen, Haitao; Wu, Shudong

    2015-08-28

    The effects of removing the AlGaN electron blocking layer (EBL), and using a last quantum barrier (LQB) with a unique design in conventional blue InGaN light-emitting diodes (LEDs), were investigated through simulations. Compared with the conventional LED design that contained a GaN LQB and an AlGaN EBL, the LED that contained an AlGaN LQB with a graded-composition and no EBL exhibited enhanced optical performance and less efficiency droop. This effect was caused by an enhanced electron confinement and hole injection efficiency. Furthermore, when the AlGaN LQB was replaced with a triangular graded-composition, the performance improved further and the efficiency droop was lowered. The simulation results indicated that the enhanced hole injection efficiency and uniform distribution of carriers observed in the quantum wells were caused by the smoothing and thinning of the potential barrier for the holes. This allowed a greater number of holes to tunnel into the quantum wells from the p-type regions in the proposed LED structure.

  18. Improving hole injection and carrier distribution in InGaN light-emitting diodes by removing the electron blocking layer and including a unique last quantum barrier

    NASA Astrophysics Data System (ADS)

    Cheng, Liwen; Chen, Haitao; Wu, Shudong

    2015-08-01

    The effects of removing the AlGaN electron blocking layer (EBL), and using a last quantum barrier (LQB) with a unique design in conventional blue InGaN light-emitting diodes (LEDs), were investigated through simulations. Compared with the conventional LED design that contained a GaN LQB and an AlGaN EBL, the LED that contained an AlGaN LQB with a graded-composition and no EBL exhibited enhanced optical performance and less efficiency droop. This effect was caused by an enhanced electron confinement and hole injection efficiency. Furthermore, when the AlGaN LQB was replaced with a triangular graded-composition, the performance improved further and the efficiency droop was lowered. The simulation results indicated that the enhanced hole injection efficiency and uniform distribution of carriers observed in the quantum wells were caused by the smoothing and thinning of the potential barrier for the holes. This allowed a greater number of holes to tunnel into the quantum wells from the p-type regions in the proposed LED structure.

  19. Effect of magnetic field on electron spectrum and probabilities of intraband quantum transitions in spherical quantum-dot-quantum-well

    NASA Astrophysics Data System (ADS)

    Holovatsky, V.; Bernik, I.; Yakhnevych, M.

    2016-09-01

    The effect of magnetic field on electron energy spectrum, wave functions and probabilities of intraband quantum transitions in multilayered spherical quantum-dot-quantum-well (QDQW) CdSe/ZnS/CdSe/ZnS is studied. Computations are performed in the framework of the effective mass approximation and rectangular potential barriers model. The wave functions are expanded over the complete basis of functions obtained as exact solutions of the Schrodinger equation for the electron in QDQW without the magnetic field. It is shown that magnetic field takes off the spectrum degeneration with respect to the magnetic quantum number and changes the localization of electron in the nanostructure. The field stronger effects on the spherically-symmetric states, especially in the case of electron location in the outer potential well. The magnetic field changes more the radial distribution of probability of electron location in QDQW than the angular one. The oscillator strengths of intraband quantum transitions are calculated as functions of the magnetic field induction and their selection rules are established.

  20. Intersubband transitions and refractive index changes in coupled double quantum well with different well shapes

    NASA Astrophysics Data System (ADS)

    Ozturk, Emine; Sokmen, Ismail

    2011-10-01

    In this study, both the linear intersubband transitions and the refractive index changes in coupled double quantum well (DQW) with different well shapes for different electric fields are theoretically calculated within framework of the effective mass approximation. Results obtained show that intersubband transitions and the energy levels in coupled DQW can importantly be modified and controlled by the electric field strength and direction. By considering the variation of the energy differences, it should point out that by varying electric field we can obtain a blue or red shift in the intersubband optical transitions. The modulation of the absorption coefficients and the refractive index changes which can be suitable for good performance optical modulators and various infrared optical device applications can be easy obtained by tuning applied electric field strength and direction.

  1. Wavelength-insensitive radiation coupling for multi-quantum well sensor based on intersubband absorption

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D. (Inventor); Bandara, Sumith V. (Inventor); Liu, John K. (Inventor)

    2003-01-01

    Devices and techniques for coupling radiation to intraband quantum-well semiconductor sensors that are insensitive to the wavelength of the coupled radiation. At least one reflective surface is implemented in the quantum-well region to direct incident radiation towards the quantum-well layers.

  2. Wavelength-insensitive radiation coupling for multi-quantum well sensor based on intersubband absorption

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D. (Inventor); Bandara, Sumith V. (Inventor); Liu, John K. (Inventor)

    2006-01-01

    Devices and techniques for coupling radiation to intraband quantum-well semiconductor sensors that are insensitive to the wavelength of the coupled radiation. At least one reflective surface is implemented in the quantum-well region to direct incident radiation towards the quantum-well layers.

  3. Coherent nanocavity structures for enhancement in internal quantum efficiency of III-nitride multiple quantum wells

    SciTech Connect

    Kim, T.; Liu, B.; Smith, R.; Athanasiou, M.; Gong, Y.; Wang, T.

    2014-04-21

    A “coherent” nanocavity structure has been designed on two-dimensional well-ordered InGaN/GaN nanodisk arrays with an emission wavelength in the green spectral region, leading to a massive enhancement in resonance mode in the green spectra region. By means of a cost-effective nanosphere lithography technique, we have fabricated such a structure on an InGaN/GaN multiple quantum well epiwafer and have observed the “coherent” nanocavity effect, which leads to an enhanced spontaneous emission (SE) rate. The enhanced SE rate has been confirmed by time resolved photoluminescence measurements. Due to the coherent nanocavity effect, we have achieved a massive improvement in internal quantum efficiency with a factor of 88, compared with the as-grown sample, which could be significant to bridge the “green gap” in solid-state lighting.

  4. Synthesis and Optical Properties of Colloidal CdS/CdSe/CdS Quantum Wells

    NASA Astrophysics Data System (ADS)

    Hai, Le Ba; Nghia, Nguyen Xuan; Nga, Pham Thu; Chinh, Vu Duc; Linh, Pham Thuy; Trang, Nguyen Thi Thu

    Colloidal CdS/CdSe/CdS quantum wells were synthesized from TOPSe and cadmium oleate in octadecene, a non-coordinating solvent. Absorption, emission, and Raman scattering spectra of colloidal CdS/CdSe/CdS quantum wells with different thickness of CdSe well were investigated. The effect of thickness of CdSe well on the optical and vibrational properties of colloidal CdS/CdSe/CdS quantum wells was discussed. The expri-mental results provide further evidence for the existence of quantum dot-quantum well structures in CdS/CdSe/CdS type materials.

  5. Changes in luminescence emission induced by proton irradiation: InGaAs/GaAs quantum wells and quantum dots

    NASA Technical Reports Server (NTRS)

    Leon, R.; Swift, G. M.; Magness, B.; Taylor, W. A.; Tang, Y. S.; Wang, K. L.; Dowd, P.; Zhang, Y. H.

    2000-01-01

    The photoluminescence emission from InGaAs/GaAs quantum-well and quantum-dot (QD) structures are compared after controlled irradiation with 1.5 MeV proton fluxes. Results presented here show a significant enhancement in radiation tolerance with three-dimensional quantum confinement.

  6. Colloidal graphene quantum dots with well-defined structures.

    PubMed

    Yan, Xin; Li, Binsong; Li, Liang-shi

    2013-10-15

    When the size of a semiconductor crystal is reduced to the nanometer scale, the crystal boundary significantly modifies electron distribution, making properties such as bandgap and energy relaxation dynamics size dependent. This phenomenon, known as quantum confinement, has been demonstrated in many semiconductor materials, leading to practical applications in areas such as bioimaging, photovoltaics, and light-emitting diodes. Graphene, a unique type of semiconductor, is a two-dimensional crystal with a zero bandgap and a zero effective mass of charge carriers. Consequently, we expect new phenomena from nanometer-sized graphene, or graphene quantum dots (QDs), because the energy of charge carriers in graphene follows size-scaling laws that differ from those in other semiconductors. From a chemistry point of view, graphene is made of carbon, an element for which researchers have developed a whole branch of chemistry. Thus, it is possible to synthesize graphene QDs through stepwise, well-controlled organic chemistry, achieving structures with an atomic precision that has not been possible for any other semiconductor materials. Recently, we developed a new solubilizing strategy that led to synthesis of stable colloidal graphene QDs with more than 100 conjugated carbon atoms, allowing us to study their properties in a new size regime. In this Account, we review our recent progress working with the colloidal graphene QDs, including their synthesis and stabilization, tuning of their properties, and new phenomena in energy relaxation dynamics. In particular, we have observed extraordinarily slow "electron cooling"--the relaxation of electrons from high excited states to lower ones. With further investigation, these high-energy electrons could potentially be harvested in solar energy applications, for example, creating more efficient photovoltaic cells. We discuss additional emerging opportunities with these new materials and current challenges, hoping to draw the interest

  7. Ir Wavelength Dependence Quantum Size Effects in Nb/SiO2 Quantum Wells

    NASA Astrophysics Data System (ADS)

    Villagómez, R.

    This letter deals with the experimental observation of oscillations in the infrared reflectance from Nb ultra-thin films deposited on α-type SiO2 substrates. P-polarized reflectance (Rp) measurements are made using a tunable p-polarized CO2 waveguide laser using wavelengths between 9.2 and 10.4 μm. Several Nb/SiO2 quantum wells were specially made by the RF sputtering technique. Tailored thicknesses run between 5.5 and 55 Å. Because of the strong influence from the chosen substrate, IR reflectivity was fitted to the optical response of our metal-substrate system by using the three-oscillator model and numerical calculations on the basis of the local field calculation for a single metallic quantum well. Although quantum size effects are well studied in semiconductor compounds, there are only a few studies of this effect in metallic films where the present investigation has its most important contribution.

  8. III-V semiconductor quantum well and superlattice detectors

    NASA Astrophysics Data System (ADS)

    Walther, Martin; Fuchs, Frank; Schneider, Harald; Fleissner, Joachim; Schmitz, J.; Pletschen, Wilfried; Braunstein, Juergen; Ziegler, Johann; Cabanski, Wolfgang A.; Koidl, Peter; Weimann, Guenter

    1998-10-01

    The paper reviews the development of IR detectors for the 8 - 12 micrometer wavelength range based on GaAs/AlGaAs quantum well structures and InAs/(GaIn)Sb short-period superlattices (SPSLs) at the Fraunhofer-Institute IAF. Photoconductive GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are used for the fabrication of starring IR cameras for thermal imaging in the third atmospheric window. The long wavelength infrared (LWIR) camera, devleoped in cooperation with AEG Infrarot-Module (AIM), consists of a two-dimensional focal plane array (FPA) with 256 X 256 detector elements, flip- chip bonded to a read-out integrated circuit (ROIC). The technology for the fabrication of FPAs, electrical and optical properties of single detector elements in the two-dimensional arrangement and the properties of the LWIR camera system are reported. A noise equivalent temperature difference (NETD) below 10 mK has been measured at an operation temperature of T equals 65 K with an integration time of 20 ms. More than 99.8% of all pixels are working and no cluster defects are observed. InAs/(GaIn)Sb SPSLs with a broken gap type-II band alignment are well suited for the fabrication of IR detectors covering the 3 - 12 micrometer spectral range. Due to the lattice mismatch of the InAs/(GaIn)Sb SPSL with respect to GaSb, tight control of thickness and composition of the layers and a controlled formation of the chemical bonds across the interface in the SPSLs are used for strain compensation. Photodiodes with a cut-off wavelength (lambda) c equals 8 micrometer and a current responsivity R(lambda ) equals 2 A/W exhibit a dynamic impedance of R0A equals 1k(Omega) cm2 at T equals 77 K. This leads to a Johnson- noise limited detectivity in excess of D* equals 1 X 1012 cm(Hz)1/2/W for these type of detectors.

  9. Influence of optical polarization on the improvement of light extraction efficiency from reflective scattering structures in AlGaN ultraviolet light-emitting diodes

    SciTech Connect

    Wierer, J. J. Allerman, A. A.; Montaño, I.; Moseley, M. W.

    2014-08-11

    The improvement in light extraction efficiency from reflective scattering structures in AlGaN ultraviolet light-emitting diodes (UVLEDs) emitting at ∼270 nm is shown to be influenced by optical polarization. Three UVLEDs with different reflective scattering structures are investigated and compared to standard UVLEDs without scattering structures. The optical polarization and therefore the direction of light propagation within the various UVLEDs are altered by changes in the quantum well (QW) thickness. The improvement in light extraction efficiency of the UVLEDs with reflective scattering structures increases, compared to the UVLEDs without scattering structures, as the fraction of emitted light propagating parallel to the QW plane increases. Additionally, the light extraction efficiency increases as the average distance to the reflective scattering structures decreases.

  10. Resonant optical reflection by a periodic system of the quantum well excitons at the second quantum state

    SciTech Connect

    Chaldyshev, V. V.; Poddubny, A. N.; Vasil'ev, A. P.; Chen Yuechao; Liu Zhiheng

    2011-02-14

    A periodic multiple quantum well GaAs/AlGaAs structure was designed, grown, and characterized in order to reveal resonant features in optical spectra when the Bragg resonance was tuned to the second quantum state x(e2-hh2) of the heavy-hole exciton-polaritons in the multiple quantum wells. This double resonance was demonstrated by tuning the incident angle of the light as well as by comparison with a single quantum well structure. A significant enhancement of the light-matter interaction was observed, which manifests itself by strong resonant optical reflection and electroreflection.

  11. On the mechanisms of energy transfer between quantum well and quantum dashes

    NASA Astrophysics Data System (ADS)

    Sek, G.; Kudrawiec, R.; Podemski, P.; Misiewicz, J.; Somers, A.; Höfling, S.; Reithmaier, J. P.; Kamp, M.; Forchel, A.

    2012-08-01

    We investigate energy transfer mechanisms from a quantum well (QW) to quantum dashes (QDashes) separated by a few nanometer thick barrier in InAs/InGaAs/InGaAlAs/InP material system. We show that at sufficiently low temperatures excitons, which are non-resonantly photogenerated in the QW and then transferred to the ground state via phonon relaxation, can be retrieved by QDashes. The excess of the transferred energy, defined by the energy difference between the QW and QDash exciton states, can be dissipated via interaction with LO phonons if the respective energy matching is satisfied. This kind of exciton injection from QW to QDashes is a process insensitive to the energy level structure of the individual exciton components, i.e., electrons and holes. It is shown that within the single particle picture, the electron energy in QDashes is higher by more than 50 meV compared to the corresponding QW energy, which prevents the electron transfer from quantum well to the dashes. We show experimentally that despite this unfavorable energy difference for single carriers whole QW excitons are efficiently transferred to QDashes and recombine there radiatively.

  12. Hysteresis in the quantum Hall regimes in electron double quantum well structures

    NASA Astrophysics Data System (ADS)

    Pan, W.; Reno, J. L.; Simmons, J. A.

    2005-04-01

    We present here experimental results on magnetotransport coefficients in electron double quantum well (DQW) structures. Consistent with previous studies, transport hysteresis is is observed in the electron DQWs. Furthermore, in our gated DQW samples, by varying the top layer Landau level filling (νtop) while maintaining a relatively constant filling factor in the bottom layer (νbot) , we are able to explain the sign of Rxx(up)-Rxx(down) , where Rxx(up) is the magnetoresistance when the gate voltage Vg is swept up and Rxx(down) when Vg is swept down. Interestingly, at small magnetic fields hysteresis is generally stronger when the top quantum well is in the even integer quantum Hall effect (IQHE) regime (e.g., νtop=2 ) than in the odd IQHE regime (e.g, νtop=1 ). While at higher B fields, the hysteresis at νtop=1 becomes the strongest. The switching occurs around the B field at νbot=3 .

  13. Structural and optical investigations of AlGaN MQWs grown on a relaxed AlGaN buffer on AlN templates for emission at 280 nm

    NASA Astrophysics Data System (ADS)

    Li, X.; Le Gac, G.; Bouchoule, S.; El Gmili, Y.; Patriarche, G.; Sundaram, S.; Disseix, P.; Réveret, F.; Leymarie, J.; Streque, J.; Genty, F.; Salvestrini, J.-P.; Dupuis, R. D.; Li, X.-H.; Voss, P. L.; Ougazzaden, A.

    2015-12-01

    10-period Al0.57Ga0.43N/Al0.38Ga0.62N multi-quantum wells (MQWs) were grown on a relaxed Al0.58Ga0.42N buffer on AlN templates on sapphire. The threading dislocations and V-pits were characterized and their origin is discussed. The influence of V-pits on the structural quality of the MQWs and on optical emission at 280 nm was analyzed. It was observed that near-surface V-pits were always associated with grain boundaries consisting of edge threading dislocations originating from the AlN/Al2O3 interface. Although the high density of V-pits disrupted MQWs growth, it did not affect the internal quantum efficiency which was measured to be ~1% at room temperature even when V-pit density was increased from 7×107 cm-2 to 2×109 cm-2. The results help to understand the origin, propagation and influences of the typical defects in AlGaN MQWs grown on AlN/Al2O3 templates which may lead to further improvement of the performance of DUV devices.

  14. Emergence of the Persistent Spin Helix in Semiconductor Quantum Wells

    SciTech Connect

    Koralek, Jake; Weber, Chris; Orenstein, Joe; Bernevig, Andrei; Zhang, Shoucheng; Mack, Shawn; Awschalom, David

    2011-08-24

    According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit (SO) coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be recovered in a two-dimensional electron gas (2DEG), despite the presence of SO coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix' (PSH). SU(2) is restored, in principle, when the strength of two dominant SO interactions, the Rashba ({alpha}) and linear Dresselhaus ({beta}{sub 1}), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term ({beta}{sub 3}) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as {alpha} {yields} {beta}{sub 1}. Here we observe experimentally the emergence of the PSH in GaAs quantum wells (QW's) by independently tuning {alpha} and {beta}{sub 1}. Using transient spin-grating spectroscopy (TSG), we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant SO terms, identifying {beta}{sub 3} as the main SU(2) violating term in our samples. The tunable suppression of spin-relaxation demonstrated in this work is well-suited for application to spintronics.

  15. Study of multiple InAs/GaAs quantum-well structures by electroreflectance spectroscopy

    SciTech Connect

    Bolshakov, A. S. Chaldyshev, V. V. Babichev, A. V.; Kudryashov, D. A.; Gudovskikh, A. S.; Morozov, I. A.; Sobolev, M. S.; Nikitina, E. V.

    2015-11-15

    A periodic Bragg heterostructure with three ultrathin InAs/GaAs quantum wells in a period is fabricated and studied. The splitting energy of exciton transitions in quantum wells is determined by the electroreflectance- spectroscopy method and numerical quantum-mechanical calculation. The significant influence of interference effects on individual peak areas in the electroreflectance spectrum is detected.

  16. Performance improvement of GaN-based near-UV LEDs with InGaN/AlGaN superlattices strain relief layer and AlGaN barrier

    NASA Astrophysics Data System (ADS)

    Jia, Chuanyu; Yu, Tongjun; Feng, Xiaohui; Wang, Kun; Zhang, Guoyi

    2016-09-01

    The carrier confinement effect and piezoelectric field-induced quantum-confined stark effect of different GaN-based near-UV LED samples from 395 nm to 410 nm emission peak wavelength were investigated theoretically and experimentally. It is found that near-UV LEDs with InGaN/AlGaN multiple quantum wells (MQWs) active region have higher output power than those with InGaN/GaN MQWs for better carrier confinement effect. However, as emission peak wavelength is longer than 406 nm, the output power of the near-UV LEDs with AlGaN barrier is lower than that of the LEDs with GaN barrier due to more serious spatial separation of electrons and holes induced by the increase of piezoelectric field. The N-doped InGaN/AlGaN superlattices (SLs) were adopted as a strain relief layer (SRL) between n-GaN and MQWs in order to suppress the polarization field. It is demonstrated the output power of near-UV LEDs is increased obviously by using SLs SRL and AlGaN barrier for the discussed emission wavelength range. Besides, the forward voltage of near-UV LEDs with InGaN/AlGaN SLs SRL is lower than that of near-UV LEDs without SRL.

  17. Many-Body Effects in Quantum-Well Intersubband Transitions

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Ning, Cun-Zheng

    2003-01-01

    Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (Qw) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons (ISPs). The oscillator strength of intersubband transitions (ISBTs) strongly varies with QW parameters and electron density because of this coupling. We have developed a set of kinetic equations, termed the intersubband semiconductor Bloch equations (ISBEs), from density matrix theory with the Hartree-Fock approximation, that enables a consistent description of these many-body effects. Using the ISBEs for a two-conduction-subband model, various many-body effects in intersubband transitions are studied in this work. We find interesting spectral changes of intersubband absorption coefficient due to interplay of the Fermi-edge singularity, subband renormalization, intersubband plasmon oscillation, and nonparabolicity of bandstructure. Our results uncover a new perspective for ISBTs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBT line shape.

  18. Commercialization of quantum well infrared photodetector focal plane arrays

    NASA Astrophysics Data System (ADS)

    Kukkonen, C. A.; Sirangelo, M. N.; Chehayeb, R.; Kaufmann, M.; Liu, J. K.; Rafol, S. B.; Gunapala, S. D.

    2001-06-01

    Many commercial and government applications need high performance, large format, long-wavelength infrared (LWIR) detector arrays in the range of 6-20 μm. NASA and the ballistic missile defense organization (BMDO) have devoted a significant effort to develop highly sensitive infrared (IR) detectors and large format focal plane arrays (FPAs) based on novel 'artificial' low effective bandgap semiconductor material systems such as GaAs/AlGaAs. Caltech's Jet propulsion laboratory (JPL) under contract from NASA and BMDO has extensively pursued GaAs/AlGaAs based multi-quantum wells (MQWs) for IR radiation detection. Optimization of the detector design, light coupling schemes, large format FPA fabrication and packaging techniques have culminated in the realization of portable LWIR cameras with a mid format (256×256 pixel) FPA of QWIP detectors and the demonstration of TV format (i.e., 640×486) QWIP camera. QWIP technologies LLC, under an exclusive agreement with Caltech is currently manufacturing the QWIP-Chip TM, a 320×256 element FPA. In this, presentation, we will discuss the advantages of MQW technology and our experience in the commercialization of QWIP FPAs.

  19. Quantum well infrared photodetector simultaneously working in two atmospheric windows

    NASA Astrophysics Data System (ADS)

    Huo, Y. H.; Ma, W. Q.; Zhang, Y. H.; Chen, L. H.; Shi, Y. L.

    2010-08-01

    We have demonstrated a two-contact quantum well infrared photodetector (QWIP) exhibiting simultaneous photoresponse in both the mid- and the long-wavelength atmospheric windows of 3-5 μm and of 8-12 μm. The structure of the device was achieved by sequentially growing a mid-wavelength QWIP part followed by a long-wavelength QWIP part separated by an n-doped layer. Compared with the conventional dual-band QWIP device utilizing three ohmic contacts, our QWIP is promising to greatly facilitate two-color focal plane array (FPA) fabrication by reducing the number of the indium bumps per pixel from three to one just like a monochromatic FPA fabrication and to increase the FPA fill factor by reducing one contact per pixel; another advantage may be that this QWIP FPA boasts broadband detection capability in the two atmospheric windows while using only a monochromatic readout integrated circuit. We attributed this simultaneous broadband detection to the different distributions of the total bias voltage between the mid- and long-wavelength QWIP parts.

  20. Terahertz quantum-well photodetectors: Design, performance, and improvements

    SciTech Connect

    Zhang, S. Wang, T. M.; Hao, M. R.; Yang, Y.; Zhang, Y. H.; Shen, W. Z.; Liu, H. C.

    2013-11-21

    Theoretical studies and numerical simulations on design, performance, and improvements of terahertz quantum-well photodetector (THz QWP) are presented. In the first part of this paper, we discuss the device band structure resulting from a self-consistent solution and simulation results. First, the temperature dependence of device characteristics is analyzed. Next, we deduce the condition of optimal doping concentration for maximizing dark current limited detectivity D{sub det}* when QWP is lightly doped. Accordingly, unlike in previously published reports, doping concentration is not fixed and is selected by the above condition. In the second part of this paper, we propose two schemes for improving operation temperature. The first is to incorporate an optical antenna which focuses incident THz wave. Numerical results show that the QWP with peak frequency higher than 5.5 THz is expected to achieve background-noise-limited performance at 77 K or above when employing a 10{sup 6} times enhancement antenna. The second scheme is to use a laser as the signal source to achieve photon-noise-limited performance (PLIP) at high temperatures. Simulations show that when operating below critical temperature QWPs in the range of 1 ∼ 7 THz can reach PLIP under practical illumination intensities.

  1. Blue and green electroluminescence from CdSe nanocrystal quantum-dot-quantum-wells

    SciTech Connect

    Lu, Y. F.; Cao, X. A.

    2014-11-17

    CdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique, and their optical properties were tuned by bandgap and strain engineering. 3-monolayer (ML) CdSe QWs emitted blue photoluminescence at 467 nm with a spectral full-width-at-half-maximum of ∼30 nm. With a 3 ML ZnS cladding layer, which also acts as a passivating and strain-compensating layer, the QDQWs acquired a ∼35% quantum yield of the QW emission. Blue and green electroluminescence (EL) was obtained from QDQW light-emitting devices with 3–4.5 ML CdSe QWs. It was found that as the peak blueshifted, the overall EL was increasingly dominated by defect state emission due to poor hole injection into the QDQWs. The weak EL was also attributed to strong field-induced charge separation resulting from the unique QDQW geometry, weakening the oscillator strength of optical transitions.

  2. Quantum spin Hall effect in α -Sn /CdTe(001 ) quantum-well structures

    NASA Astrophysics Data System (ADS)

    Küfner, Sebastian; Matthes, Lars; Bechstedt, Friedhelm

    2016-01-01

    The electronic and topological properties of heterovalent and heterocrystalline α -Sn/CdTe(001) quantum wells (QWs) are studied in dependence on the thickness of α -Sn by means of ab initio calculations. We calculate the topological Z2 invariants of the respective bulk crystals, which identify α -Sn as strong three-dimensional (3D) topological insulators (TIs), whereas CdTe is a trivial insulator. We predict the existence of two-dimensional (2D) topological interface states between both materials and show that a topological phase transition from a trivial insulating phase into the quantum spin Hall (QSH) phase in the QW structures occurs at much higher thicknesses than in the HgTe case. The QSH effect is characterized by the localization, dispersion, and spin polarization of the topological interface states. We address the distinction of the 3D and 2D TI characters of the studied QW structures, which is inevitable for an understanding of the underlying quantum state of matter. The 3D TI nature is characterized by two-dimensional topological interface states, while the 2D phase exhibits one-dimensional edge states. The two different state characteristics are often intermixed in the discussion of the topology of 2D QW structures, especially, the comparison of ab initio calculations and experimental transport studies.

  3. Quantum Hall effect in HgTe quantum wells at nitrogen temperatures

    SciTech Connect

    Kozlov, D. A. Kvon, Z. D.; Mikhailov, N. N.; Dvoretskii, S. A.; Weishäupl, S.; Krupko, Y.; Portal, J.-C.

    2014-09-29

    We report on the observation of quantized Hall plateaus in a system of two-dimensional Dirac fermions, implemented in a 6.6 nm HgTe quantum well at magnetic fields up to 34 T at nitrogen temperatures. The activation energies determined from the temperature dependence of the longitudinal resistivity are found to be almost equal for the filling factors ν of 1 and 2. This indicates that the large values of the g-factor (about 30–40) remain unchanged at very strong magnetic fields.

  4. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty; Sal Marchetti

    2005-03-03

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices.

  5. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty; Sal Marchetti

    2004-05-10

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices.

  6. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty; Sal Marchetti

    2004-07-30

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices.

  7. The energy-level crossing behavior and quantum Fisher information in a quantum well with spin-orbit coupling

    PubMed Central

    Wang, Z. H.; Zheng, Q.; Wang, Xiaoguang; Li, Yong

    2016-01-01

    We study the energy-level crossing behavior in a two-dimensional quantum well with the Rashba and Dresselhaus spin-orbit couplings (SOCs). By mapping the SOC Hamiltonian onto an anisotropic Rabi model, we obtain the approximate ground state and its quantum Fisher information (QFI) via performing a unitary transformation. We find that the energy-level crossing can occur in the quantum well system within the available parameters rather than in cavity and circuit quantum eletrodynamics systems. Furthermore, the influence of two kinds of SOCs on the QFI is investigated and an intuitive explanation from the viewpoint of the stationary perturbation theory is given. PMID:26931762

  8. Picosecond intersubband hole relaxation in p-type quantum wells

    SciTech Connect

    Xu, Z.; Fauchet, P.M.; Rella, C.W.; Schwettman, H.A.

    1995-12-31

    We report the first direct measurement of the relaxation time of holes in p-type quantum wells using tunable, subpicosecond mid-infrared laser pulses in a pump-probe arrangement. The QW layers consisted of 50 In{sub 0.5}Ga{sub 0.5}As/Al{sub 0.5}Ga{sub 0.5}As periods. The In{sub 0.5}Ga{sub 0.5}As well was 4 nm wide and the Al{sub 0.5}Ga{sub 0.5}As barrier was 8 nm wide. The dopant concentration was 10{sup 19} CM{sup -3} which corresponds to a sheet density of 1.2 x 10{sup 13} CM{sup -2}. The room temperature IR spectrum showed a 50 meV wide absorption peak at 5.25 {mu}m (220 meV). This energy agrees with the calculated n=1 heavy hole to n=1 light hole transition energy of 240 meV (150 meV for strain and 90 meV for confinement). The large absorption width results from hole-hole scattering and the difference in dispersion relations between the two subbands. The equal-wavelength pump-probe transmission measurements were performed using the Stanford free electron laser (FEL). The FEL pulses were tuned between 4 and 6 {mu} m and their duration was less than 1 ps. The measurements were performed as a function of temperature, pump wavelength and intensity (from 0.3 to 10 GW/cm{sup 2}). In all our experiments, we find an increase of transmission (decrease of absorption or bleaching) following photopumping, which recovers as a single exponential with a time constant (relaxation time) of the order of 1 picosecond. The maximum change in transmission is linear with pump 2 intensity below 1 GW/cm{sup 2} and saturates to {approximately}3% with a saturation intensity I{sub sat} of 3 GW/cm{sup 2}. As the saturation regime is entered, the relaxation time increases from 0.8 ps to 1.8 ps. This relaxation time depends on the temperature T: it increases from 0.8 ps to 1.3 ps as T decreases from 300 K to 77 K. Finally, when we tune the laser through the absorption band, the magnitude of the signal changes but its temporal behavior does not change, within the accuracy of the measurements.

  9. Quantum Hall effect in an InAs /AlSb double quantum well

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Podgornykh, S. M.; Sadofyev, Yu. G.

    2009-01-01

    Double quantum wells (DQWs) were first implemented in the InAs /AlSb heterosystem, which is characterized by a large Landé g factor ∣g∣=15 of the InAs layers forming the well, much larger than the bulk g factor ∣g∣=0.4 of the GaAs in conventional GaAs /AlGaAs DQWs. The quality of the samples is good enough to permit observation of a clear picture of the quantum Hall effect (QHE). Despite the small tunneling gap, which is due to the large barrier height (1.4eV), features with odd filling factors ν =3,5,7,… are present in the QHE, due to collectivized interlayer states of the DQW. When the field is rotated relative to the normal to the layers, the ν =3 state is suppressed, confirming the collectivized nature of that state and denying that it could owe its existence to a strong asymmetry of the DQW. Previously the destruction of the collectivized QHE states by a parallel field had been observed only for the ν =1 state. The observation of a similar effect for ν =3 in an InAs /AlSb DQW may be due to the large bulk g factor of InAs.

  10. Minimized open-circuit voltage reduction in GaAs/InGaAs quantum well solar cells with bandgap-engineered graded quantum well depths

    SciTech Connect

    Li, Xiaohan; Dasika, Vaishno D.; Li, Ping-Chun; Ji, Li; Bank, Seth R.; Yu, Edward T.

    2014-09-22

    The use of InGaAs quantum wells with composition graded across the intrinsic region to increase open-circuit voltage in p-i-n GaAs/InGaAs quantum well solar cells is demonstrated and analyzed. By engineering the band-edge energy profile to reduce photo-generated carrier concentration in the quantum wells at high forward bias, simultaneous increases in both open-circuit voltage and short-circuit current density are achieved, compared to those for a structure with the same average In concentration, but constant rather than graded quantum well composition across the intrinsic region. This approach is combined with light trapping to further increase short-circuit current density.

  11. Analysis of the influence of external magnetic field on transition matrix elements in quantum well and quantum cascade laser structures

    NASA Astrophysics Data System (ADS)

    Demić, Aleksandar; Radovanović, Jelena; Milanović, Vitomir

    2016-08-01

    We present a method for modeling nonparabolicity effects (NPE) in quantum nanostructures in presence of external electric and magnetic field by using second order perturbation theory. The method is applied to analysis of quantum well structure and active region of a quantum cascade laser (QCL). This model will allow us to examine the influence of magnetic field on dipole matrix element in QCL structures, which will provide a better insight to how NPE can affect the gain of QCL structures.

  12. Self organized growth of doped vertical quantum wells for normal incidence intersubband transitions

    NASA Astrophysics Data System (ADS)

    Berger, V.; Vermeire, G.; Demeester, P.; Weisbuch, C.

    1996-06-01

    The self-organized growth of N-doped vertical AlGaAs quantum wells by metalorganic vapor phase epitaxy of a single doped AlGaAs layer on a submicron grating is described. Intersubband absorption at normal incidence is demonstrated in those vertical quantum wells. This opens new possibilities for infrared quantum well devices using intersubband transitions, including normal incidence infrared modulators.

  13. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty

    2005-07-01

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce the technology for fabricating a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices. In this quarter Hi-Z has continued fabrication of the QW films and also continued development of joining techniques for fabricating the N and P legs into a couple. The upper operating temperature limit for these films is unknown and will be determined via the isothermal aging studies that are in progress. We are reporting on these studies in this report. The properties of the QW films that are being evaluated are Seebeck, thermal conductivity and thermal-to-electricity conversion efficiency.

  14. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty

    2006-03-31

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce the technology for fabricating a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices. In this quarter Hi-Z has continued fabrication of the QW films and also continued development of joining techniques for fabricating the N and P legs into a couple. The upper operating temperature limit for these films is unknown and will be determined via the isothermal aging studies that are in progress. We are reporting on these studies in this report. The properties of the QW films that are being evaluated are Seebeck, thermal conductivity and thermal-to-electricity conversion efficiency.

  15. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty

    2006-02-01

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce the technology for fabricating a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices. In this quarter Hi-Z has continued fabrication of the QW films and also continued development of joining techniques for fabricating the N and P legs into a couple. The upper operating temperature limit for these films is unknown and will be determined via the isothermal aging studies that are in progress. We are reporting on these studies in this report. The properties of the QW films that are being evaluated are Seebeck, thermal conductivity and thermal-to-electricity conversion efficiency.

  16. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty

    2005-05-01

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce the technology for fabricating a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices. In this quarter Hi-Z has continued fabrication of the QW films and also continued development of joining techniques for fabricating the N and P legs into a couple. The upper operating temperature limit for these films is unknown and will be determined via the isothermal aging studies that are in progress. We are reporting on these studies in this report. The properties of the QW films that are being evaluated are Seebeck, thermal conductivity and thermal-to-electricity conversion efficiency.

  17. QUANTUM WELL THERMOELECTRICS FOR CONVERTING WASTE HEAT TO ELECTRICITY

    SciTech Connect

    Saeid Ghamaty

    2004-01-01

    New thermoelectric materials using Quantum Well (QW) technology are expected to increase the energy conversion efficiency to more than 25% from the present 5%, which will allow for the low cost conversion of waste heat into electricity. Hi-Z Technology, Inc. has been developing QW technology over the past six years. It will use Caterpillar, Inc., a leader in the manufacture of large scale industrial equipment, for verification and life testing of the QW films and modules. Other members of the team are Pacific Northwest National Laboratory, who will sputter large area QW films. The Scope of Work is to develop QW materials from their present proof-of-principle technology status to a pre-production level over a proposed three year period. This work will entail fabricating the QW films through a sputtering process of 50 {micro}m thick multi layered films and depositing them on 12 inch diameter, 5 {micro}m thick Si substrates. The goal in this project is to produce the technology for fabricating a basic 10-20 watt module that can be used to build up any size generator such as: a 5-10 kW Auxiliary Power Unit (APU), a multi kW Waste Heat Recovery Generator (WHRG) for a class 8 truck or as small as a 10-20 watt unit that would fit on a daily used wood fired stove and allow some of the estimated 2-3 billion people on earth, who have no electricity, to recharge batteries (such as a cell phone) or directly power radios, TVs, computers and other low powered devices. In this quarter Hi-Z has continued fabrication of the QW films and also continued development of joining techniques for fabricating the N and P legs into a couple. The upper operating temperature limit for these films is unknown and will be determined via the isothermal aging studies that are in progress. We are reporting on these studies in this report. The properties of the QW films that are being evaluated are Seebeck, thermal conductivity and thermal-to-electricity conversion efficiency.

  18. Cathodoluminescence from II-VI quantum well light emitting diodes

    NASA Astrophysics Data System (ADS)

    Nikiforov, Alexey Yuriyevich

    The objectives of the present research were to advance understanding of luminescence degradation, defects, and bias-dependent carrier confinement and transport in ZnCd(Mg)Se-based quantum well (QW) LED structures grown by molecular beam epitaxy. Most data were obtained from three LED samples. One was a ZnCdSe QW-based red LED with Au coating on top, and two were ZnCdMgSe QW-based blue LEDs with Au coating or Au dots on top. Optical and carrier confinement properties were characterized by time-resolved and bias-dependent cathodoluminescence (CL) spectroscopy and imaging. Electrical behavior was characterized by I-V and electroluminescence (EL) measurements. Both reversible and irreversible effects of bias and electron bombardment on luminescence were observed. Reversible effects were QW CL energy shifts and QW CL intensity changes during bias cycling. No EL was detected from the blue LEDs. Irreversible effects were QW CL decreases for the red LED and QW CL intensity enhancements for the blue LEDs. Reversible effects of bias on CL were simulated using a model incorporating generation and transport of excess carriers, overlap of the electron and hole wave functions, carrier escape, and competition between radiative and nonradiative processes. Ground state energy levels of carriers in the QW heterostructure were calculated in the effective mass and envelope function approximations. Modification of energy levels and wave functions by bias was calculated for both infinite and finite QWs. The finite QW simulations predict the reversible bias-dependent CL intensity behaviors seen experimentally for both red and blue LEDs. The simulations predict qualitatively, but not quantitatively, the reversible photon energy shifts with bias for the red LED. The photon energy shifts for the blue LEDs differed in both direction and magnitude from the simulations. The CL experiments have not established the cause of irreversible intensity decreases observed for the red LED during

  19. Effect of thickness and carrier density on the optical polarization of Al{sub 0.44}Ga{sub 0.56}N/Al{sub 0.55}Ga{sub 0.45}N quantum well layers

    SciTech Connect

    Wierer, J. J. Montaño, I.; Crawford, M. H.; Allerman, A. A.

    2014-05-07

    The thickness and carrier density of AlGaN quantum well (QW) layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. An ultraviolet-emitting (270–280 nm) multiple quantum well heterostructure consisting of 3 periods of Al{sub 0.44}Ga{sub 0.56}N/Al{sub 0.55}Ga{sub 0.45}N with individual layer thicknesses between 2–3.2 nm is studied both experimentally and theoretically. The optical polarization changes to preferentially polarized perpendicular to the QW plane as the QW thickness increases or the carrier density increases. Calculations show these trends are due to (a) a larger decrease in overlap of conduction band to light and heavy hole envelope functions compared to crystal-field split-off envelope functions, and (b) coupling between the valence subbands where higher heavy hole subbands couple to lower light hole and crystal-field split-off subbands. These changes in the valence band have a profound effect on the optical polarization, emission patterns, and eventual light extraction for ultraviolet emitters at these compositions and thicknesses, and need to be controlled to ensure high device efficiency.

  20. Photoluminescence excitation spectroscopy of excited states of an asymmetric cubic GaN/Al0.25Ga0.75N double quantum well grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wecker, Tobias; Callsen, Gordon; Hoffmann, Axel; Reuter, Dirk; As, Donat J.

    2016-05-01

    Optical transitions involving higher energy levels of cubic AlGaN quantum wells are investigated by means of photoluminescence excitation spectroscopy. An asymmetric cubic GaN/Al x Ga1- x N double quantum well (QW) structure with an Al content of x = 0.25 ± 0.03 was grown on a 3C-SiC(001) substrate exploiting radio-frequency plasma-assisted molecular beam epitaxy. The photoluminescence excitation data reveals two emission bands, which are assigned to the first electron and the third heavy hole (e1-hh3) and the second electron and the second heavy hole (e2-hh2) energy level of the wide QW. Besides in the narrow QW no higher energy levels can be observed. The experimental data is in good agreement with theoretical calculations using a Schrödinger-Poisson solver based on an effective mass model (nextnano3). The exciton binding energy was calculated considering the confinement of the QWs and also the energy dependency of the effective mass for excited energy levels.

  1. Strong coupling and polariton lasing in Te based microcavities embedding (Cd,Zn)Te quantum wells

    SciTech Connect

    Rousset, J.-G. Piętka, B.; Król, M.; Mirek, R.; Lekenta, K.; Szczytko, J.; Borysiuk, J.; Suffczyński, J.; Kazimierczuk, T.; Goryca, M.; Smoleński, T.; Kossacki, P.; Nawrocki, M.; Pacuski, W.

    2015-11-16

    We report on properties of an optical microcavity based on (Cd,Zn,Mg)Te layers and embedding (Cd,Zn)Te quantum wells. The key point of the structure design is the lattice matching of the whole structure to MgTe, which eliminates the internal strain and allows one to embed an arbitrary number of unstrained quantum wells in the microcavity. We evidence the strong light-matter coupling regime already for the structure containing a single quantum well. Embedding four unstrained quantum wells results in further enhancement of the exciton-photon coupling and the polariton lasing in the strong coupling regime.

  2. Dynamic light-matter coupling across multiple spatial dimensions in a quantum dots-in-a-well heterostructure

    SciTech Connect

    Prasankumar, Rohit P; Taylor, Antoinette J

    2009-01-01

    Ultrafast density-dependent optical spectroscopic measurements on a quantum dots-in-a-well heterostructure reveal several distinctive phenomena, most notably a strong coupling between the quantum well population and light absorption at the quantum dot excited state.

  3. A Planar Quantum Transistor Based on 2D-2D Tunneling in Double Quantum Well Heterostructures

    SciTech Connect

    Baca, W.E.; Blount, M.A.; Hafich, M.J.; Lyo, S.K.; Moon, J.S.; Reno, J.L.; Simmons, J.A.; Wendt, J.R.

    1998-12-14

    We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate-control of two-dimensional -- two-dimensional (2D-2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally-defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch (EBASE) flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 microns can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I-V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets ({approximately} 21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain, and high-speed.

  4. THz photoresponse of quantum Hall devices based on HgTe-Quantum wells

    NASA Astrophysics Data System (ADS)

    Gouider, F.; Hein, G.; Brüne, C.; Buhmann, H.; Vasilyev, Yu. B.; Nachtwei, G.

    2010-01-01

    This study concerns the experimental investigation of the Terahertz -(THz-) photoresponse in systems under quantum-Hall-(QH-) conditions. These investigations are interesting regarding a potential application of QH-systems as fast and spectrally sensitive THz-detectors. The measurements of the THz-photoresponse (PR) of devices with HgTe quantum wells (QWs) embedded in CdHgTe barriers are aimed at obtaining photosignals at smaller magnetic fields in comparison to detectors made of GaAs/AlGaAs wafers. This can be realized by changing the electron density (application of a gate electrode). The QWs have a thickness of dQW between 7 nm and 12 nm, so that the material HgTe of the QW possesses a semimetallic band structure. We found a cyclotron mass of about mc = 0.026 m0 for our samples from cyclotron resonance measurements (also approximately determined from our PR). As this cyclotron mass is by about a factor 3 smaller than the one of electrons in GaAs, the same Landau level splitting is reached at about 1/3 of the magnetic field as in GaAs.

  5. Enhancement of carrier lifetimes in type-II quantum dot/quantum well hybrid structures

    NASA Astrophysics Data System (ADS)

    Couto, O. D. D.; de Almeida, P. T.; dos Santos, G. E.; Balanta, M. A. G.; Andriolo, H. F.; Brum, J. A.; Brasil, M. J. S. P.; Iikawa, F.; Liang, B. L.; Huffaker, D. L.

    2016-08-01

    We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL) measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness.

  6. Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

    SciTech Connect

    Iida, Daisuke; Fadil, Ahmed Ou, Yiyu; Kopylov, Oleksii; Ou, Haiyan; Chen, Yuntian; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

    2015-09-15

    We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm{sup 2}, and a factor of 8.1 at 1 W/cm{sup 2}. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.

  7. Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

    NASA Technical Reports Server (NTRS)

    Levine, B. F.; Zussman, A.; Gunapala, S. D.; Asom, M. T.; Kuo, J. M.; Hobson, W. S.

    1992-01-01

    We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

  8. An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

    SciTech Connect

    Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A.; Zvonkov, B. N.; Kudryavtsev, K. E.; Nekorkin, S. M.

    2015-02-15

    A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

  9. The Double-Well Potential in Quantum Mechanics: A Simple, Numerically Exact Formulation

    ERIC Educational Resources Information Center

    Jelic, V.; Marsiglio, F.

    2012-01-01

    The double-well potential is arguably one of the most important potentials in quantum mechanics, because the solution contains the notion of a state as a linear superposition of "classical" states, a concept which has become very important in quantum information theory. It is therefore desirable to have solutions to simple double-well potentials…

  10. Designs of blue and green light-emitting diodes based on type-II InGaN-ZnGeN2 quantum wells

    NASA Astrophysics Data System (ADS)

    Han, Lu; Kash, Kathleen; Zhao, Hongping

    2016-09-01

    Type-II InGaN-ZnGeN2 quantum wells (QWs) are studied as improved active regions for light-emitting diodes emitting in the blue (λ ˜ 485 nm) and green (λ ˜ 530 nm) spectral ranges. Both the energy band gap and the lattice parameters of ZnGeN2 are very close to those of GaN. The recently predicted large band offset between GaN and ZnGeN2 allows the formation of a type-II InGaN-ZnGeN2 heterostructure. The strong confinement of holes in the ZnGeN2 layer allows the use of a lower In-content InGaN QW to extend the emission wavelength into the blue and green wavelength regions, as compared to the traditional InGaN QW with uniform In content. In the type-II InGaN-ZnGeN2 QW designs, a thin AlGaN layer was used as a barrier for better carrier confinement. The type-II InGaN-ZnGeN2 QWs lead to a significant enhancement of the electron-hole wave function overlap as compared to those of the conventional QWs. Simulation studies of the proposed type-II QWs promise a significant enhancement of the spontaneous emission rate by 6.1-7.2 times for the QW design emitting at the blue wavelength region and 4.6-4.9 times for the QW design emitting at the green wavelength region, as compared to the conventional InGaN QWs emitting at the same wavelengths.

  11. Advantages of an indirect semiconductor quantum well system for infrared detection

    NASA Technical Reports Server (NTRS)

    Yang, Chan-Lon; Somoano, Robert; Pan, Dee-Son

    1989-01-01

    The infrared intersubband absorption process in quantum well systems with anisotropic bulk effective masses, which usually occurs in indirect semiconductors was analyzed. It is found that the anisotropic effective mass can be utilized to provide allowed intersubband transitions at normal incidence to the quantum well growth direction. This transition is known to be forbidden for cases of isotropic effective mass. This property can be exploited for infrared sensor application of quantum well structures by allowing direct illumination of large surface areas without using special waveguide structures. The 10-micron intersubband absorption in quantum wells made of the silicon-based system Si/Si(1-x)Ge(x) was calculated. It is found that it is readily possible to achieve an absorption constant of the order of 10,000/cm in these Si quantum wells with current doping technology.

  12. Excitonic luminescence of SiGe/Si quantum wells δ-doped with boron

    SciTech Connect

    Bagaev, V. S.; Nikolaev, S. N.; Onishchenko, E. E.; Pruchkina, A. A.; Krivobok, V. S.; Novikov, A. V.

    2015-05-14

    Low-temperature photoluminescence of undoped and moderately δ-doped Si{sub 1−x}Ge{sub x}/Si (x < 0.1) quantum wells has been studied. The influence of boron δ-layer on the excitonic luminescence and the luminescence caused by a dense electron plasma was demonstrated. The conditions under which the luminescence spectra of quantum wells are dominated by impurity-bound excitons (BE) have been established. Some unusual properties of these BE are explained in terms of type II band-offset in Si{sub 1−x}Ge{sub x}/Si (x < 0.1) quantum wells, which favors a spatial separation of electrons and holes. It is shown that the temperature dependence of an excitonic emission in the quantum wells allows to calculate the BE-related density of states and, thus, can be used for contactless estimation of the impurity concentration in quantum wells.

  13. Single-dot optical emission from ultralow density well-isolated InP quantum dots

    SciTech Connect

    Ugur, A.; Hatami, F.; Masselink, W. T.; Vamivakas, A. N.; Lombez, L.; Atatuere, M.

    2008-10-06

    We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/{mu}m{sup 2} is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

  14. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    SciTech Connect

    Malinverni, M. Lamy, J.-M.; Martin, D.; Grandjean, N.; Feltin, E.; Dorsaz, J.; Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C.

    2014-12-15

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH{sub 3}-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10{sup −4} Ω cm{sup 2}, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH{sub 3}-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm{sup 2} ridge dimension and a threshold current density of ∼5 kA cm{sup −2} in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al{sub 0.06}Ga{sub 0.94}N:Mg despite the low growth temperature.

  15. High-efficiency blue LEDs with thin AlGaN interlayers in InGaN/GaN MQWs grown on Si (111) substrates

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeya; Yoshida, Hisashi; Ito, Toshihide; Okada, Aoi; Uesugi, Kenjiro; Nunoue, Shinya

    2016-02-01

    We demonstrate high-efficiency blue light-emitting diodes (LEDs) with thin AlGaN interlayers in InGaN/GaN multiquantum wells (MQWs) grown on Si (111) substrates. The peak external quantum efficiency (EQE) ηEQE of 82% at room temperature and the hot/cold factor (HCF) of 94% have been obtained by using the functional thin AlGaN interlayers in the MQWs in addition to reducing threading dislocation densities (TDDs) in the blue LEDs. An HCF is defined as ηEQE(85°C)/ηEQE(25°C). The blue LED structures were grown by metal-organic chemical vapor deposition on Si (111) substrates. The MQWs applied as an active layer have 8- pairs of InGaN/AlyGa1-yN/GaN (0<=y<=1) heterostructures. Thinfilm LEDs were fabricated by removing the Si (111) substrates from the grown layers. It is observed by high-resolution transmission electron microscopy and three-dimensional atom probe analysis that the 1 nm-thick AlyGa1-yN interlayers, whose Al content is y=0.3 or less, are continuously formed. EQE and the HCFs of the LEDs with thin Al0.15Ga0.85N interlayers are enhanced compared with those of the samples without the interlayers in the low-current-density region. We consider that the enhancement is due to both the reduction of the nonradiative recombination centers and the increase of the radiative recombination rate mediated by the strain-induced hole carriers indicated by the simulation of the energy band diagram.

  16. Observation of a fractional quantum Hall state at v=1/4 in a wide GaAs quantum well.

    SciTech Connect

    Pan, Wei; Tsui, Daniel Chee; Baldwin, K. W.; West, Ken W.; Pfeiffer, Loren N.; Luhman, D. R.

    2008-10-01

    We report the observation of an even-denominator fractional quantum Hall state at {nu}=1/4 in a high quality, wide GaAs quantum well. The sample has a quantum well width of 50 nm and an electron density of n{sub e}=2.55 x 10{sup 11} cm{sup -2}. We have performed transport measurements at T{approx}35 mK in magnetic fields up to 45 T. When the sample is perpendicular to the applied magnetic field, the diagonal resistance displays a kink at {nu}=1/4. Upon tilting the sample to an angle of {theta}=20.3{sup o} a clear fractional quantum Hall state emerges at {nu}=1/4 with a plateau in the Hall resistance and a strong minimum in the diagonal resistance.

  17. A study of non-equilibrium phonons in GaAs/AlAs quantum wells

    SciTech Connect

    Su, Zhenpeng

    1996-11-01

    In this thesis we have studied the non-equilibrium phonons in GaAs/AlAs quantum wells via Raman scattering. We have demonstrated experimentally that by taking into account the time-reversal symmetry relation between the Stokes and anti-Stokes Raman cross sections, one can successfully measure the non-equilibrium phonon occupancy in quantum wells. Using this technique, we have studied the subject of resonant intersubband scattering of optical phonons. We find that interface roughness plays an important role in resonant Raman scattering in quantum wells. The lateral size of the smooth regions in such interface is estimated to be of the order of 100 {Angstrom}. Through a study of photoluminescence of GaAs/AlAs quantum wells under high intensity laser excitation, we have found that band nonparabolicity has very little effect on the electron subband energies even for subbands as high as a few hundred meV above the lowest one. This finding may require additional theoretical study to understand its origin. We have also studied phonon confinement and propagation in quantum wells. We show that Raman scattering of non-equilibrium phonons in quantum wells can be a sensitive measure of the spatial extent of the longitudinal optical (LO) phonons. We deduce the coherence length of LO phonons in GaAs/Al{sub x}Ga{sub 1-x}As quantum wells as a function of the Al concentration x.

  18. Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells

    SciTech Connect

    Cabrera, C. I.; Enciso, A.; Contreras-Solorio, D. A.; Hernandez, L.; Connolly, J. P.

    2014-04-28

    Strain-balanced quantum well solar cells (SB-QWSCs) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a p–i–n device. Anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. The addition of a distributed Bragg reflector can substantially increase the photocurrent while decreasing the radiative recombination current. We have examined the impact of the photon recycling effect on SB-QWSC performance. We have optimized SB-QWSC design to achieve single junction efficiencies above 30%.

  19. Well width dependence of gain and threshold current in GaAlAs single quantum well lasers

    SciTech Connect

    Saint-Cricq, B.; Lozes-Dupuy, F.; Vassilieff, G.

    1986-05-01

    The optical gain of single quantum well GaAs/GaAlAs laser diodes is studied theoretically. The model uses a no k-selection rule and Fermi statistics to obtain the gain coefficient expression. Gain-current characteristics are then reported and allow comparison of structures with well widths between 50 and 400 A. Comparison is also made to previous models which use a strict k-selection rule. The theoretical threshold current densities are calculated for typical single quantum well lasers where the optical confinement is performed using a five-layer slab waveguide. They are shown to be relatively insensitive to the well width as long as L/sub Z/ is larger than 80 A. Comparison between two different structures shows that optical confinement plays a critical role for optimizing the threshold current and should be carefully studied, especially if the k-selection rule is relaxed.

  20. Interface-Driven Ferromagnetism within the Quantum Wells of a Rare Earth Titanate Superlattice.

    PubMed

    Need, R F; Isaac, B J; Kirby, B J; Borchers, J A; Stemmer, S; Wilson, Stephen D

    2016-07-15

    Here we present polarized neutron reflectometry measurements exploring thin film heterostructures composed of a strongly correlated Mott state, GdTiO_{3}, embedded with SrTiO_{3} quantum wells. Our results reveal that the net ferromagnetism inherent to the Mott GdTiO_{3} matrix propagates into the nominally nonmagnetic SrTiO_{3} quantum wells and tracks the magnetic order parameter of the host Mott insulating matrix. Beyond a well thickness of 5 SrO layers, the magnetic moment within the wells is dramatically suppressed, suggesting that quenched well magnetism comprises the likely origin of quantum critical magnetotransport in this thin film architecture. Our data demonstrate that the interplay between proximate exchange fields and polarity-induced carrier densities can stabilize extended magnetic states within SrTiO_{3} quantum wells. PMID:27472135

  1. Interface-Driven Ferromagnetism within the Quantum Wells of a Rare Earth Titanate Superlattice

    NASA Astrophysics Data System (ADS)

    Need, R. F.; Isaac, B. J.; Kirby, B. J.; Borchers, J. A.; Stemmer, S.; Wilson, Stephen D.

    2016-07-01

    Here we present polarized neutron reflectometry measurements exploring thin film heterostructures composed of a strongly correlated Mott state, GdTiO3 , embedded with SrTiO3 quantum wells. Our results reveal that the net ferromagnetism inherent to the Mott GdTiO3 matrix propagates into the nominally nonmagnetic SrTiO3 quantum wells and tracks the magnetic order parameter of the host Mott insulating matrix. Beyond a well thickness of 5 SrO layers, the magnetic moment within the wells is dramatically suppressed, suggesting that quenched well magnetism comprises the likely origin of quantum critical magnetotransport in this thin film architecture. Our data demonstrate that the interplay between proximate exchange fields and polarity-induced carrier densities can stabilize extended magnetic states within SrTiO3 quantum wells.

  2. Microwave spectroscopic observation of distinct electron solid phases in wide quantum wells.

    PubMed

    Hatke, A T; Liu, Yang; Magill, B A; Moon, B H; Engel, L W; Shayegan, M; Pfeiffer, L N; West, K W; Baldwin, K W

    2014-06-20

    In high magnetic fields, two-dimensional electron systems can form a number of phases in which interelectron repulsion plays the central role, since the kinetic energy is frozen out by Landau quantization. These phases include the well-known liquids of the fractional quantum Hall effect, as well as solid phases with broken spatial symmetry and crystalline order. Solids can occur at the low Landau-filling termination of the fractional quantum Hall effect series but also within integer quantum Hall effects. Here we present microwave spectroscopy studies of wide quantum wells that clearly reveal two distinct solid phases, hidden within what in d.c. transport would be the zero diagonal conductivity of an integer quantum-Hall-effect state. Explanation of these solids is not possible with the simple picture of a Wigner solid of ordinary (quasi) electrons or holes.

  3. Microwave spectroscopic observation of distinct electron solid phases in wide quantum wells

    PubMed Central

    Hatke, A. T.; Liu, Yang; Magill, B. A.; Moon, B. H.; Engel, L. W.; Shayegan, M.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.

    2014-01-01

    In high magnetic fields, two-dimensional electron systems can form a number of phases in which interelectron repulsion plays the central role, since the kinetic energy is frozen out by Landau quantization. These phases include the well-known liquids of the fractional quantum Hall effect, as well as solid phases with broken spatial symmetry and crystalline order. Solids can occur at the low Landau-filling termination of the fractional quantum Hall effect series but also within integer quantum Hall effects. Here we present microwave spectroscopy studies of wide quantum wells that clearly reveal two distinct solid phases, hidden within what in d.c. transport would be the zero diagonal conductivity of an integer quantum-Hall-effect state. Explanation of these solids is not possible with the simple picture of a Wigner solid of ordinary (quasi) electrons or holes. PMID:24948190

  4. Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes

    SciTech Connect

    Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan

    2011-07-14

    The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.

  5. Energy transformation of plasmonic photocatalytic oxidation on 1D quantum well of platinum thin film

    NASA Astrophysics Data System (ADS)

    Huang, Hung Ji; Liu, Bo-Heng

    2015-12-01

    The energy transformation of vertical incident light into energy for a chemical reaction is demonstrated in the endothermic oxidation of ammonium ions in a spinning disk reactor. The plasmonic enhancement on photocatalytic reaction demonstrated the generation of quantum hot charge on 1D quantum well of platinum thin film.

  6. Radiation Effects in Nanostructures: Comparison of Proton Irradiation Induced Changes on Quantum Dots and Quantum Wells

    NASA Technical Reports Server (NTRS)

    Leon, R.; Swift, G.; Magness, B.; Taylor, W.; Tang, Y.; Wang, K.; Dowd, P.; Zhang, Y.

    2000-01-01

    Successful implementation of technology using self-forming semiconductor Quantum Dots (QDs) has already demonstrated that temperature independent Dirac-delta density of states can be exploited in low current threshold QD lasers and QD infrared photodetectors.

  7. Nonlinearity from quantum mechanics: Dynamically unstable Bose-Einstein condensate in a double-well trap

    SciTech Connect

    Javanainen, Juha

    2010-05-15

    We study theoretically an atomic Bose-Einstein condensate in a double-well trap, both quantum-mechanically and classically, under conditions such that in the classical model an unstable equilibrium dissolves into large-scale oscillations of the atoms between the potential wells. Quantum mechanics alone does not exhibit such nonlinear dynamics, but measurements of the atom numbers in the potential wells may nevertheless cause the condensate to behave essentially classically.

  8. Intersubband absorption of silicon-based quantum wells for infrared imaging

    NASA Technical Reports Server (NTRS)

    Yang, Chan-Ion; Pan, Dee-Son

    1988-01-01

    The 10-micron intersubband absorption in quantum wells made of the silicon-based system, Si/Si(1-x)Ge(x), has been calculated. The necessary details of the effective-mass anisotropy are included in the present analysis. It is found that it is readily possible to achieve an absorption constant of order of 10,000/cm in Si quantum wells with current doping technology. For 110-line and 111-line growth directions, a further advantage of Si quantum wells is pointed out, namely, an allowed absorption at normal incidence due to the anisotropic effective mass in Si.

  9. Analytical method for determining quantum well exciton properties in a magnetic field

    NASA Astrophysics Data System (ADS)

    Stépnicki, Piotr; Piétka, Barbara; Morier-Genoud, François; Deveaud, Benoît; Matuszewski, Michał

    2015-05-01

    We develop an analytical approximate method for determining the Bohr radii of Wannier-Mott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variational-perturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through exciton-polariton experiments realized in a GaAs/AlAs microcavity with an 8 nm InxGa1 -xAs quantum well and magnetic field strengths as high as 14 T.

  10. Mid-infrared intersubband absorption from p-Ge quantum wells grown on Si substrates

    NASA Astrophysics Data System (ADS)

    Gallacher, K.; Ballabio, A.; Millar, R. W.; Frigerio, J.; Bashir, A.; MacLaren, I.; Isella, G.; Ortolani, M.; Paul, D. J.

    2016-02-01

    Mid-infrared intersubband absorption from p-Ge quantum wells with Si0.5Ge0.5 barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness. Fourier transform infra-red transmission and photoluminescence measurements demonstrate clear absorption peaks corresponding to intersubband transitions among confined hole states. The work indicates an approach that will allow quantum well intersubband photodetectors to be realized on Si substrates in the important atmospheric transmission window of 8-13 μm.

  11. Bethe-Salpeter equation for quantum-well exciton states in an inhomogeneous magnetic field

    NASA Astrophysics Data System (ADS)

    Koinov, Z. G.; Nash, P.; Witzel, J.

    2003-04-01

    The trapping of excitons in a single quantum well due to the presence of a strong homogeneous magnetic field and a weak inhomogeneous cylindrical symmetric magnetic field, created by the deposition of a magnetized disk on top of the quantum well, both applied perpendicular to the x-y plane of confinement is studied theoretically. The numerical calculations are performed for GaAs/AlxGa1-xAs quantum wells and the formation of bound exciton states with nonzero values for the center-of-mass exciton wave function only in a small area is predicted.

  12. Bethe-Salpeter equation for exciton states in quantum well in a nonhomogeneous magnetic field

    NASA Astrophysics Data System (ADS)

    Koinov, Z.; Nash, P.; Witzel, J.

    2003-03-01

    The trapping of excitons in a single quantum well due to the presence of an external strong constant magnetic field and a small nonhomogeneous cylindrical symmetric magnetic field, created by a magnetized disk on top of the quantum well, is studied by applying the Bethe-Salpeter formalism. The numerical calculations are performed for GaAs/AlGaAs quantum wells. We find that the nonhomogeneous magnetic field leads to the formation of bound exciton states with nonzero values for the center-of-mass exciton wave function only in a sufficiently small area.

  13. Intersubband Transition in GaN/InGaN Multiple Quantum Wells

    PubMed Central

    Chen, G.; Wang, X. Q.; Rong, X.; Wang, P.; Xu, F. J.; Tang, N.; Qin, Z. X.; Chen, Y. H.; Shen, B.

    2015-01-01

    Utilizing the growth temperature controlled epitaxy, high quality GaN/In0.15Ga0.85N multiple quantum wells designed for intersubband transition (ISBT) as novel candidates in III-nitride infrared device applications have been experimentally realized for the first time. Photo-absorption originated from the ISBT has been successfully observed at infrared regime covering the 3–5 μm atmosphere window, where the central absorption wavelength is modulated by adjusting the quantum well width. With increasing the quantum well thickness, the ISBT center wave length blue shifts at thickness less than 2.8 nm and then redshifts with further increase of the well thickness. The non-monotonic trend is most likely due to the polarization induced asymmetric shape of the quantum wells. PMID:26089133

  14. Diamagnetic susceptibility of a hydrogenic donor in a group IV-VI quantum dot-quantum well heterostructure

    NASA Astrophysics Data System (ADS)

    Saravanamoorthy, S. N.; Peter, A. John

    2016-05-01

    Electronic properties of a hydrogenic donor impurity in a CdSe/Pb0.8Cd0.2Se/CdSe quantum dot quantum well system are investigated for various radii of core with shell materials. Confined energies are obtained taking into account the geometrical size of the system and thereby the donor binding energies are found. The diamagnetic susceptibility is estimated for a confined shallow donor in the well system. The results show that the diamagnetic susceptibility strongly depends on core and shell radii and it is more sensitive to variations of the geometrical size of the well material.

  15. Simulation of a broadband nano-biosensor based on an onion-like quantum dot-quantum well structure

    NASA Astrophysics Data System (ADS)

    Absalan, H.; SalmanOgli, A.; Rostami, R.

    2013-07-01

    The fluorescence resonance energy transfer is studied between modified quantum-dots and quantum-wells used as a donor and an acceptor. Because of the unique properties of quantum dots, including diverse surface modification flexibility, bio-compatibility, high quantum yields and wide absorption, their use as nano-biosensors and bio-markers used in diagnosis of cancer is suggested. The fluorescence resonance energy transfer is simulated in a quantum dot-quantum well system, where the energy can flow from donor to acceptor. If the energy transfer can be either turned on or off by a specific interaction, such as interaction with any dyes, a molecular binding event or a cleavage reaction, a sensor can be designed (under assumption that the healthy cells have a known effect or unyielding effect on output parameters while cancerous cells, due to their pandemic optical properties, can impact the fluorescence resonance energy transfer parameters). The developed nano-biosensor can operate in a wide range of wavelengths (310 - 760 nm).

  16. Simulation of a broadband nano-biosensor based on an onion-like quantum dot-quantum well structure

    SciTech Connect

    Absalan, H; SalmanOgli, A; Rostami, R

    2013-07-31

    The fluorescence resonance energy transfer is studied between modified quantum-dots and quantum-wells used as a donor and an acceptor. Because of the unique properties of quantum dots, including diverse surface modification flexibility, bio-compatibility, high quantum yields and wide absorption, their use as nano-biosensors and bio-markers used in diagnosis of cancer is suggested. The fluorescence resonance energy transfer is simulated in a quantum dot-quantum well system, where the energy can flow from donor to acceptor. If the energy transfer can be either turned on or off by a specific interaction, such as interaction with any dyes, a molecular binding event or a cleavage reaction, a sensor can be designed (under assumption that the healthy cells have a known effect or unyielding effect on output parameters while cancerous cells, due to their pandemic optical properties, can impact the fluorescence resonance energy transfer parameters). The developed nano-biosensor can operate in a wide range of wavelengths (310 - 760 nm). (laser applications in biology and medicine)

  17. Ultrafast Photodetection in the Quantum Wells of Single AlGaAs/GaAs-Based Nanowires

    NASA Astrophysics Data System (ADS)

    Erhard, N.; Zenger, S.; Morkötter, S.; Rudolph, D.; Weiss, M.; Krenner, H. J.; Karl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G.; Holleitner, A. W.

    2015-10-01

    We investigate the ultrafast optoelectronic properties of single Al0.3Ga0.7As/GaAs-core-shell-nanowires. The nanowires contain GaAs-based quantum wells. For a resonant excitation of the quantum wells, we find a picosecond photocurrent which is consistent with an ultrafast lateral expansion of the photogenerated charge carriers. This Dember-effect does not occur for an excitation of the GaAs-based core of the nanowires. Instead, the core exhibits an ultrafast displacement current and a photo-thermoelectric current at the metal Schottky contacts. Our results uncover the optoelectronic dynamics in semiconductor core-shell nanowires comprising quantum wells, and they demonstrate the possibility to use the low-dimensional quantum well states therein for ultrafast photoswitches and photodetectors.

  18. Two-dimensional electron gas in monolayer InN quantum wells

    SciTech Connect

    Pan, W. E-mail: e.dimakis@hzdr.de; Wang, G. T.; Dimakis, E. E-mail: e.dimakis@hzdr.de; Moustakas, T. D.; Tsui, D. C.

    2014-11-24

    We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in a superlattice structure of 40 InN quantum wells consisting of one monolayer of InN embedded between 10 nm GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 5 × 10{sup 15 }cm{sup −2} (or 1.25 × 10{sup 14 }cm{sup −2} per InN quantum well, assuming all the quantum wells are connected by diffused indium contacts) and 420 cm{sup 2}/Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES.

  19. Comparative analysis of hole transport in compressively strained InSb and Ge quantum well heterostructures

    SciTech Connect

    Agrawal, Ashish; Barth, Michael; Madan, Himanshu; Datta, Suman; Lee, Yi-Jing; Lin, You-Ru; Wu, Cheng-Hsien; Ko, Chih-Hsin; Wann, Clement H.; Loubychev, Dmitri; Liu, Amy; Fastenau, Joel; Lindemuth, Jeff

    2014-08-04

    Compressively strained InSb (s-InSb) and Ge (s-Ge) quantum well heterostructures are experimentally studied, with emphasis on understanding and comparing hole transport in these two-dimensional confined heterostructures. Magnetotransport measurements and bandstructure calculations indicate 2.5× lower effective mass for s-InSb compared to s-Ge quantum well at 1.9 × 10{sup 12} cm{sup –2}. Advantage of strain-induced m* reduction is negated by higher phonon scattering, degrading hole transport at room temperature in s-InSb quantum well compared to s-Ge heterostructure. Consequently, effective injection velocity is superior in s-Ge compared to s-InSb. These results suggest s-Ge quantum well heterostructure is more favorable and promising p-channel candidate compared to s-InSb for future technology node.

  20. Quantum phases of bosons in double-well optical lattices

    SciTech Connect

    Danshita, I.; Williams, J. E.; Melo, C. A. R. sa de; Clark, C. W.

    2007-10-15

    We study the superfluid and insulating phases of bosons in double-well optical lattices, and focus on the specific example of a two-legged ladder, which is currently accessible in experiments. We obtain the zero-temperature phase diagram using both mean-field and time-evolving block decimation techniques. We find that the mean-field approach describes the correct phase boundaries only when the intrachain hopping is sufficiently small in comparison to the on-site repulsion. We show the dependence of the phase diagram on the interchain hopping or tilt between double wells. We find that the Mott-insulator phase at unit filling exhibits a nonmonotonic behavior as a function of the tilt parameter, producing a reentrant phase transition between Mott insulator and superfluid phases. Finally, we determine the critical point separating the insulating and superfluid phases at commensurate fillings, where the Berezinskii-Kosterlitz-Thouless transition occurs.

  1. Resonant spin and valley polarization in ferromagnetic silicene quantum well

    SciTech Connect

    Wang, Yu

    2014-01-20

    We propose a silicene-based lateral resonant tunneling device by placing silicene under the modulation of top nonmagnetic/ferromagnetic/nonmagnetic sandwich nanogates. Following the electric-tunable bandgap of silicene, lateral double-barrier structure is formed by imposing the flexible electrostatic modulation on top gates. By aligning the spin and valley-resolved confined states in magnetic well, remarkable spin/valley polarization can be accessed through spinor-relying resonant tunneling mechanism. Under the electrostatic, magnetic, and size manipulation, the confined well state can be efficiently engineered, and the observed spin and valley polarization can be further flexibly tuned, offering some helpful strategies to construct spinor-electronic logic atomically.

  2. Enhanced current injection from a quantum well to a quantum dash in magnetic field

    NASA Astrophysics Data System (ADS)

    Paravicini-Bagliani, Gian L.; Liverini, Valeria; Valmorra, Federico; Scalari, Giacomo; Gramm, Fabian; Faist, Jérôme

    2014-08-01

    Resonant tunneling injection is a key ingredient in achieving population inversion in a putative quantum dot cascade laser. In a quantum dot based structure, such resonant current requires a matching of the wavefunction shape in k-space between the injector and the quantum dot. We show experimentally that the injection into an excited state of a dash structure can be enhanced tenfold by an in-plane magnetic field that shifts the injector distribution in k-space. These experiments, performed on resonant tunneling diode structures, show unambiguously resonant tunneling into an ensemble of InAs dashes grown between two AlInAs barrier layers. They also show that interface roughness scattering can enhance the tunneling current.

  3. Energy transfer processes in ZnSe/(Zn,Mn)Se double quantum wells

    NASA Astrophysics Data System (ADS)

    Jankowski, Stephanie; Horst, Swantje; Chernikov, Alexej; Chatterjee, Sangam; Heimbrodt, Wolfram

    2009-10-01

    The complex interplay of energy transfer and tunneling processes in a series of asymmetric ZnSe/(Zn,Mn)Se double quantum-well (DQW) structures is investigated. Steady-state and time-resolved photoluminescence at low temperatures and external magnetic fields up to 7 T in this system show remarkable differences to earlier studies on CdTe/(Cd,Mn)Te DQWs. The pure quantum-mechanical tunneling process is only a minor contribution to the magnetic field dependence of the emission even in case of small barriers and strong QW coupling. The experimental results are supported by quantum-well calculations.

  4. Electron transfer and capture dynamics in ZnSe quantum wells grown on GaAs

    SciTech Connect

    Dongol, A.; Wagner, H. P.

    2013-12-04

    We investigate the transfer and capture dynamics of electrons in phase coherent photorefractive ZnSe quantum wells grown on GaAs using degenerate three-beam four-wave-mixing. The measurements reveal electron capture times by the quantum well in the order of several tens of picoseconds and a transit time of approximately 5 picoseconds from the GaAs substrate through the ZnMgSe barrier.

  5. Quantum Well Intrasubband Photodetector for Far Infared and Terahertz Radiation Detection

    NASA Technical Reports Server (NTRS)

    Ting, David Z. -Y.; Chang, Yia-Chung; Bandara, Sumith V.; Gunapala, Sarath D.

    2007-01-01

    The authors present a theoretical analysis on the possibility of using the dopant-assisted intrasubband absorption mechanism in quantum wells for normal-incidence far infrared/terahertz radiation detection. The authors describe the proposed concept of the quantum well intrasubband photodetector (QWISP), which is a compact semiconductor heterostructure device compatible with existing GaAs focal-plane array technology, and present theoretical results demonstrating strong normal-incidence absorption and responsivity in the QWISP.

  6. Transmission line model for strained quantum well lasers including carrier transport and carrier heating effects.

    PubMed

    Xia, Mingjun; Ghafouri-Shiraz, H

    2016-03-01

    This paper reports a new model for strained quantum well lasers, which are based on the quantum well transmission line modeling method where effects of both carrier transport and carrier heating have been included. We have applied this new model and studied the effect of carrier transport on the output waveform of a strained quantum well laser both in time and frequency domains. It has been found that the carrier transport increases the turn-on, turn-off delay times and damping of the quantum well laser transient response. Also, analysis in the frequency domain indicates that the carrier transport causes the output spectrum of the quantum well laser in steady state to exhibit a redshift which has a narrower bandwidth and lower magnitude. The simulation results of turning-on transients obtained by the proposed model are compared with those obtained by the rate equation laser model. The new model has also been used to study the effects of pump current spikes on the laser output waveforms properties, and it was found that the presence of current spikes causes (i) wavelength blueshift, (ii) larger bandwidth, and (iii) reduces the magnitude and decreases the side-lobe suppression ratio of the laser output spectrum. Analysis in both frequency and time domains confirms that the new proposed model can accurately predict the temporal and spectral behaviors of strained quantum well lasers. PMID:26974607

  7. Electro-physical characteristics of MIS structures with HgTe- based single quantum wells

    NASA Astrophysics Data System (ADS)

    Dzyadukh, S.; Nesmelov, S.; Voitsekhovskii, A.; Gorn, D.

    2015-12-01

    The paper presents brief research results of the admittance of metal-insulator- semiconductor (MIS) structures based on Hg1-xCdxTe grown by molecular-beam epitaxy (MBE) method including single HgCdTe/HgTe/HgCdTe quantum wells (QW) in the surface layer. The thickness of a quantum well was 5.6 nm, and the composition of barrier layers with the thickness of 35 nm was close to 0.65. Measurements were conducted in the range of temperatures from 8 to 200 K. It is shown that for structure with quantum well based on HgTe capacitance and conductance oscillations in the strong inversion are observed. Also it is assumed these oscillations are related with the recharging of quantum levels in HgTe.

  8. 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

  9. Negative Differential Transconductance in Silicon Quantum Well MOSFET/Bipolar Hybrid Transistors

    NASA Astrophysics Data System (ADS)

    Naquin, Clint; Lee, Mark; Edwards, Hal; Chatterjee, Tathagata; Mathur, Guru; Maggio, Ken; Univ of Texas, Dallas/Texas Instruments Collaboration

    2015-03-01

    Introducing explicit quantum transport into Si transistors in a manner amenable to industrial fabrication has proven challenging. Hybrid field-effect / bipolar Si transistors fabricated on an industrial 45 nm process line are shown to demonstrate explicit quantum transport signatures. These transistors incorporate a lateral ion implantation-defined quantum well (QW) whose potential depth is controlled by a gate voltage (VG). Quantum transport in the form of negative differential transconductance (NDTC) is observed to temperatures >200 K. The NDTC is tied to a non-monotonic dependence of bipolar current gain on VG that reduces drain-source current through the QW. These devices establish the feasibility of exploiting quantum transport to transform the performance horizons of Si devices fabricated in an industrially scalable manner. Supported by Semiconductor Research Council Task Number 1836.145.

  10. Controlling the Electronic Structures and Properties of in-Plane Transition-Metal Dichalcogenides Quantum Wells

    PubMed Central

    Wei, Wei; Dai, Ying; Niu, Chengwang; Huang, Baibiao

    2015-01-01

    In-plane transition-metal dichalcogenides (TMDs) quantum wells have been studied on the basis of first-principles density functional calculations to reveal how to control the electronic structures and the properties. In collection of quantum confinement, strain and intrinsic electric field, TMD quantum wells offer a diverse of exciting new physics. The band gap can be continuously reduced ascribed to the potential drop over the embedded TMD and the strain substantially affects the band gap nature. The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons. Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials. The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells. In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale. PMID:26616013

  11. Excitons in semiconducting superlattices, quantum wells, and ternary alloys

    SciTech Connect

    Sturge, M.D. . Dept. of Physics); Nahory, R.E.; Tamargo, M.C. )

    1992-06-01

    Semiconducting layered structures can now be fabricated with precisely defined layer thicknesses down to one monolayer. An example is the superlattice'' (SL) structure, in which to semiconductors with different band gaps are interleaved. The electronic and optical properties of the SL are quite different from those of the constitutents and offer interesting new possibilities both in device design and in basic physics. This proposal aims to improve our understanding of optically excited states in SL's, particularly in the so-called Type 2 indirect'' SL's in which in electron and hole created by optical excitation are separated both in real and in momentum space. We study these structures by time-resolved tunable laser spectroscopy, with and without external perturbations such as magnetic field, electric field, and uniaxial stress. In SLs with only a few atomic layers per period the familiar effective mass model'' of semiconductor states breaks down. We have made precise optical experiments on well-characterized material to test current first principles'' calculations of the band structure. Our work under this grant has shown that the material we are using is of sufficiently high quality to test the theoretical predictions. Comparison of theory and experiment provides a new and sensitive probe of the interface quality on a fine scale. Statistical analysis of the temperature dependence of the exciton decay dynamics provides complementary information. From a careful study of the exciton spectra of the recently discovered mixed type 1- type 2 CdTe/CdZnTe SLs we have obtained the band offset at the CdTe/CdZnTe interface to unprecedented accuracy.

  12. Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells

    NASA Astrophysics Data System (ADS)

    Ganichev, S. D.

    gas a charge current, the anomalous Hall effect, can be observed. As both magnetic fields and gyrotropic mechanisms were used authors introduced the notation "magneto-gyrotropic photogalvanic effects" for this class of phenomena. The effect is observed in GaAs and InAs low dimensional structures at free-carrier absorption of terahertz radiation in a wide range of temperatures from liquid helium temperature up to room temperature. The results are well described by the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences unumbiguously that the observed photocurrents are spin-dependent. Microscopic theory of this effect based on asymmetry of photoexcitation and relaxation processes are developed being in a good agreement with experimental data. Note from Publisher: This article contains the abstract only.

  13. Analysis of strain effects on the dynamic spectra of a quantum well semiconductor optical amplifier using quantum well transmission line modelling method

    NASA Astrophysics Data System (ADS)

    Xia, Mingjun; Ghafouri-Shiraz, H.

    2016-04-01

    This paper studies the strain (i.e. compressive (CS) and tensile (TS)) effects on the dynamic spectra of an amplified femtosecond pulse in a quantum well semiconductor optical amplifier (QW-SOA) using quantum well transmission line modelling (QW-TLM) method. Based on the analysis of band structure, the gain spectrum as well as the spontaneous spectrum of quantum well (QW) in the CS, unstrained (US) and TS are investigated using QW-TLM and it was found that in the CS QW, the magnitude ratio of the gain spectrum and the spontaneous emission spectrum is the largest. Furthermore, QW-TLM is adopted to investigate the dynamic spectral evolution of femtosecond pulse amplification in QW-SOAs and it was found that as the femtosecond pulse approaches the amplifier output, the centre frequency of the amplified femtosecond pulse spectra decreases and its bandwidth decreases. The output spectra of the amplified femtosecond pulse in QW amplifiers under the CS, US and TS cases are compared and the simulation results show that in a CS QW-SOA the spectral shape exhibits the largest magnitude and the smallest fluctuation due to the largest gain and the largest ratio between the gain and noise.

  14. Photon drag in single and multiple two-level quantum wells

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Keller, Ole

    1997-06-01

    Starting from a density-matrix operator description we derive an expression for the photon-drag response tensor of a quantum-well system containing an arbitrary number of subbands. Subsequently we analyze the structure of the nonlinear response tensor and make a specialization to the case of a two-level quantum well. In the wake of a self-consistent calculation of the local fields in a two-level well and in multiple quantum wells the photon-drag currents are determined. We illustrate the main ingredients of our theory by carrying out a number of numerical calculations of the drag current in a 15-Å wide niobium quantum well deposited on a crystalline quartz substrate and a GaAs/AlxGa1-xAs multiple-quantum-well structure. In particular we pay attention to the frequency, angle of incidence, and number of wells dependencies of the current, and we demonstrate that local-field effects may give rise to a significant blueshift and an asymmetric form of the resonance peak.

  15. Wavelength sensitive detector based on ICD in two coupled quantum wells

    NASA Astrophysics Data System (ADS)

    Goldzak, Tamar; Gilary, Ido; Moiseyev, Nimrod

    2014-05-01

    We design a wavelength sensitive detector based on inter coulombic decay (ICD) mechanism in a two-quantum well nano-structure. The two coupled quantum wells are designed to satisfy the specific conditions which allow the ICD to occur. In this setup, by absorbing light an electron in one well is excited. Its relaxation back to the ground state is a non-radiative process which transfers the excess energy to the ionization of the electron in the neighboring well into the continuum. Only radiation with a specific wavelength will be absorbed, when the wavelength matches the excitation energy in the quantum well. By applying a weak bias a current is obtained even when light with a very low intensity is absorbed. For the ICD to be dominant decay mechanism it must prevail over all other possible competitive decay processes. We have found that the lifetime of the ICD is on the timescale of picoseconds. Control over the ICD lifetime can be achieved by variation of different parameters in the two quantum well nano-structure. The most useful parameter is the distance between the two quantum wells. We show that as the distance decreases the decay rate of the ICD increases. Furthermore the distance can be tuned such that the emitted electron would be in a metastable state in the continuum (a resonance state); this causes the life time of the ICD to be an order of magnitude smaller, and improves the efficiency of the ICD.

  16. Low-dimensional CdS/CdTe multiple-quantum well heterostructure for optical refrigeration

    NASA Astrophysics Data System (ADS)

    Tarín-Cordero, Julio C.; Villa-Angulo, Rafael; Villa-Angulo, José R.; Villa-Angulo, Carlos

    2015-01-01

    The major challenge for semiconductors to achieve temperatures below 10 K by luminescence upconversion, is that at these lattice temperatures the acoustic phonon component dominates and the scattering rate becomes comparable to the band-to-band radiative transition rate. This problem can be significantly alleviated by employing quantum-confined systems, where relaxation of wave-vector conservation in the confined direction reduces material conductivity by nearly three orders of magnitude. Although previous studies have reported theoretical and experimental analyses of cooling characteristics for bulk semiconductors, the electron band-to-band transition due to photon absorption or photon emission under cooling conditions in quantum-confined semiconductor systems which exhibit quantum effects at the dimensions of several nanometers have not been completely analyzed in conventional theoretical studies. We realized a numerical investigation of optical cooling conditions for a low-dimensional CdS/CdTe multiple-quantum well heterostructure where injected carriers in the active region are quantum mechanically confined in one dimension. Effects of such quantum mechanically confined carriers on photon absorption and photoluminescence (PL) were analyzed under cooling conditions. Most importantly, the CdS/CdTe heterostructure absorption and PL spectra for cooling conditions were defined in terms of the active layer width and number of quantum wells in the complete heterostructure.

  17. Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

    NASA Astrophysics Data System (ADS)

    Lumb, M. P.; Yakes, M. K.; González, M.; Bennett, M. F.; Schmieder, K. J.; Affouda, C. A.; Herrera, M.; Delgado, F. J.; Molina, S. I.; Walters, R. J.

    2016-05-01

    In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm2 to be realized.

  18. Wavelength limits for InGaN quantum wells on GaN

    SciTech Connect

    Pristovsek, Markus

    2013-06-17

    The emission wavelength of coherently strained InGaN quantum wells (QW) is limited by the maximum thickness before relaxation starts. For high indium contents x>40% the resulting wavelength decreases because quantum confinement dominates. For low indium content x<40% the electron hole wave function overlap (and hence radiative emission) is strongly reduced with increasing QW thickness due to the quantum confined Stark effect and imposes another limit. This results in a maximum usable emission wavelength at around 600 nm for QWs with 40%-50% indium content. Relaxed InGaN buffer layers could help to push this further, especially on non- and semi-polar orientations.

  19. In-well pumped mid-infrared PbTe/CdTe quantum well vertical external cavity surface emitting lasers

    SciTech Connect

    Khiar, A. Witzan, M.; Hochreiner, A.; Eibelhuber, M.; Springholz, G.; Volobuev, V.

    2014-06-09

    Optical in-well pumped mid-infrared vertical external cavity surface emitting lasers based on PbTe quantum wells embedded in CdTe barriers are realized. In contrast to the usual ternary barrier materials of lead salt lasers such as PbEuTe of PbSrTe, the combination of narrow-gap PbTe with wide-gap CdTe offers an extremely large carrier confinement, preventing charge carrier leakage from the quantum wells. In addition, optical in-well pumping can be achieved with cost effective and readily available near infrared lasers. Free carrier absorption, which is a strong loss mechanism in the mid-infrared, is strongly reduced due to the insulating property of CdTe. Lasing is observed from 85 K to 300 K covering a wavelength range of 3.3–4.2 μm. The best laser performance is achieved for quantum well thicknesses of 20 nm. At low temperature, the threshold power is around 100 mW{sub P} and the output power more than 700 mW{sub P}. The significance of various charge carrier loss mechanisms are analyzed by modeling the device performance. Although Auger losses are quite low in IV–VI semiconductors, an Auger coefficient of C{sub A} = 3.5 × 10{sup −27} cm{sup 6} s{sup −1} was estimated for the laser structure, which is attributed to the large conduction band offset.

  20. Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition.

    PubMed

    Lee, Wonyoung; Dasgupta, Neil P; Jung, Hee Joon; Lee, Jung-Rok; Sinclair, Robert; Prinz, Fritz B

    2010-12-01

    We report the use of scanning tunneling spectroscopy (STS) to investigate one-dimensional quantum confinement effects in lead sulfide (PbS) thin films. Specifically, quantum confinement effects on the band gap of PbS quantum wells were explored by controlling the PbS film thickness and potential barrier height. PbS quantum well structures with a thickness range of 1-20 nm were fabricated by atomic layer deposition (ALD). Two barrier materials were selected based on barrier height: aluminum oxide as a high barrier material and zinc oxide as a low barrier material. Band gap measurements were carried out by STS, and an effective mass theory was developed to compare the experimental results. Our results show that the band gap of PbS thin films increased as the film thickness decreased, and the barrier height increased from 0.45 to 2.19 eV.

  1. Irreversible temperature quenching and antiquenching of photoluminescence of ZnS/CdS:Mn/ZnS quantum well quantum dots

    NASA Astrophysics Data System (ADS)

    Ding, X.; Dai, R. C.; Zhao, Z.; Wang, Z. P.; Sun, Z. Q.; Zhang, Z. M.; Ding, Z. J.

    2015-04-01

    An experimental observation on irreversible thermal quenching and antiquenching behavior is reported for photoluminescence of ZnS/CdS:Mn/ZnS quantum well quantum dots. The dual-color emissions, a blue emission centered at 430 nm and a Mn2+4T1 → 6A1 orange emission at 600 nm, were found to have different dependences of emission intensity on temperature in the range of 8-290 K. During temperature cooling/heating process, besides the usual thermal quenching, the orange emission shows stronger antiquenching behavior than that of blue emission in a certain temperature range.

  2. Interband optical transition energy and oscillator strength in a lead based CdSe quantum dot quantum well heterostructure

    SciTech Connect

    Saravanamoorthy, S. N.; Peter, A. John

    2015-06-24

    Binding energies of the exciton and the interband optical transition energies are studied in a CdSe/Pb{sub 1-x}Cd{sub x}Se/CdSe spherical quantum dot-quantum well nanostructure taking into account the geometrical confinement effect. The core and shell are taken as the same material. The initial and final states of energy and the overlap integrals of electron and hole wave functions are determined by the oscillator strength. The oscillator strength and the radiative transition life time with the dot radius are investigated for various Cd alloy content in the core and shell materials.

  3. Ultrafast spin tunneling and injection in coupled nanostructures of InGaAs quantum dots and quantum well

    SciTech Connect

    Yang, Xiao-Jie Kiba, Takayuki; Yamamura, Takafumi; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

    2014-01-06

    We investigate the electron-spin injection dynamics via tunneling from an In{sub 0.1}Ga{sub 0.9}As quantum well (QW) to In{sub 0.5}Ga{sub 0.5}As quantum dots (QDs) in coupled QW-QDs nanostructures. These coupled nanostructures demonstrate ultrafast (5 to 20 ps) spin injection into the QDs. The degree of spin polarization up to 45% is obtained in the QDs after the injection, essentially depending on the injection time. The spin injection and conservation are enhanced with thinner barriers due to the stronger electronic coupling between the QW and QDs.

  4. Electronic states of semiconductor-metal-semiconductor quantum-well structures

    NASA Technical Reports Server (NTRS)

    Huberman, M. L.; Maserjian, J.

    1988-01-01

    Quantum-size effects are calculated in thin layered semiconductor-metal-semiconductor structures using an ideal free-electron model for the metal layer. The results suggest new quantum-well structures having device applications. Structures with sufficiently high-quality interfaces should exhibit effects such as negative differential resistance due to tunneling between allowed states. Similarly, optical detection by intersubband absorption may be possible. Ultrathin metal layers are predicted to behave as high-density dopant sheets.

  5. Energy spectrum and transport in narrow HgTe quantum wells

    SciTech Connect

    Germanenko, A. V.; Minkov, G. M.; Rut, O. E.; Sherstobitov, A. A.; Dvoretsky, S. A.; Mikhailov, N. N.

    2015-01-15

    The results of an experimental study of the transport phenomena and the hole energy spectrum of two-dimensional systems in the quantum well of HgTe zero-gap semiconductor with normal arrangement of quantum-confinement subbands are presented. An analysis of the experimental data allows us to reconstruct the carrier energy spectrum near the hole subband extrema. The results are interpreted using the standard kP model.

  6. Strongly confined tunnel-coupled one-dimensional electron systems from an asymmetric double quantum well

    NASA Astrophysics Data System (ADS)

    Buchholz, S. S.; Fischer, S. F.; Kunze, U.; Schuh, D.; Abstreiter, G.

    2008-03-01

    Vertically stacked quantum point contacts (QPCs) are prepared by atomic force microscope (AFM) lithography from an asymmetric GaAs/AlGaAs double quantum well (DQW) heterostructure. Top- and back-gate voltages are used to tune the tunnel-coupled QPCs, and back-gate bias cooling is employed to investigate coupled and decoupled one-dimensional (1D) modes. Parity dependent mode coupling is invoked by the particular asymmetry in the vertical DQW confinement.

  7. Correlation between the structural and cathodoluminescence properties in InGaN/GaN multiple quantum wells with large number of quantum wells

    SciTech Connect

    Yang, Jing; Zhao, Degang Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing; Wang, Hui; Yang, Hui; Jahn, Uwe

    2014-09-01

    Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters.

  8. Modeling of THz Lasers Based on Intersubband Transitions in Semiconductor Quantum Wells

    NASA Technical Reports Server (NTRS)

    Liu, Ansheng; Woo, Alex C. (Technical Monitor)

    1999-01-01

    In semiconductor quantum well structures, the intersubband energy separation can be adjusted to the terahertz (THz) frequency range by changing the well width and material combinations. The electronic and optical properties of these nanostructures can also be controlled by an applied dc electric field. These unique features lead to a large frequency tunability of the quantum well devices. In the on-going project of modeling of the THz lasers, we investigate the possibility of using optical pumping to generate THz radiation based on intersubband transitions in semiconductor quantum wells. We choose the optical pumping because in the electric current injection it is difficult to realize population inversion in the THz frequency range due to the small intersubband separation (4-40 meV). We considered both small conduction band offset (GaAs/AlGaAs) and large band offset (InGaAs/AlAsSb) quantum well structures. For GaAs/AlGaAs quantum wells, mid-infrared C02 lasers are used as pumping sources. For InGaAs/AlAsSb quantum wells, the resonant intersubband transitions can be excited by the near-infrared diode lasers. For three- and four-subband quantum wells, we solve the pumpfield-induced nonequilibrium distribution function for each subband of the quantum well system from a set of rate equations that include both intrasubband and intersubband relaxation processes. Taking into account the coherent interactions between pump and THz (signal) waves, we calculate the optical gain for the THz field. The gain arising from population inversion and stimulated Raman processes is calculated in a unified manner. A graph shows the calculated THz gain spectra for three-subband GaAs/AlGaAs quantum wells. We see that the coherent pump and signal wave interactions contribute significantly to the gain. The pump intensity dependence of the THz gain is also studied. The calculated results are shown. Because of the optical Stark effect and pump-induced population redistribution, the maximum

  9. Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

    NASA Astrophysics Data System (ADS)

    Morrison, C.; Casteleiro, C.; Leadley, D. R.; Myronov, M.

    2016-09-01

    The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.

  10. A gold hybrid structure as optical coupler for quantum well infrared photodetector

    SciTech Connect

    Ding, Jiayi; Li, Qian; Jing, Youliang; Chen, Xiaoshuang Li, Zhifeng; Li, Ning; Lu, Wei

    2014-08-28

    A hybrid structure consisting of a square lattice of gold disk arrays and an overlaying gold film is proposed as an optical coupler for a backside-illuminated quantum well infrared photodetector (QWIP). Finite difference time-domain method is used to numerically simulate the reflection spectra and the field distributions of the hybrid structure combined with the QWIP device. The results show that the electric field component perpendicular to the quantum well is strongly enhanced when the plasmonic resonant wavelength of the hybrid structure coincides with the response one of the quantum well infrared photodetector regardless of the polarization of the incident light. The effect of the diameter and thickness of an individual gold disk on the resonant wavelength is also investigated, which indicates that the localized surface plasmon also plays a role in the light coupling with the hybrid structure. The coupling efficiency can exceed 50 if the structural parameters of the gold disk arrays are well optimized.

  11. Anisotropy of the electron g factor in quantum wells based on cubic semiconductors

    SciTech Connect

    Alekseev, P. S.

    2013-09-15

    A new mechanism for the spin splitting of electron levels in asymmetric quantum wells based on GaAs-type semiconductors relative to rotations of the magnetic field in the well plane is suggested. It is demonstrated that the anisotropy of the Zeeman splitting (linear in a magnetic field) arises in asymmetric quantum wells due to the interface spin-orbit terms in the electron Hamiltonian. In the case of symmetric quantum wells, it is shown that the anisotropy of the Zeeman splitting is a cubic function of the magnitude of the magnetic field, depends on the direction of the magnetic field in the interface plane as the fourth-order harmonic, and is governed by the spin-orbit term of the fourth order by the kinematic momentum in the electron Hamiltonian of a bulk semiconductor.

  12. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping.

    PubMed

    Griffiths, James T; Zhang, Siyuan; Rouet-Leduc, Bertrand; Fu, Wai Yuen; Bao, An; Zhu, Dandan; Wallis, David J; Howkins, Ashley; Boyd, Ian; Stowe, David; Kappers, Menno J; Humphreys, Colin J; Oliver, Rachel A

    2015-11-11

    Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices.

  13. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping.

    PubMed

    Griffiths, James T; Zhang, Siyuan; Rouet-Leduc, Bertrand; Fu, Wai Yuen; Bao, An; Zhu, Dandan; Wallis, David J; Howkins, Ashley; Boyd, Ian; Stowe, David; Kappers, Menno J; Humphreys, Colin J; Oliver, Rachel A

    2015-11-11

    Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices. PMID:26488912

  14. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping

    PubMed Central

    2015-01-01

    Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices. PMID:26488912

  15. Compact triple coupled quantum well system for electrical/optical control of optical bi/multistability.

    PubMed

    Sattari, Hamed; Sahrai, Mostafa; Ebadollahi-Bakhtevar, Solmaz

    2015-03-20

    Optical bistability (OB) and optical multistability (OM) are investigated in a triple coupled quantum wells system inside a semiconductor cavity sandwiched by distributed Bragg reflector mirrors. By proper manipulation of the optical and electrical parameters, the behaviors of OB and OM can be efficiently controlled. We show that, by tuning the tunneling rates between the quantum wells, the threshold and hysteresis cycle of OB and OM can be engineered. The effect of the incoherent pump field as well as the cooperation parameter on creation of OB is also discussed. PMID:25968535

  16. Indium distribution at the interfaces of (Ga,In)(N,As)/GaAs quantum wells

    SciTech Connect

    Luna, E.; Ishikawa, F.; Batista, P. D.; Trampert, A.

    2008-04-07

    The indium distribution across (Ga,In)(N,As) quantum wells is determined by using transmission electron microscopy techniques. Inside the quantum well, the indium distribution is well described by Muraki's segregation model; however, it fails in reflecting the concentration at the interfaces. To describe them, we propose a sigmoidal law which defines the smooth variation of the indium concentration with the position and provides a systematic and quantitative characterization of the interfaces. The thermal stability of the interfaces and their interplay with segregation effects are discussed. A connection between the high thermal robustness of the interfaces and the inherent thermodynamic miscibility gap of the alloy is suggested.

  17. In(x)Ga(1-x)As/GaAs Quantum-Well Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D.; Park, Jin S.; Lin, True-Lon; Liu, John K.

    1995-01-01

    Choice of materials for present quantum-well infrared photodetectors (QWIPs) affected principally by two considerations. One was that in comparison with GaAs, In(x)Ga(1-x)As is potentially superior quantum-well material because of its stronger absorption of infrared radiation. Other consideration was that in comparison with Al(x)Ga(1-x)As, which is usual barrier material in older devices, GaAs potentially superior barrier material because it exhibits superior transport properties (lower scattering and higher mobility of charge carriers). GaAs is well material in older devices and barrier material in present devices.

  18. Phonon-drag thermopower in anisotropic AlAs quantum wells

    SciTech Connect

    Lehmann, Dietmar; Tsaousidou, Margarita; Kubakaddi, Shrishail

    2013-12-04

    In the present work we have developed a generalized theory of phonon-drag thermopower Ŝ{sup g} for a highly anisotropic two-dimensional electron gas. For electrons confined in AlAs quantum wells we calculate Ŝ{sup g} as function of temperature. We show that Ŝ{sup g} exhibits a strong anisotropic behavior depending on valley occupancy which can be tuned by well width and strain. Also a great enhancement of Ŝ{sup g} is observed compared to GaAs quantum wells.

  19. Intraband Raman laser gain in a boron nitride coupled quantum well

    NASA Astrophysics Data System (ADS)

    Moorthy, N. Narayana; Peter, A. John

    2016-05-01

    On-centre impurity related electronic and optical properties are studied in a Boron nitride coupled quantum well. Confined energies for the intraband transition are investigated by studying differential cross section of electron Raman scattering taking into consideration of spatial confinement in a B0.3Ga0.7N/BN coupled quantum well. Raman gain as a function of incident optical pump intensity is computed for constant well width. The enhancement of Raman gain is observed with the application of pump power. The results can be applied for the potential applications for fabricating some optical devices such as optical switches, infrared photo-detectors and electro-optical modulator.

  20. Enhancement of photon intensity in forced coupled quantum wells inside a semiconductor microcavity.

    PubMed

    Eleuch, Hichem; Prasad, Awadhesh; Rotter, Ingrid

    2013-02-01

    We study numerically the photon emission from a semiconductor microcavity containing N≥2 quantum wells under the influence of a periodic external forcing. The emission is determined by the interplay between external forcing and internal interaction between the wells. While the external forcing synchronizes the periodic motion, the internal interaction destroys it. The nonlinear term of the Hamiltonian supports the synchronization. The numerical results show a jump of the photon intensity to very large values at a certain critical value of the external forcing when the number of quantum wells is not too large. We discuss the dynamics of the system across this transition. PMID:23496600

  1. Growth and characterization of SiGeSn quantum well photodiodes.

    PubMed

    Fischer, Inga A; Wendav, Torsten; Augel, Lion; Jitpakdeebodin, Songchai; Oliveira, Filipe; Benedetti, Alessandro; Stefanov, Stefan; Chiussi, Stefano; Capellini, Giovanni; Busch, Kurt; Schulze, Jörg

    2015-09-21

    We report on the fabrication and electro-optical characterization of SiGeSn multi-quantum well PIN diodes. Two types of PIN diodes, in which two and four quantum wells with well and barrier thicknesses of 10 nm each are sandwiched between B- and Sb-doped Ge-regions, were fabricated as single-mesa devices, using a low-temperature fabrication process. We discuss measurements of the diode characteristics, optical responsivity and room-temperature electroluminescence and compare with theoretical predictions from band structure calculations. PMID:26406705

  2. Recombination kinetics of photogenerated electrons in InGaAs/InP quantum wells

    NASA Astrophysics Data System (ADS)

    Tito, M. A.; Pusep, Yu. A.; Gold, A.; Teodoro, M. D.; Marques, G. E.; LaPierre, R. R.

    2016-03-01

    The electron transport and recombination processes of photoexcited electron-hole pairs were studied in InGaAs/InP single quantum wells. Comprehensive transport data analysis reveals a asymmetric shape of the quantum well potential where the electron mobility was found to be dominated by interface-roughness scattering. The low-temperature time-resolved photoluminescence was employed to investigate recombination kinetics of photogenerated electrons. Remarkable modification of Auger recombination was observed with variation of the electron mobility. In high mobility quantum wells, the increasing pump power resulted in a new and unexpected phenomenon: a considerably enhanced Auger non-radiative recombination time. We propose that the distribution of the photoexcited electrons over different conduction band valleys might account for this effect. In low mobility quantum wells, disorder-induced relaxation of the momentum conservation rule causes inter-valley transitions to be insignificant; as a consequence, the non-radiative recombination time is reduced with the increase in pump power. Thus, interface-roughness scattering was found responsible for both transport properties and dynamic optical response in InGaAs/InP quantum wells.

  3. Investigation of Transmission Resonances with Specific Properties in Rectangular Semiconductor Quantum Wells

    ERIC Educational Resources Information Center

    Niketic, Nemanja; Milanovic, Vitomir; Radovanovic, Jelena

    2012-01-01

    In this paper we provide a detailed analysis of the energy position and type of transmission maxima in rectangular quantum wells (QWs), taking into consideration the difference of electron effective masses in the barrier and well layers. Particular attention is given to transmission maxima that are less than unity and the implications of effective…

  4. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry.

    PubMed

    Ma, Eric Yue; Calvo, M Reyes; Wang, Jing; Lian, Biao; Mühlbauer, Mathias; Brüne, Christoph; Cui, Yong-Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; König, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W; Zhang, Shou-Cheng; Goldhaber-Gordon, David; Kelly, Michael A; Shen, Zhi-Xun

    2015-01-01

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

  5. Molecular states in double quantum wells: nanochemistry for metatmaterials with new optical properties

    NASA Astrophysics Data System (ADS)

    Gutierrez, Rafael M.; Castañeda, Arcesio

    2009-08-01

    Quantum mechanics explains the existence and properties of the chemical bond responsible for the formation of molecules from isolated atoms. In this work we study quantum states of Double Quantum Wells, DQW, formed from isolated Single Quantum Wells, SQWs, that can be considered metamaterials. Using the quantum chemistry definition of the covalent bond, we discuss molecular states in DQW as a kind of nanochemistry of metamaterials with new properties, in particular new optical properties. An important particularity of such nanochemistry, is the possible experimental control of the geometrical parameters and effective masses characterizing the semiconductor heterostructures represented by the corresponding DQW. This implies a great potential for new applications of the controlled optical properties of the metamaterials. The use of ab initio methods of intensive numerical calculations permits to obtain macroscopic optical properties of the metamaterials from the fundamental components: the spatial distribution of the atoms and molecules constituting the semiconductor layers. The metamaterial new optical properties emerge from the coexistence of many body processes at atomic and molecular level and complex quantum phenomena such as covalent-like bonds at nanometric dimensions.

  6. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

    DOE PAGES

    Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; et al

    2015-05-26

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy,more » and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.« less

  7. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

    SciTech Connect

    Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; Konig, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W.; Zhang, Shou -Cheng; Goldhaber-Gordon, David; Kelly, Michael A.; Shen, Zhi -Xun

    2015-05-26

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

  8. Quantized states in superconducting quantum wells biased by an external field

    NASA Astrophysics Data System (ADS)

    Shafranjuk, Serhii; Ketterson, John

    2004-03-01

    The interest to quantized states in superconducting quantum wells (SQW) is stimulated by rapid development of qubit devices. The SQW may be formed in different ways. In this report we consider SQW at a minimum of the superconducting order parameter, which happens, e.g, at a normal core of an Abrikosov vortex or in SINIS junctions (S are the superconducting banks, I is an insulating barrier, N is a thin normal metal layer). The Andreev reflection (when an incident electron is reflected as a hole and vice versa) at opposite SN and NS interfaces (or on SIN and NIS interfaces, which have an intermediate transparency) creates quantized states, which are observed in experiments. The quantization condition depends on the sample purity and the quantum well size, which should be comparable to the superconducting coherence length. However, the quantization condition may also be changed when a bias field is applied across the quantum well, and the phase of the superfluid condensate wave function becomes time-dependent. If the time dependence is arbitrary, and the energy is a bad quantum number, then in accordance with a general quantum mechanical rules no quantized states could arise. However, if the behavior is time-homogeneous (e.g., under influence of a dc field, or of an ac field of constant amplitude), the energy is a good quantum number, and the quantized states may exist. In this work we consider the formation of the quantized states in the SINIS junction biased by a dc and ac voltages. The calculations are made using the boundary conditions in the quasiclassical approximation. The quantization conditions are analyzed versus the quantum well size, the electron mean free path, and the external bias field magnitude.

  9. Confined optical-phonon-assisted cyclotron resonance in quantum wells via two-photon absorption process

    NASA Astrophysics Data System (ADS)

    Phuc, Huynh Vinh; Hien, Nguyen Dinh; Dinh, Le; Phong, Tran Cong

    2016-06-01

    The effect of confined phonons on the phonon-assisted cyclotron resonance (PACR) via both one and two photon absorption processes in a quantum well is theoretically studied. We consider cases when electrons are scattered by confined optical phonons described by the Fuchs-Kliewer slab, Ridley's guided, and Huang-Zhu models. The analytical expression of the magneto-optical absorption coefficient (MOAC) is obtained by relating it to the transition probability for the absorption of photons. It predicts resonant peaks caused by transitions between Landau levels and electric subband accompanied by confined phonons emission in the absorption spectrum. The MOAC and the full-width at half-maximum (FWHM) for the intra- and inter-subband transitions are given as functions of the magnetic field, temperature, and quantum well width. In narrow quantum wells, the phonon confinement becomes more important and should be taken into account in studying FWHM.

  10. Gallium arsenide quantum well-based far infrared array radiometric imager

    NASA Technical Reports Server (NTRS)

    Forrest, Kathrine A.; Jhabvala, Murzy D.

    1991-01-01

    We have built an array-based camera (FIRARI) for thermal imaging (lambda = 8 to 12 microns). FIRARI uses a square format 128 by 128 element array of aluminum gallium arsenide quantum well detectors that are indium bump bonded to a high capacity silicon multiplexer. The quantum well detectors offer good responsivity along with high response and noise uniformity, resulting in excellent thermal images without compensation for variation in pixel response. A noise equivalent temperature difference of 0.02 K at a scene temperature of 290 K was achieved with the array operating at 60 K. FIRARI demonstrated that AlGaAS quantum well detector technology can provide large format arrays with performance superior to mercury cadmium telluride at far less cost.

  11. Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials

    NASA Astrophysics Data System (ADS)

    Schulz, K. Marvin; Vu, Hoan; Schwaiger, Stephan; Rottler, Andreas; Korn, Tobias; Sonnenberg, David; Kipp, Tobias; Mendach, Stefan

    2016-08-01

    We experimentally demonstrate the enhancement of the spontaneous emission rate of GaAs quantum wells embedded in rolled-up metamaterials. We fabricate microtubes whose walls consist of alternating Ag and (In)(Al)GaAs layers with incorporated active GaAs quantum-well structures. By variation of the layer thickness ratio of the Ag and (In)(Al)GaAs layers we control the effective permittivity tensor of the metamaterial according to an effective medium approach. Thereby, we can design samples with elliptic or hyperbolic dispersion. Time-resolved low temperature photoluminescence spectroscopy supported by finite-difference time-domain simulations reveal a decrease of the quantum well's spontaneous emission lifetime in our metamaterials as a signature of the crossover from elliptic to hyperbolic dispersion.

  12. Green light emission by InGaN/GaN multiple-quantum-well microdisks

    SciTech Connect

    Hsu, Yu-Chi; Lo, Ikai Shih, Cheng-Hung; Pang, Wen-Yuan; Hu, Chia-Hsuan; Wang, Ying-Chieh; Tsai, Cheng-Da; Chou, Mitch M. C.; Hsu, Gary Z. L.

    2014-03-10

    The high-quality In{sub x}Ga{sub 1−x}N/GaN multiple quantum wells were grown on GaN microdisks with γ-LiAlO{sub 2} substrate by using low-temperature two-step technique of plasma-assisted molecular beam epitaxy. We demonstrated that the hexagonal GaN microdisk can be used as a strain-free substrate to grow the advanced In{sub x}Ga{sub 1−x}N/GaN quantum wells for the optoelectronic applications. We showed that the green light of 566-nm wavelength (2.192 eV) emitted from the In{sub x}Ga{sub 1−x}N/GaN quantum wells was tremendously enhanced in an order of amplitude higher than the UV light of 367-nm wavelength (3.383 eV) from GaN.

  13. Nonlinear terahertz response of HgTe/CdTe quantum wells

    SciTech Connect

    Chen, Qinjun; Sanderson, Matthew; Zhang, Chao

    2015-08-24

    Without breaking the topological order, HgTe/CdTe quantum wells can have two types of bulk band structure: direct gap type (type I) and indirect gap type (type II). We report that the strong nonlinear optical responses exist in both types of bulk states under a moderate electric field in the terahertz regime. Interestingly, for the type II band structure, the third order conductivity changes sign when chemical potentials lies below 10 meV due to the significant response of the hole excitation close to the bottom of conduction band. Negative nonlinear conductivities suggest that HgTe/CdTe quantum wells can find application in the gain medium of a laser for terahertz radiation. The thermal influences on nonlinear optical responses of HgTe/CdTe quantum wells are also studied.

  14. Decomposition in as-grown (Ga,In)(N,As) quantum wells

    SciTech Connect

    Kong, X.; Trampert, A.; Tournie, E.; Ploog, K.H.

    2005-10-24

    We report on the investigation of the local element distribution in as-grown (Ga,In)(N,As) quantum wells with high In and N contents by using low-loss electron energy-loss spectroscopy combined with dark-field transmission electron microscopy. The (Ga,In)(N,As) quantum wells were grown on GaAs(001) substrates at different growth temperatures by molecular-beam epitaxy. Lateral modulations on the nanometer scale were detected with reversal In and N distributions pointing to the existence of regions with a more favorable Ga-N and In-As bond configurations, respectively. These composition fluctuations are the driving force for the morphological instabilities at the interfaces. Lowering the growth temperature of the quantum well results in a more homogeneous element distribution of the quaternary compound. This result is discussed with regard to the influence of the epitaxial strain and cohesive bond energy on the alloy formation during epitaxial growth.

  15. Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials.

    PubMed

    Schulz, K Marvin; Vu, Hoan; Schwaiger, Stephan; Rottler, Andreas; Korn, Tobias; Sonnenberg, David; Kipp, Tobias; Mendach, Stefan

    2016-08-19

    We experimentally demonstrate the enhancement of the spontaneous emission rate of GaAs quantum wells embedded in rolled-up metamaterials. We fabricate microtubes whose walls consist of alternating Ag and (In)(Al)GaAs layers with incorporated active GaAs quantum-well structures. By variation of the layer thickness ratio of the Ag and (In)(Al)GaAs layers we control the effective permittivity tensor of the metamaterial according to an effective medium approach. Thereby, we can design samples with elliptic or hyperbolic dispersion. Time-resolved low temperature photoluminescence spectroscopy supported by finite-difference time-domain simulations reveal a decrease of the quantum well's spontaneous emission lifetime in our metamaterials as a signature of the crossover from elliptic to hyperbolic dispersion.

  16. The electron g factor in AlGaN/GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Li, Ming; Feng, Zhi-Bo.; Fan, Libo; Zhao, Yilong; Han, Hongpei; Feng, Tuanhui

    2016-04-01

    Considering the Rashba and Zeeman effects, the effective Hamiltonian for electrons in AlGaN/GaN quantum wells (QWs) with the magnetic field is obtained, and the effective transverse and longitudinal g-factor (g⊥,//), are derived. The small anisotropy of the g factor in bulk wurtzite materials is clearly shown, while the anisotropy in QWs induced by the quantum confined effect is evident. Moreover, the average g factor (g*) depends greatly on the position of the origin along the growth axis (c axis). With increasing well thickness, both g⊥ and g// increase, and the g-factor anisotropy first decreases and then increases slowly. Results show the g-factor and its anisotropy in III-nitride QWs can be modulated by the well thickness, and they are greatly affected by the internal electric field and the quantum confined effect.

  17. Intersubband Auger recombination and population inversion in quantum-well subbands

    NASA Technical Reports Server (NTRS)

    Borenstain, S.; Katz, J.

    1989-01-01

    The intersubband-Auger-recombination time of electrons under population-inversion conditions in a single quantum well is calculated by taking into account momentum- and energy-conservation rules, and by employing Fermi-Dirac statistics. The screened matrix element of the electron-electron interaction and the overlap integral are calculated for an infinitely deep quantum well. The results are in a good agreement with published experimental data. As a major nonradiative process, the Auger recombination is related to threshold current of infrared lasers based on intersubband transitions in quantum-well structures. The realization of these devices and other limitations to achieving population inversion are discussed. In view of the results, development of these lasers for emission wavelengths corresponding to energies below the LO-phonon energy seems feasible.

  18. Measurement and modeling of ultrafast carrier dynamics and transport in germanium/silicon-germanium quantum wells.

    PubMed

    Claussen, Stephanie A; Tasyurek, Emel; Roth, Jonathan E; Miller, David A B

    2010-12-01

    We measure the intervalley scattering time of electrons in the conduction band of Ge quantum wells from the direct Γ valley to the indirect L valley to be ~185 fs using a pump-probe setup at 1570 nm. We relate this to the width of the exciton peak seen in the absorption spectra of this material, and show that these quantum wells could be used as a fast saturable absorber with a saturation fluence between 0.11 and 0.27 pJ/μm. We also observe field screening by photogenerated carriers in the material on longer timescales. We model this field screening by incorporating carrier escape from the quantum wells, drift across the intrinsic region, and recovery of the applied voltage through diffusive conduction.

  19. Impurity-free quantum well intermixing for large optical cavity high-power laser diode structures

    NASA Astrophysics Data System (ADS)

    Kahraman, Abdullah; Gür, Emre; Aydınlı, Atilla

    2016-08-01

    We report on the correlation of atomic concentration profiles of diffusing species with the blueshift of the quantum well luminescence from both as-grown and impurity free quantum wells intermixed on actual large optical cavity high power laser diode structures. Because it is critical to suppress catastrophic optical mirror damage, sputtered SiO2 and thermally evaporated SrF2 were used both to enhance and suppress quantum well intermixing, respectively, in these (Al)GaAs large optical cavity structures. A luminescence blueshift of 55 nm (130 meV) was obtained for samples with 400 nm thick sputtered SiO2. These layers were used to generate point defects by annealing the samples at 950 °C for 3 min. The ensuing Ga diffusion observed as a shifting front towards the surface at the interface of the GaAs cap and AlGaAs cladding, as well as Al diffusion into the GaAs cap layer, correlates well with the observed luminescence blue shift, as determined by x-ray photoelectron spectroscopy. Although this technique is well-known, the correlation between the photoluminescence peak blue shift and diffusion of Ga and Al during impurity free quantum well intermixing on actual large optical cavity laser diode structures was demonstrated with both x ray photoelectron and photoluminescence spectroscopy, for the first time.

  20. Study on effect of quantum well number on performance characteristics of GaN-based vertical cavity surface emitting laser

    NASA Astrophysics Data System (ADS)

    Zandi Goharrizi, A.; Alahyarizadeh, Gh.; Hassan, Z.; Abu Hassan, H.

    2013-05-01

    The effect of number of quantum wells and quantum well thickness on the optical performance of InGaN vertical cavity surface emitting laser (VCSEL) was numerically investigated using Integrated System Engineering Technical Computer Aided Design (ISE TCAD) simulation program. The simulation results indicated that the output power and differential quantum efficiency of the double quantum well (DQW) laser were increased and threshold current decreased as compared to the single and triplet quantum wells VCSEL. Threshold current enhancement in the single quantum well (SQW) is attributed to the electron carrier leakage increasing from active layers because of the lower optical confinement factor. Simulation results show that in the double quantum well, the optical material gain and electron and hole carrier densities are approximately uniform with respect to the SQW and TQW. Also these results indicated that the electron current density in the DQW is the lowest. In the active region, electrical field decreased for the double quantum well because of the built-in electrical field reduction inside the quantum well. Finally the effect of quantum well thickness in DQW GaN-based VCSEL was investigated and it was observed that DQW VCSEL with 3 nm quantum wells thickness had the optimum threshold current.

  1. Spin splitting of electron states in lattice-mismatched (110)-oriented quantum wells

    NASA Astrophysics Data System (ADS)

    Nestoklon, M. O.; Tarasenko, S. A.; Benchamekh, R.; Voisin, P.

    2016-09-01

    We show that for lattice-mismatched zinc-blende-type (110)-grown quantum wells a significant contribution to the zero-magnetic-field spin splitting of electron subbands comes from strain-induced spin-orbit coupling. Combining the envelope function theory and atomistic tight-binding approach, we calculate spin-orbit splitting constants for realistic quantum wells. It is found that the strain due to lattice mismatch in conventional GaAs/AlGaAs structures may noticeably modify the spin splitting while in InGaAs/GaAs structures it plays a major role and may even change the sign of the spin splitting constant.

  2. Formulation of a self-consistent model for quantum well pin solar cells

    NASA Astrophysics Data System (ADS)

    Ramey, S.; Khoie, R.

    1997-04-01

    A self-consistent numerical simulation model for a pin single-cell solar cell is formulated. The solar cell device consists of a p-AlGaAs region, an intrinsic i-AlGaAs/GaAs region with several quantum wells, and a n-AlGaAs region. Our simulator solves a field-dependent Schrödinger equation self-consistently with Poisson and Drift-Diffusion equations. The emphasis is given to the study of the capture of electrons by the quantum wells, the escape of electrons from the quantum wells, and the absorption and recombination within the quantum wells. We believe this would be the first such comprehensive model ever reported. The field-dependent Schrödinger equation is solved using the transfer matrix method. The eigenfunctions and eigenenergies obtained are used to calculate the escape rate of electrons from the quantum wells, and the non-radiative recombination rates of electrons at the boundaries of the quantum wells. These rates together with the capture rates of electrons by the quantum wells are then used in a self-consistent numerical Poisson-Drift-Diffusion solver. The resulting field profiles are then used in the field-dependent Schrödinger solver, and the iteration process is repeated until convergence is reached. In a p-AlGaAs i-AlGaAs/GaAs n-AlGaAs cell with aluminum mole fraction of 0.3, with one 100 Å-wide 284 meV-deep quantum well, the eigenenergies with zero field are 36meV, 136meV, and 267meV, for the first, second and third subbands, respectively. With an electric field of 50 kV/cm, the eigenenergies are shifted to 58meV, 160meV, and 282meV, respectively. With these eigenenergies, the thermionic escape time of electrons from the GaAs Γ-valley, varies from 220 pS to 90 pS for electric fields ranging from 10 to 50 kV/cm. These preliminary results are in good agreement with those reported by other researchers.

  3. Experimental investigation of spin-orbit coupling in n-type PbTe quantum wells

    SciTech Connect

    Peres, M. L.; Monteiro, H. S.; Castro, S. de; Chitta, V. A.; Oliveira, N. F.; Mengui, U. A.; Rappl, P. H. O.; Abramof, E.; Maude, D. K.

    2014-03-07

    The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δ{sub so}. The values of Δ{sub so} are linearly dependent on the Fermi wave vector (k{sub F}) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.

  4. Nonlinear photonic diode behavior in energy-graded core-shell quantum well semiconductor rod.

    PubMed

    Ko, Suk-Min; Gong, Su-Hyun; Cho, Yong-Hoon

    2014-09-10

    Future technologies require faster data transfer and processing with lower loss. A photonic diode could be an attractive alternative to the present Si-based electronic diode for rapid optical signal processing and communication. Here, we report highly asymmetric photonic diode behavior with low scattering loss, from tapered core-shell quantum well semiconductor rods that were fabricated to have a large gradient in their bandgap energy along their growth direction. Local laser illumination of the core-shell quantum well rods yielded a huge contrast in light output intensities from opposite ends of the rod.

  5. Effects of Detuning on Control of Intersubband Quantum Well Transitions with Chirped Electromagnetic Pulses

    SciTech Connect

    Blekos, Konstantinos; Terzis, Andreas F.; Simserides, Constantinos; Paspalakis, Emmanuel

    2010-11-10

    We study the interaction of a chirped electromagnetic pulse with intersubband transitions of a double semiconductor quantum well. We specifically consider the interaction of the ground and first excited subbands with the electromagnetic field and use the nonlinear density matrix equations for the description of the system dynamics. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed with emphasis given to the effects of the detuning of the central frequency of the electromagnetic field from resonance.

  6. Two-dimensional electron gas in monolayer InN quantum wells

    SciTech Connect

    Pan, Wei; Dimakis, Emmanouil; Wang, George T.; Moustakas, Theodore D.; Tsui, Daniel C.

    2014-11-24

    We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in monolayer InN quantum wells embedded in GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 5×1015 cm-2 and 420 cm2 /Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES.

  7. Twin extra-high photoluminescence in resonant double-period quantum wells.

    PubMed

    Chang, C H; Cheng, Y H; Hsueh, W J

    2014-12-01

    Twin extra high photoluminescence (PL) in resonant quasi-periodic double-period quantum wells (DPQWs) for higher-generation orders is demonstrated. In the DPQW, the number of maxima in the maximum values of the PL intensity is two, which is different from other quasi-periodic quantum wells (QWs) and traditional periodic QWs. The maximum PL intensity in a DPQW is also stronger than that in a periodic QW under the anti-Bragg condition and that in a Fibonacci QW. Although the peaks of the squared electric field for the twin PL are both located near the QWs, their field profiles are distinct. PMID:25490626

  8. Temperature dependent band offsets in PbSe/PbEuSe quantum well heterostructures

    SciTech Connect

    Simma, M.; Bauer, G.; Springholz, G.

    2012-10-22

    The band offsets of PbSe/Pb{sub 1-x}Eu{sub x}Se multi-quantum wells grown by molecular beam epitaxy are determined as a function of temperature and europium content using temperature-modulated differential transmission spectroscopy. The confined quantum well states in the valence and conduction bands are analyzed using a k{center_dot}p model with envelope function approximation. From the fit of the experimental data, the normalized conduction band offset is determined as 0.45{+-}0.15 of the band gap difference, independently of Eu content up to 14% and temperature from 20 to 300 K.

  9. Dipolar polaritons in microcavity-embedded coupled quantum wells in electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Wilkes, J.; Muljarov, E. A.

    2016-09-01

    We present a microscopic calculation of spatially indirect exciton states in semiconductor coupled quantum wells and polaritons formed from their coupling to the optical mode of a microcavity. We include the presence of electric and magnetic fields applied perpendicular to the quantum well plane. Our model predicts the existence of polaritons that are in the strong-coupling regime and at the same time possess a large static dipole moment. We demonstrate, in particular, that a magnetic field can compensate for the reduction in light-matter coupling that occurs when an electric field impresses a dipole moment on the polariton.

  10. Optical lattices of excitons in InGaN/GaN quantum well systems

    SciTech Connect

    Chaldyshev, V. V. Bolshakov, A. S. Zavarin, E. E.; Sakharov, A. V.; Lundin, V. V.; Tsatsulnikov, A. F.; Yagovkina, M. A.

    2015-01-15

    Optical lattices of excitons in periodic systems of InGaN quantum wells with GaN barriers are designed, implemented, and investigated. Due to the collective interaction of quasi-two-dimensional excitons with light and a fairly high binding energy of excitons in GaN, optical Bragg reflection at room temperature is significantly enhanced. To increase the resonance optical response of the system, new structures with two quantum wells in a periodic supercell are designed and implemented. Resonance reflection of 40% at room temperatures for structures with 60 periods is demonstrated.

  11. Two-dimensional electron gas in monolayer InN quantum wells

    DOE PAGES

    Pan, Wei; Dimakis, Emmanouil; Wang, George T.; Moustakas, Theodore D.; Tsui, Daniel C.

    2014-11-24

    We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in monolayer InN quantum wells embedded in GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 5×1015 cm-2 and 420 cm2 /Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES.

  12. Quantum phase-space picture of Bose-Einstein condensates in a double well

    SciTech Connect

    Mahmud, Khan W.; Perry, Heidi; Reinhardt, William P.

    2005-02-01

    We present a quantum phase-space model of the Bose-Einstein condensate (BEC) in a double-well potential. In a quantum two-mode approximation we examine the eigenvectors and eigenvalues and find that the energy correlation diagram indicates a transition from a delocalized to a fragmented regime. Phase-space information is extracted from the stationary quantum states using the Husimi distribution function. We show that the mean-field phase-space characteristics of a nonrigid physical pendulum arises from the exact quantum states, and that only 4-8 particles per well are needed to reach the semiclassical limit. For a driven double-well BEC, we show that the classical chaotic dynamics is manifest in the dynamics of the quantum states. Phase-space analogy also suggests that a {pi} phase-displaced wave packet put on the unstable fixed point on a separatrix bifurcates to create a superposition of two pendulum rotor states--a macroscopic superposition state of BEC. We show that the choice of initial barrier height and ramping, following a {pi} phase imprinting on the condensate, can be used to generate controlled entangled number states with tunable extremity and sharpness.

  13. Carrier dynamics in Ga(NAsP)/Si multi-quantum well heterostructures with varying well thickness

    NASA Astrophysics Data System (ADS)

    Shakfa, M. K.; Woscholski, R.; Gies, S.; Wegele, T.; Wiemer, M.; Ludewig, P.; Jandieri, K.; Baranovskii, S. D.; Stolz, W.; Volz, K.; Heimbrodt, W.; Koch, M.

    2016-05-01

    Time-resolved photoluminescence (TR-PL) measurements have been performed in Ga(NAsP)/(BGa)(AsP) multi-quantum well heterostructures (MQWHs) with different well thicknesses. The studied structures have been pseudomorphically grown on Si substrates by metal organic vapor phase epitaxy (MOVPE) with an N content of about 7%. Experimental results reveal a shortening in the PL decay time with increasing QW thickness, meanwhile, accompanied by a decrease in the PL intensity. We attribute this behavior to an increasing non-radiative recombination rate for broader QWs which arises from an increasing number of defects in the QW material. The emission-energy distribution of the PL decay time is studied at various temperatures. The PL decay time strongly depends on the emission energy at low temperatures and becomes emission-energy-independent close to room temperature. This is discussed in terms of the carrier localization in the studied structures.

  14. Many-Body Effects and Lineshape of Intersubband Transitions in Semiconductor Quantum Wells

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng

    2003-01-01

    Intersubband Transition (ISBT) infrared (IR) absorption and PL in InAs/AlSb were studied for narrow Quantum Wells (QWs). A large redshift was observed (7-10 meV) as temperature increased. A comprehensive many-body theory was developed for ISBTs including contributions of c-c and c-phonon scatterings. Many-body effects were studied systematically for ISBTs. Redshift and linewidth dependence on temperature, as well as spectral features were well explained by theory.

  15. Electro-absorption and electro-refraction in Ge/SiGe coupled quantum wells

    NASA Astrophysics Data System (ADS)

    Frigerio, Jacopo; Vakarin, Vladyslav; Chaisakul, Papichaya; Ballabio, Andrea; Chrastina, Daniel; Le Roux, Xavier; Vivien, Laurent; Isella, Giovanni; Marris-Morini, Delphine

    2016-05-01

    Electro-absorption and electro-refraction in Ge/SiGe coupled quantum wells (CQW) grown on Si have been investigated by means of optical transmission measurements. The separate confinement of electrons and holes in the heterostructure gives rise to an anomalous Quantum Confined Stark Effect (QCSE) that can be exploited to strongly enhance the electro refractive effect with respect to uncoupled quantum wells. A refractive index variation up to 2.3 x 10-3 has been measured at 1.5 V, with an VπLπ of 0.046 V cm. This result is very promising for the realization of an efficient and compact phase modulator based on the Ge/SiGe material system.

  16. Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells

    NASA Astrophysics Data System (ADS)

    Izhnin, Ihor I.; Nesmelov, Sergey N.; Dzyadukh, Stanislav M.; Voitsekhovskii, Alexander V.; Gorn, Dmitry I.; Dvoretsky, Sergey A.; Mikhailov, Nikolaj N.

    2016-02-01

    This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg1 - x Cd x Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg0.35Cd0.65Te/HgTe/Hg0.35Cd0.65Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe.

  17. Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Kolokolov, Kanstantin I.; Ning, Cun-Zheng

    2003-01-01

    Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

  18. Quantum well structures in thin metal films: simple model physics in reality?

    NASA Astrophysics Data System (ADS)

    Milun, M.; Pervan, P.; Woodruff, D. P.

    2002-02-01

    The quantum wells formed by ultra-thin metallic films on appropriate metallic substrates provide a real example of the simple undergraduate physics problem in quantum mechanics of the `particle in a box'. Photoemission provides a direct probe of the energy of the resulting quantized bound states. In this review the relationship of this simple model system to the real metallic quantum well (QW) is explored, including the way that the exact nature of the boundaries can be taken into account in a relative simple way through the `phase accumulation model'. More detailed aspects of the photoemission probe of QW states are also discussed, notably of the physical processes governing the photon energy dependence of the cross sections, of the influence of temperature, and the processes governing the observed peak widths. These aspects are illustrated with the results of experiments and theoretical studies, especially for the model systems Ag on Fe(100), Ag on V(100) and Cu on fcc Co(100).

  19. Smell sensing and visualizing based on multi-quantum wells spatial light modulator

    NASA Astrophysics Data System (ADS)

    Tian, Fengchun; Zhao, Zhenzhen; Jia, Pengfei; Liao, Hailin; Chen, Danyu; Liu, Shouqiong

    2014-09-01

    For the existing drawbacks of traditional detecting methods which use gratings or prisms to detect light intensity distribution at each wavelength of polychromatic light, a novel method based on multi-quantum wells spatial light modulator (MQWs-SLM) has been proposed in this paper. In the proposed method, MQWs-SLM serves as a distribution features detector of the signal light. It is on the basis of quantum-confine Stark effect (QCSE) that the vertical applied voltage can change the absorption features of exciton in multi-quantum wells, and further change the distribution features of the readout polychromatic light of MQWs-SLM. It can be not only an universal detecting method, but also especially recommended to use in the Electronic nose system for features detecting of signal light so as to realize smell sensing and visualizing. The feasibility of the proposed method has been confirmed by mathematical modeling and analysis, simulation experiments and research status analysis.

  20. Dark current in GaAs/AlxGa1-xAs quantum well infrared detectors

    NASA Astrophysics Data System (ADS)

    Nathan, Vaidya

    2013-01-01

    It is not clear whether the tunneling current in QWIPs depends just on the energy corresponding to motion perpendicular to the plane of the quantum well or on the total energy. In order to get a quantitative assessment of the contribution of energy corresponding to motion in the plane of the quantum well to the dark current we use the following approach. We calculate the dark current in GaAs/AlxGa1-x s quantum well infrared detectors for both tunneling dependent only on Ez, and tunneling dependent on the total energy, and compare the results to experimental data. Comparison of theoretical results with experimental data at 40K shows that motion in the plane of the quantum well plays a significant role in determining the tunneling dark current. Corrections are made to Levine's original formula. Variation of the dark current with barrier width and doping density is systematically studied. It is shown that increasing the barrier width and/or decreasing the doping density in the well do not always reduce the dark current.

  1. Investigation of temperature-dependent photoluminescence in multi-quantum wells

    PubMed Central

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-01-01

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells. PMID:26228734

  2. Effect of the quantum well thickness on the performance of InGaN photovoltaic cells

    SciTech Connect

    Redaelli, L.; Mukhtarova, A.; Valdueza-Felip, S.; Ajay, A.; Durand, C.; Eymery, J.; Monroy, E.; Faure-Vincent, J.

    2014-09-29

    We report on the influence of the quantum well thickness on the effective band gap and conversion efficiency of In{sub 0.12}Ga{sub 0.88}N/GaN multiple quantum well solar cells. The band-to-band transition can be redshifted from 395 to 474 nm by increasing the well thickness from 1.3 to 5.4 nm, as demonstrated by cathodoluminescence measurements. However, the redshift of the absorption edge is much less pronounced in absorption: in thicker wells, transitions to higher energy levels dominate. Besides, partial strain relaxation in thicker wells leads to the formation of defects, hence degrading the overall solar cell performance.

  3. Theory and Experiments on Unstable Resonator and Quantum Well Gallium Arsenide/gallium Aluminum Arsenide Lasers

    NASA Astrophysics Data System (ADS)

    Mittelstein, Michael

    Structures of GaAs/GaAlAs lasers and their performance characteristics are investigated experimentally and theoretically. A self-consistent model for the longitudinal gain and intensity distribution in injection lasers is introduced. The model is applied to unstable-resonator semiconductor lasers to evaluate their lateral losses and quantum efficiencies, and an advanced design is presented. Symmetric, unstable -resonator semiconductor lasers are manufactured and a virtual source point inside the laser more than an order of magnitude narrower than the width of the near field is demonstrated. Young's double-slit experiment is adopted for lateral coherence measurements in semiconductor lasers. A high degree of lateral coherence is found, indicating operation of the unstable-resonator lasers in predominantly one mode. In the pulsed measurements on broad-area, single -quantum-well, graded-index wave-guide, separate-confinement -heterostructure lasers, very high quantum efficiencies, very low losses, and very high output powers are observed. The devices are found to exhibit beam divergence narrower than two times the diffraction limit in single-lobed, far-field patterns. Using these single-quantum-well lasers, the "second quantized-state lasing" is found experimentally, and a simple model is developed to explain it. A general model for the gain spectrum and required current density of quantum-well lasers is introduced. The eigenfunctions and eigenvalues of the charge carriers and optical mode of the transverse structure are used to derive the gain spectrum and current density from the Einstein coefficients. The two-dimensional density of states for the charge carriers and the effective width of the optical mode (not the width of the quantum well) are identified as the dominant parameters. The model includes a new heuristic approach to account for the observed smeared onset of subbands, eliminating convolution calculations. Applications of the model for a typical

  4. Simple evaluation of linewidth-enhancement factor in quantum well laser with strain

    NASA Astrophysics Data System (ADS)

    Wartak, Marek S.; Makino, Toshihiko

    1993-05-01

    A simple formula for linewidth-enhancement factor α in quantum well laser with strain was derived and compared with Westbrook and Adams theory [IEE Proc. 135. Pt.J, 223 (1988)]. Strain is incorporated through light and heavy hole effective masses. It has been found that tensile strain results in better improvement of ‖αmat‖ than compressive strain.

  5. Instantaneous amplitude and frequency dynamics of coherent wave mixing in semiconductor quantum wells

    SciTech Connect

    Chemla, D.S.

    1993-06-30

    This article reviews recent investigations of nonlinear optical processes in semiconductors. Section II discusses theory of coherent wave mixing in semiconductors, with emphasis on resonant excitation with only one exciton state. Section III reviews recent experimental investigations of amplitude and phase of coherent wave-mixing resonant with quasi-2d excitons in GaAs quantum wells.

  6. High resolution InSb quantum well ballistic nanosensors for room temperature applications

    SciTech Connect

    Gilbertson, Adam; Cohen, L. F.; Lambert, C. J.; Solin, S. A.

    2013-12-04

    We report the room temperature operation of a quasi-ballistic InSb quantum well Hall sensor that exhibits a high frequency sensitivity of 560nT/√Hz at 20uA bias current. The device utilizes a partitioned buffer layer design that suppresses leakage currents through the mesa floor and can sustain large current densities.

  7. Effect of hydrogenic impurity on the third-harmonic generation in a quantum well

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongmin; Guo, Kangxian; Mou, Sen; Xiao, Bo; Liao, Lei

    2014-12-01

    The third-harmonic generation (THG) coefficients in a quantum well with hydrogenic impurity are theoretically investigated with the compact-density-matrix approach and iterative method. The wave functions and the energy levels can be obtained by using variational method and numerical method. Numerical results show that the THG coefficients are strongly affected by the hydrogenic impurity.

  8. On the cascade capture of electrons at donors in GaAs quantum wells

    SciTech Connect

    Aleshkin, V. Ya.

    2015-09-15

    The impact parameter for the cascade capture of electrons at a charged donor in a GaAs quantum well is calculated. A simple approximate analytical expression for the impact parameter is suggested. The temperature dependence of the impact parameter for the case of electron scattering by the piezoelectric potential of acoustic phonons is determined.

  9. The temporal dynamics of impurity photoconductivity in quantum wells in GaAs

    SciTech Connect

    Aleshkin, V. Ya. E-mail: aleshkin@ipm.sci-nnov.ru

    2015-10-15

    A theory of cascade capture at charged donors in quantum wells (QWs) is developed without using the Fokker-Planck approximation, which is not valid in QWs. The time dependences of impurity photoconductivity and photoelectron concentration in GaAs QWs are determined. The cascade capture time as a function of the charge donor concentration is calculated.

  10. Interaction between Rashba and Zeeman effects in a quantum well channel.

    PubMed

    Choi, Won Young; Kwon, Jae Hyun; Chang, Joonyeon; Han, Suk Hee; Koo, Hyun Cheol

    2014-05-01

    The applied field induced Zeeman effect interferes with Rashba effect in a quantum well system. The angle dependence of Shubnikov-de Haas oscillation shows that the in-plane term of the applied field changes the intrinsic Rashba induced spin splitting. The total effective spin-orbit interaction parameter is determined by the vector sum of the Rashba field and the applied field.

  11. Polarization-entangled mid-infrared photon generation in p-doped semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Razali, R.; Ikonić, Z.; Indjin, D.; Harrison, P.

    2016-11-01

    The optimal design of double quantum well structures for generation of polarization-entangled photons in the mid-infrared range, based on the valence intersubband transitions spontaneous parametric downconversion, is considered. The efficiency and frequency selectivity of the process are also estimated.

  12. Manipulation of nanoscale V-pits to optimize internal quantum efficiency of InGaN multiple quantum wells

    SciTech Connect

    Chang, Chiao-Yun; Li, Heng; Shih, Yang-Ta; Lu, Tien-Chang

    2015-03-02

    We systematically investigated the influence of nanoscale V-pits on the internal quantum efficiency (IQE) of InGaN multiple quantum wells (MQWs) by adjusting the underlying superlattices (SLS). The analysis indicated that high barrier energy of sidewall MQWs on V-pits and long diffusion distance between the threading dislocation (TD) center and V-pit boundary were crucial to effectively passivate the non-radiative centers of TDs. For a larger V-pit, the thicker sidewall MQW on V-pit would decrease the barrier energy. On the contrary, a shorter distance between the TD center and V-pit boundary would be observed in a smaller V-pit, which could increase the carrier capturing capability of TDs. An optimized V-pit size of approximately 200–250 nm in our experiment could be concluded for MQWs with 15 pairs SLS, which exhibited an IQE value of 70%.

  13. Phase Recovery Acceleration of Quantum-Dot Semiconductor Optical Amplifiers by Optical Pumping to Quantum-Well Wetting Layer

    NASA Astrophysics Data System (ADS)

    Kim, Jungho

    2013-11-01

    We theoretically investigate the phase recovery acceleration of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by means of the optical pump injection to the quantum-well (QW) wetting layer (WL). We compare the ultrafast gain and phase recovery responses of QD SOAs in either the electrical or the optical pumping scheme by numerically solving 1088 coupled rate equations. The ultrafast gain recovery responses on the order of sub-picosecond are nearly the same for the two pumping schemes. The ultrafast phase recovery is not significantly accelerated by increasing the electrical current density, but greatly improved by increasing the optical pumping power to the QW WL. Because the phase recovery time of QD SOAs with the optical pumping scheme can be reduced down to several picoseconds, the complete phase recovery can be achieved when consecutive pulse signals with a repetition rate of 100 GHz is injected.

  14. Final Report: Free Standing Quantum Wells, August 15, 1996 - May 31, 1999

    SciTech Connect

    Williams, M.D.; Lee, H.W.H.; Collins, J.

    1999-10-11

    Recent advances in microfabrication techniques in conjunction with the precise growth of layers of single crystalline materials by epitaxial growth techniques allow the creation of new electro-optic microstructures. We have selectively etched compositionally modulated 111-v heterostructures to produce quantum wells (QW's) which are confined on both sides by air or vacuum. The material is patterned so to have the QW's suspended horizontally between vertical support posts. This structure is ideal for probing the local properties of solids, e.g., the interaction of quantum confined states with surface or interface states.

  15. Quantum well infrared photodetector research and development at Jet Propulsion Laboratory

    NASA Astrophysics Data System (ADS)

    Gunapala, S. D.; Bandara, S. V.; Liu, J. K.; Luong, E. M.; Rafol, S. B.; Mumolo, J. M.; Ting, D. Z.; Bock, J. J.; Ressler, M. E.; Werner, M. W.; LeVan, P. D.; Chehayeb, R.; Kukkonen, C. A.; Levy, M.; LeVan, P.; Fauci, M. A.

    2001-06-01

    One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the quantum well infrared photodetector (QWIP). In this paper, we discuss the effect of focal plane array nonuniformity on the performance, optimization of the detector design, material growth and processing that has culminated in realization of large format long-wavelength QWIP cameras, holding forth great promise for many applications in 6-18 μm wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in long-wavelength/very long-wavelength dualband QWIP imaging camera for various applications.

  16. Long-wavelength quantum well infrared photodetector (QWIP) research at Jet Propulsion Laboratory

    NASA Astrophysics Data System (ADS)

    Gunapala, Sarath D.; Liu, John K.; Sundaram, Mani; Bandara, Sumith V.; Shott, C. A.; Hoelter, Theodore R.; Maker, Paul D.; Muller, Richard E.

    1996-06-01

    One of the simplest device realizations of the classic particle-in-a-box problem of basic quantum mechanics is the quantum well infrared photodetector (QWIP). Optimization of the detector design and material growth and processing have culminated in the realization of a 15 micrometer cutoff 128 by 128 focal plane array camera and a camera with large (256 by 256 pixel) focal plane array of QWIPs which can see at 8.5 micrometer, holding forth great promise for a variety of applications in the 6 - 25 micrometer wavelength range. This paper discusses the physics of the QWIP and QWIP technology development at Jet Propulsion Laboratory.

  17. Control of the probe absorption in coupled quantum wells in two dimensions

    NASA Astrophysics Data System (ADS)

    Kang, Chengxian; Ma, Yangcheng; Wang, Zhiping; Yu, Benli

    2016-06-01

    We investigate the probe absorption of a weak probe field in two dimensions (the so-called two-dimensional probe absorption) in an asymmetric two coupled quantum wells. It is found that, due to the joint quantum interference induced by the standing-wave and coherent coupling fields, the probe absorption can be easily controlled via adjusting the system parameters in two dimensions. Most importantly, the pattern of probe absorption can be localized at a particular position and the maximal probability of finding the pattern in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state optoelectronics and quantum information science.

  18. Quantum well infrared photodetector research and development at Jet Propulsion Laboratory

    NASA Astrophysics Data System (ADS)

    Gunapala, Sarath D.; Bandara, Sumith V.; Liu, John K.; Hong, Winn; Luong, Edward M.; Mumolo, Jason M.; McKelvey, M. J.; Sengupta, Deepak K.; Singh, Anjali; Shott, C. A.; Carralejo, R.; Maker, Paul D.; Bock, James J.; Ressler, Michael E.; Werner, Michael W.; Krabach, Timothy N.

    1998-07-01

    One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the Quantum Well Infrared Photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128 X 128 QWIP focal plane array camera, hand-held and palmsize 256 X 256 long-wavelength QWIP cameras and 648 X 480 long-wavelength camera, holding forth great promise for myriad applications in 6 - 25 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in broadband QWIPs, mid-wavelength/long-wavelength dualband QWIPs, long- wavelength/very long-wavelength dualband QWIPs, and high quantum efficiency QWIPs for low background applications in 4 - 26 micrometer wavelength region for NASA and DOD applications.

  19. Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Hao, Xiangying; Li, Jiahua; Lv, Xin-You; Si, Liu-Gang; Yang, Xiaoxue

    2009-10-01

    Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.

  20. A delta-doped quantum well system with additional modulation doping

    PubMed Central

    2011-01-01

    A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor ν = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices. PMID:21711656

  1. Tailoring the spin polarization in Ge/SiGe multiple quantum wells

    SciTech Connect

    Giorgioni, Anna; Pezzoli, Fabio; Gatti, Eleonora; Grilli, Emanuele; Guzzi, Mario; Bottegoni, Federico; Cecchi, Stefano; Ciccacci, Franco; Isella, Giovanni; Trivedi, Dhara; Song, Yang; Li, Pengki; Dery, Hanan

    2013-12-04

    We performed spin-resolved photoluminescence measurements on Ge/SiGe multiple quantum wells with different well thickness and using different exciting power densities. The polarization of the direct emission strongly depends on the relative weight of electrons photoexcited from the light and the heavy hole subbands. The study of the polarization as a function of the exciting power highlights the role of the carrier-carrier interactions in determining spin depolarization.

  2. Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well

    NASA Astrophysics Data System (ADS)

    Huang, H. J.; Liu, B.-H.; Lin, C.-T.; Su, W. S.

    2015-11-01

    The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC), or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt) thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles) is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.

  3. Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well

    SciTech Connect

    Huang, H. J. E-mail: hhjhuangkimo@gmail.com; Liu, B. H.; Lin, C. T.; Su, W. S.

    2015-11-15

    The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC), or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt) thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles) is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.

  4. Threshold characteristics of semiconductor lasers under conditions of violation of electroneutrality in quantum wells

    SciTech Connect

    Sokolova, Z N; Tarasov, I S; Asryan, L V

    2013-05-31

    The threshold characteristics of semiconductor lasers are studied theoretically when the electroneutrality in quantum wells is violated. It is shown that even with the infinitely large threshold concentration of the charge carriers of one sign in the wells, the minimum threshold concentration of the carriers of the opposite sign is nonzero. It is found that in InGaAs/GaAs/AlGaAs heterostructures emitting near the wavelength 1.044 {mu}m, in a wide range of values of the electron concentration in the wells the threshold concentrations of free electrons and holes in the waveguide region are small, the contribution of the recombination current in the waveguide region to the total threshold current is negligible and in the case of a single quantum well, the threshold current density is virtually constant, i.e., the violation of electroneutrality in the InGaAs/GaAs/AlGaAs structures with a single quantum well has almost no effect on the threshold current. In the structures with two or three wells the violation of electroneutrality manifests itself much stronger and can lead to either a decrease or an increase in the threshold current. (semiconductor lasers. physics and technology)

  5. Slow and fast light propagation in a triple quantum well nanostructure

    NASA Astrophysics Data System (ADS)

    Solookinejad, Ghahraman; Panahi, Mohsen; Ahmadi Sangachin, Elnaz; Asadpour, Seyyed Hossein

    2016-02-01

    In this paper, we investigate the absorption and dispersion properties of a weak probe field in a triple quantum well nanostructure by using the incoherent pumping fields. A deep 7.1 nm-thick GaAs well is coupled, on one side, to two shallow 6.8 nm-thick Al0.2Ga0.8As wells by a 2.5 nm-thick Al0.4Ga0.6As barrier. The two shallow wells are separated by a 2.0 nm-thick Al0.4Ga0.8As barrier. Both sides of quantum well contact with 36 nm Al0.4Ga0.6As. Therefore, this type of triple quantum well nanostructure can be used as a suitable medium for studying the effect of spontaneously generated coherence (SGC) and interference between incoherent pumping fields on absorption and dispersion properties of weak probe light. We find that the interferences from spontaneous emission and incoherent pumping processes can change the slope of dispersion and group velocity of the probe light from slow to fast or vice versa. Moreover, it is demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.

  6. Quantum-Carnot engine for particle confined to 2D symmetric potential well

    NASA Astrophysics Data System (ADS)

    Belfaqih, Idrus Husin; Sutantyo, Trengginas Eka Putra; Prayitno, T. B.; Sulaksono, Anto

    2015-09-01

    Carnot model of heat engine is the most efficient cycle consisting of isothermal and adiabatic processes which are reversible. Although ideal gas usually used as a working fluid in the Carnot engine, Bender used quantum particle confined in 1D potential well as a working fluid. In this paper, by following Bender we generalize the situation to 2D symmetric potential well. The efficiency is express as the ratio of the initial length of the system to the final length of the compressed system. The result then is shown that for the same ratio, 2D potential well is more efficient than 1D potential well.

  7. Quantum-Carnot engine for particle confined to 2D symmetric potential well

    SciTech Connect

    Belfaqih, Idrus Husin Sutantyo, Trengginas Eka Putra Prayitno, T. B.; Sulaksono, Anto

    2015-09-30

    Carnot model of heat engine is the most efficient cycle consisting of isothermal and adiabatic processes which are reversible. Although ideal gas usually used as a working fluid in the Carnot engine, Bender used quantum particle confined in 1D potential well as a working fluid. In this paper, by following Bender we generalize the situation to 2D symmetric potential well. The efficiency is express as the ratio of the initial length of the system to the final length of the compressed system. The result then is shown that for the same ratio, 2D potential well is more efficient than 1D potential well.

  8. Characterization and modeling of tensil-strained gallium arsenide/indium aluminum arsenic quantum wells

    NASA Astrophysics Data System (ADS)

    Meng, Qingru

    This dissertation intended to provide a foundation for the development of electroabsorptive quantum well devices based on tensile strained GaAs/InAlAs double quantum well (DQW) structures which, in turn, provide polarization insensitivity in the optical response. The effects of structural parameters and electric field on eigenstates and optical properties were examined experimentally and theoretically. A self-consistent analysis program was developed for this study. Samples used in this work were grown by solid-source MBE. The in-situ calibration of alloy composition and growth rate by reflection high energy electron diffraction (RHEED) was compared with ex-situ characterization techniques including double-crystal X-ray diffractometry (DCXD) and transmission electron microscopy (TEM). Quantum confinement effects, coupling effects, and strain effects on carrier eigenstates and interband transitions were investigated by low temperature photoluminescence (PL) and theoretical analysis. Depending on the amount of tensile strain and quantum confinement, electron-light hole transitions can be brought to the absorption edge, which is desired for achieving polarization independence in quantum well structures. Compared to single quantum well structures, the uniqueness of DQWs lies in the interaction of eigenstates in different wells through a finite potential barrier. Energy band diagrams, eigenstates, and absorption coefficients were examined theoretically as a function of electric field applied perpendicularly to the quantum well layers of tensile strained GaAs/InAlAs DQWs with various doping profiles (n-i-n and p-i-n). Low temperature PL measurements were performed on these samples under various bias conditions. It was shown that as far as polarization independence is concerned, the coupled DQW may provide some advantages over the single well. A self-consistent analysis program for tensile strained GaAs/InAlAs DQWs was developed to deal with the quasi-static condition of

  9. Crossover from negative to positive magnetoresistance in the double quantum well system with different starting disorder.

    PubMed

    Kannan, E S; Karamad, M; Kim, Gil-Ho; Farrer, I; Ritchie, D A

    2010-02-01

    Magnetotransport measurements were performed in two widely separated double quantum well systems with different starting disorders. In the weak magnetic field regime, a crossover from negative to positive magnetoresistance in the longitudinal resistivity was observed in the system with weak disorder when the electron densities in the neighboring wells were significantly unbalanced. The crossover was found to be the result of the exchange-energy-assisted interactions between the electrons occupying the lowest subbands in the neighboring wells. In the case of the system with strong disorder short range scattering dominated the scattering process and no such transition in longitudinal resistivity in the low magnetic field regime was observed. However, at high magnetic fields, sharp peaks were observed in the Hall resistance due to the interaction between the edge states in the quantum Hall regime.

  10. Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.

    PubMed

    Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu

    2014-12-29

    Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 μm tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility.

  11. Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.

    PubMed

    Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu

    2014-12-29

    Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 μm tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility. PMID:25607157

  12. Voltage tunable multiple quantum well distributed feedback filter with an electron beam written Schottky grating

    NASA Astrophysics Data System (ADS)

    Zia, O.; Bhattacharya, P. K.; Singh, J.; Brock, T.

    1994-08-01

    A novel optoelectronic filter voltage-tunable characteristics has been developed and implemented in a multiquantum well waveguide device. By virtue of the quantum-confined Stark effect, the refractive index in quantum wells at the periphery of a guiding region can be given a periodicity in the guiding direction by application of a bias on an electron-beam patterned Schottky grating atop the guide. If the period of the Schottky grating and associated index profile satisfies the Bragg condition, as in a resonant distributed feedback structure, band-reject filtering results. Aftering the bias on the Schottky grating changes the refractive index in the wells, thereby providing tunability of the wavelength at which Bragg diffraction occurs.

  13. Energy-transfer pumping of semiconductor nanocrystals using an epitaxial quantum well

    NASA Astrophysics Data System (ADS)

    Achermann, Marc; Petruska, Melissa A.; Kos, Simon; Smith, Darryl L.; Koleske, Daniel D.; Klimov, Victor I.

    2004-06-01

    As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies-for example, displays, fluorescence tagging, solid-state lighting and lasers. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron-hole pairs (the electron-hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron-hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.

  14. Magneto-quantum-resistance oscillations in tunnel-coupled double quantum wells in tilted magnetic fields: Variable Landau biladders

    SciTech Connect

    Lyo, S.K.; Harff, N.E.; Simmons, J.A.

    1998-07-01

    We present a linear-response theory of magneto-quantum-resistance oscillations of the in-plane resistances R{sub xx} and R{sub yy} in two coupled quasi-two-dimensional electron layers in tilted magnetic fields {bold B}=(B{sub {parallel}},B{sub {perpendicular}}), and explain recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. In this system, the electrons are in the two tunnel-split ground sublevels. The cyclotron masses of the two orbits on the Fermi surface have opposite dependences on the in-plane field B{sub {parallel}}: one increases monotonically, while the other decreases as a function of B{sub {parallel}} in the regime of interest. As a result, the rungs of one Landau ladder sweep up through the Fermi level, while those of the other Landau ladder sweep down when B{sub {parallel}} is increased at a fixed perpendicular field B{sub {perpendicular}}. Ridges are obtained in the three-dimensional plots of both R{sub xx} and R{sub yy} and the density of states versus (B{sub {parallel}},B{sub {perpendicular}}) due to Fermi-level crossing by the rungs of the Landau ladders. Giant peaks are obtained when two ridges intersect each other. The (B{sub {parallel}},B{sub {perpendicular}}) dependence of R{sub xx} as well as theoretical evidence of magnetic breakdown yields good agreement with recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. {copyright} {ital 1998} {ital The American Physical Society}

  15. Indirect observation of single-exciton quantum beats in the time-resolved reflection of a single quantum well

    NASA Astrophysics Data System (ADS)

    Malpuech, G.; Kavokin, A.; Leymarie, J.; Vasson, A.

    1999-12-01

    Oscillations in the time-resolved reflection of a single (In,Ga)/As/GaAs quantum well containing a single exciton resonance have been obtained by a numerical Fourier transform of a complex amplitude reflection coefficient restored from thermally detected optical absorption spectra recorded at 0.35 K. The observation is in excellent agreement with a recent theoretical prediction of beats in time-resolved optical spectra of single QWs (L.C. Andreani, G. Panzarini, A.V. Kavokin, M.R. Vladimirova, Phys. Rev. B 57 (1998) 4670).

  16. Optical and Structural Properties of Zn-Cd-Mn-Se Double Quantum Well Systems

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takashi; Ohmori, Kenta; Kodama, Kazuki; Hishikawa, Masao; Fukasawa, Sakyo; Iwasaki, Fumiaki; Muranaka, Tsutomu; Nabetani, Yoichi

    2011-05-01

    Double quantum well (DQW) structures consisting of a ZnCdSe well and a ZnCdMnSe well separated by a ZnSe barrier are grown with molecular beam epitaxy (MBE). The DQW structures are characterized by using X-ray diffraction measurement and simulation. Thickness of each well layer is designed so that the lowest energy level of ZnCdMnSe well is close to the excited level of the ZnCdSe well. Optical properties of the DQWs are studied with photoluminescence (PL) and reflection spectra in external magnetic fields up to 8 T in the Faraday geometry. Exciton transfer from ZnCdMnSe well to ZnCdSe well is observed in magneto PL with energy selective photoexcitation. Exciton energies in ground and excited states are estimated from PL excitation spectra and reflection spectra.

  17. Interface and photoluminescence characteristics of graphene-(GaN/InGaN)n multiple quantum wells hybrid structure

    NASA Astrophysics Data System (ADS)

    Wang, Liancheng; Liu, Zhiqiang; Zhang, Zi-Hui; Tian, Ying Dong; Yi, Xiaoyan; Wang, Junxi; Li, Jinmin; Wang, Guohong

    2016-04-01

    The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer.

  18. Secondary emission and acoustic-phonon scattering induced by strong magnetic fields in multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Sapega, V. F.; Belitsky, V. I.; Ruf, T.; Fuchs, H. D.; Cardona, M.; Ploog, K.

    1992-12-01

    A strong increase of low-frequency Raman scattering has been observed in GaAs/AlxGa1-xAs multiple quantum wells in magnetic fields up to 14 T. The spectra, consisting of background scattering, folded acoustic phonons, and additional features, show resonant behavior with respect to the laser frequency and the strength of the magnetic field. The broad background, usually related to geminate recombination, has its origin in a continuum of Raman processes with the emission of longitudinal-acoustic phonons where crystal momentum is not conserved. Such processes can become dominant when interface fluctuations allow for resonant scattering in individual quantum wells only. Thus phonons with all possible energies contribute to the background scattering efficiency. The observed folded longitudinal-acoustic phonons are in good agreement with calculated frequencies. Additional features, detected in all samples measured, are attributed to local vibrational modes tied to the gaps at the folded Brillouin-zone center and edge. Other peculiarities observed correspond to modes localized at crossings of the folded longitudinal- and transverse-acoustic branches inside the Brillouin zone. The appearance of these local modes is attributed to fluctuations in the well and barrier thicknesses of the quantum wells.

  19. Finite Momentum Pairing and Spatially Varying Order Parameter in Proximitized HgTe Quantum Wells

    NASA Astrophysics Data System (ADS)

    Yacoby, Amir

    Conventional s-wave superconductivity is understood to arise from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs whose net momentum is zero. Several recent studies have focused on structures where such conventional s-wave superconductors are coupled to systems with an unusual configuration of electronic spin and momentum at the Fermi surface. Under these conditions, the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements and theoretical calculations of several HgTe quantum wells coupled to either aluminum or niobium superconductors and subject to a magnetic field in the plane of the quantum well. By studying the oscillatory response of Josephson interference to the magnitude of the in-plane magnetic field, we find that the induced pairing within the quantum well oscillates between singlet and triplet pairing and is spatially varying. Cooper pairs acquire a tunable momentum that grows with magnetic field strength, directly reflecting the response of the spin-dependent Fermi surfaces to the in-plane magnetic field. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter, as well as a general framework within which to investigate electronic spin texture at the Fermi surface of materials.

  20. Temperature transformations of optical spectra in semiconductor flat heterostructures with quantum wells.

    PubMed

    Kondryuk, D V; Derevyanchuk, A V; Kramar, V M

    2016-04-20

    The results of theoretical study of the temperature dependence of a long-wave range fundamental absorption edge in flat nanoheterostructures with a single quantum well (nanofilms) are adduced. The quantum well is assumed to be rectangular, of finite depth, and with unstrained heterojunctions as the nanofilm surface. Energies of electrons, holes, and excitons have been calculated within the framework of the effective mass model using the Green functions techniques, with account of their interaction with polar optical phonons confined within a quantum well. Numerical calculations are performed for nanofilms β-CdS/β-HgS/β-CdS and Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As. It is shown that interaction with optical phonons causes a long-wave shift of the threshold frequency of the fundamental absorption band and a shift of exciton peaks by hundreds of Å for the first mentioned nanofilm and by dozens of Å for the second one, which is characterized by lower magnitudes of the constants of the electron-phonon coupling. The shift magnitude, as well as the height and half-width of the exciton absorption band, changes when the temperature exceeds 80 and 100 K, respectively.

  1. A versatile phenomenological model for the S-shaped temperature dependence of photoluminescence energy for an accurate determination of the exciton localization energy in bulk and quantum well structures

    NASA Astrophysics Data System (ADS)

    Dixit, V. K.; Porwal, S.; Singh, S. D.; Sharma, T. K.; Ghosh, Sandip; Oak, S. M.

    2014-02-01

    Temperature dependence of the photoluminescence (PL) peak energy of bulk and quantum well (QW) structures is studied by using a new phenomenological model for including the effect of localized states. In general an anomalous S-shaped temperature dependence of the PL peak energy is observed for many materials which is usually associated with the localization of excitons in band-tail states that are formed due to potential fluctuations. Under such conditions, the conventional models of Varshni, Viña and Passler fail to replicate the S-shaped temperature dependence of the PL peak energy and provide inconsistent and unrealistic values of the fitting parameters. The proposed formalism persuasively reproduces the S-shaped temperature dependence of the PL peak energy and provides an accurate determination of the exciton localization energy in bulk and QW structures along with the appropriate values of material parameters. An example of a strained InAs0.38P0.62/InP QW is presented by performing detailed temperature and excitation intensity dependent PL measurements and subsequent in-depth analysis using the proposed model. Versatility of the new formalism is tested on a few other semiconductor materials, e.g. GaN, nanotextured GaN, AlGaN and InGaN, which are known to have a significant contribution from the localized states. A quantitative evaluation of the fractional contribution of the localized states is essential for understanding the temperature dependence of the PL peak energy of bulk and QW well structures having a large contribution of the band-tail states.

  2. Well-width dependence of the emission linewidth in ZnO/MgZnO quantum wells

    PubMed Central

    2012-01-01

    Photoluminescence (PL) spectra were measured as a function of well width (LW) and temperature in ZnO/Mg0.1Zn0.9O single quantum wells (QWs) with graded thickness. The emission linewidth (full width at half maximum) was extracted from the emission spectra, and its variation as a function of LW was studied. The inhomogeneous linewidth obtained at 5 K was found to decrease with increasing LW from 1.8 to 3.3 nm due to the reduced potential variation caused by the LW fluctuation. Above 3.3 nm, however, the linewidth became larger with increasing LW, which was explained by the effect related with defect generation due to strain relaxation and exciton expansion in the QW. For the homogenous linewidth broadening, longitudinal optical (LO) phonon scattering and impurity scattering were taken into account. The LO phonon scattering coefficient ΓLO and impurity scattering coefficient Γimp were deduced from the temperature dependence of the linewidth of the PL spectra. Evident reduction of ΓLO with decreasing LW was observed, which was ascribed to the confinement-induced enhancement of the exciton binding energy. Different from ΓLO, a monotonic increase in Γimp was observed with decreasing LW, which was attributed to the enhanced penetration of the exciton wave function into the barrier layers. PMID:23111026

  3. Quantum Hall Ferromagnet in a Double Well with Vanishing g-FACTOR

    NASA Astrophysics Data System (ADS)

    Armas, L. E. G.; Gusev, G. M.; Lamas, T. E.; Bakarov, A. K.; Portal, J. C.

    We have studied the quantum Hall effect in AlxGa1-xAs-double well structure with vanishing g-factor. We determined the density-magnetic field ns - B diagrams for the longitudinal resistance Rxx. In spite of the fact that the ns - B diagram for conventional GaAs double wells shows a striking similarity with the theory, we observed the strong difference between these diagrams for double wells with vanishing g-factor. We argue that the electron-electron interaction is responsible for unusual behavior of the Landau levels in such a system.

  4. Optical-phonon-mediated photocurrent in terahertz quantum-well photodetectors

    SciTech Connect

    Gu, L. L.; Guo, X. G. Fu, Z. L.; Wan, W. J.; Zhang, R.; Tan, Z. Y.; Cao, J. C.

    2015-03-16

    Strong and sharp photocurrent peak at longitudinal optical (LO) phonon frequency (8.87 THz) is found in GaAs/(Al,Ga)As terahertz quantum-well photodetectors (QWPs). Two mesa-structure terahertz QWPs with and without one-dimensional metal grating are fabricated to investigate the behavior of such photoresponse peak. The experimental and simulation results indicate that the photocurrent peak originates from a two-step process. First, at the LO phonon frequency, a large number of non-equilibrium LO phonons are excited by the incident electromagnetic field, and the electromagnetic energy is localized and enhanced in the thin multi-quantum-well layer. Second, through the Frohlich interaction, the localized electrons are excited to continuum states by absorbing the non-equilibrium LO phonons, which leads to the strong photoresponse peak. This finding is useful for exploring strong light-matter interaction and realizing high sensitive terahertz photodetectors.

  5. Dynamics of the energy relaxation in a parabolic quantum well laser

    NASA Astrophysics Data System (ADS)

    Trifonov, A. V.; Cherotchenko, E. D.; Carthy, J. L.; Ignatiev, I. V.; Tzimis, A.; Tsintzos, S.; Hatzopoulos, Z.; Savvidis, P. G.; Kavokin, A. V.

    2016-03-01

    We explore two parabolic quantum well (PQW) samples, with and without Bragg mirrors, in order to optimize the building blocks of a bosonic cascade laser. The photoluminescence spectra of a PQW microcavity sample is compared against that of a conventional microcavity with embedded quantum wells (QWs) to demonstrate that the weak coupling lasing in a PQW sample can be achieved. The relaxation dynamics in a conventional QW microcavity and in the PQW microcavity was studied by a nonresonant pump-pump excitation method. Strong difference in the relaxation characteristics between the two samples was found. The semiclassical Boltzmann equations were adapted to reproduce the evolution of excitonic populations within the PQW as a function of the pump power and the output intensity evolution as a function of the pump-pump pulse delay. Fitting the PQW data confirms the anticipated cascade relaxation, paving the way for such a system to produce terahertz radiation.

  6. Mid/far-infrared photo-detectors based on graphene asymmetric quantum wells

    NASA Astrophysics Data System (ADS)

    Ben Salem, E.; Chaabani, R.; Jaziri, S.

    2016-09-01

    We conducted a theoretical study on the electronic properties of a single-layer graphene asymmetric quantum well. Quantification of energy levels is limited by electron–hole conversion at the barrier interfaces and free-electron continuum. Electron–hole conversion at the barrier interfaces can be controlled by introducing an asymmetry between barriers and taking into account the effect of the interactions of the graphene sheet with the substrate. The interaction with the substrate induces an effective mass to carriers, allowing observation of Fabry–Pérot resonances under normal incidence and extinction of Klein tunneling. The asymmetry, between barriers creates a transmission gap between confined states and free-electron continuum, allowing the large graphene asymmetric quantum well to be exploited as a photo-detector operating at mid- and far-infrared frequency regimes.

  7. Bound states in optical absorption of semiconductor quantum wells containing a two-dimensional electron Gas

    PubMed

    Huard; Cox; Saminadayar; Arnoult; Tatarenko

    2000-01-01

    The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.

  8. Terahertz meta-atoms coupled to a quantum well intersubband transition.

    PubMed

    Dietze, D; Benz, A; Strasser, G; Unterrainer, K; Darmo, J

    2011-07-01

    We present a method of coupling free-space terahertz radiation to intersubband transitions in semiconductor quantum wells using an array of meta-atoms. Owing to the resonant nature of the interaction between metamaterial and incident light and the field enhancement in the vicinity of the metal structure, the coupling efficiency of this method is very high and the energy conversion ratio from in-plane to z field reaches values on the order of 50%. To identify the role of different aspects of this coupling, we have used a custom-made finite-difference time-domain code. The simulation results are supplemented by transmission measurements on modulation-doped GaAs/AlGaAs parabolic quantum wells which demonstrate efficient strong light-matter coupling between meta-atoms and intersubband transitions for normal incident electromagnetic waves.

  9. Mid/far-infrared photo-detectors based on graphene asymmetric quantum wells

    NASA Astrophysics Data System (ADS)

    Ben Salem, E.; Chaabani, R.; Jaziri, S.

    2016-09-01

    We conducted a theoretical study on the electronic properties of a single-layer graphene asymmetric quantum well. Quantification of energy levels is limited by electron-hole conversion at the barrier interfaces and free-electron continuum. Electron-hole conversion at the barrier interfaces can be controlled by introducing an asymmetry between barriers and taking into account the effect of the interactions of the graphene sheet with the substrate. The interaction with the substrate induces an effective mass to carriers, allowing observation of Fabry-Pérot resonances under normal incidence and extinction of Klein tunneling. The asymmetry, between barriers creates a transmission gap between confined states and free-electron continuum, allowing the large graphene asymmetric quantum well to be exploited as a photo-detector operating at mid- and far-infrared frequency regimes.

  10. Artificial Graphene in Nano-patterned GaAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Wang, Sheng; Scarabelli, Diego; Kuznetsova, Yuliya Y.; Pfeiffer, Loren N.; West, Ken; Gardner, Geoff C.; Manfra, Michael J.; Pellegrini, Vittorio; Wind, Shalom J.; Pinczuk, Aron

    We report the realization of artificial graphene (AG) in a 2D electron gas in a highly tunable semiconductor quantum well system. Very short period (as small as 40 nm) honeycomb lattices were formed in a GaAs heterostructure by electron beam lithography followed by dry etching. Characterization of the AG samples by photoluminescence at low temperature (about 4K) indicates modulation of 2D electron states. Low-lying electron excitations observed by resonant inelastic light scattering and interpreted with a calculated AG band structure confirm the formation of AG bands with a well-defined Dirac cone, evidence for the presence of massless Dirac fermions. These results suggest that engineered semiconductor nano-scale structures can serve as advanced quantum simulators for probing novel electron behavior in low dimensional systems. Supported by DOE-BES Award DE-SC0010695.

  11. Tunneling spectroscopy of hole plasmons in a valence-band quantum well

    SciTech Connect

    Neves, B.R.; Foster, T.J.; Eaves, L.; Main, P.C.; Henini, M.; Fisher, D.J.; Lerch, M.L.; Martin, A.D.; Zhang, C.

    1996-10-01

    We investigate the current-voltage characteristics of a {ital p}-doped resonant tunneling diode. In the voltage range slightly above the bias corresponding to resonant tunneling of holes into the first light-hole subband of the quantum well, we observe two satellite peaks which we attribute to plasmon-assisted tunneling transitions. A theoretical model is presented to account for these peaks. The model is based on the excitation of intrasubband and intersubband heavy-hole plasmons in the quantum well by hot holes injected close to the energy of the first light-hole subband. We also study the behavior of the satellites when a magnetic field is applied either parallel to or perpendicular to the current. {copyright} {ital 1996 The American Physical Society.}

  12. Heterointerface effects on the nonlinear optical rectification in a laser-dressed graded quantum well

    NASA Astrophysics Data System (ADS)

    Niculescu, Ecaterina C.; Eseanu, Nicoleta; Radu, Adrian

    2013-05-01

    An investigation of the laser radiation effects on the nonlinear optical rectification in an AlGaAs inverse parabolic quantum well with asymmetrical barriers is performed within the effective mass approximation, taking into account the dielectric mismatch between the semiconductor and the surrounding medium. Using the accurate dressing effect for the confinement potential and electrostatic self-energy due to the image-charges, we prove that: (i) a spatially dependent effective mass in the laser-dressing parameter definition is required for precise calculations of the energy levels; (ii) the dielectric confinement provides a potential mechanism for controlling electronic states and optical properties of quantum wells. In addition, the laser dependence of the energy where the optical rectification reaches its maximum can be adjusted by external electric fields. The joint action of the intense high-frequency laser and static electric fields may provide tuning of the nonlinear properties in this type of dielectrically modulated heterostructures.

  13. Room-Temperature Transport of Indirect Excitons in (Al ,Ga )N /GaN Quantum Wells

    NASA Astrophysics Data System (ADS)

    Fedichkin, F.; Guillet, T.; Valvin, P.; Jouault, B.; Brimont, C.; Bretagnon, T.; Lahourcade, L.; Grandjean, N.; Lefebvre, P.; Vladimirova, M.

    2016-07-01

    We report on the exciton propagation in polar (Al ,Ga )N /GaN quantum wells over several micrometers and up to room temperature. The key ingredient to achieve this result is the crystalline quality of GaN quantum wells grown on GaN substrate that limits nonradiative recombination. From the comparison of the spatial and temporal dynamics of photoluminescence, we conclude that the propagation of excitons under continuous-wave excitation is assisted by efficient screening of the in-plane disorder. Modeling within drift-diffusion formalism corroborates this conclusion and suggests that exciton propagation is still limited by the exciton scattering on defects rather than by exciton-exciton scattering so that improving interface quality can boost exciton transport further. Our results pave the way towards room-temperature excitonic devices based on gate-controlled exciton transport in wide-band-gap polar heterostructures.

  14. Magnetospectroscopy of symmetric and anti-symmetric states in double quantum wells

    NASA Astrophysics Data System (ADS)

    Marchewka, M.; Sheregii, E. M.; Tralle, I.; Ploch, D.; Tomaka, G.; Furdak, M.; Kolek, A.; Stadler, A.; Mleczko, K.; Zak, D.; Strupinski, W.; Jasik, A.; Jakiela, R.

    2008-02-01

    The experimental results obtained for magnetotransport in the InGaAs/InAlAs double quantum well (DQW) structures of two different shapes of wells are reported. A beating effect occurring in the Shubnikov-de Haas (SdH) oscillations was observed for both types of structures at low temperatures in the parallel transport when the magnetic field was perpendicular to the layers. An approach for the calculation of the Landau level energies for DQW structures was developed and then applied to the analysis and interpretation of the experimental data related to the beating effect. We also argue that in order to account for the observed magnetotransport phenomena (SdH and integer quantum Hall effect), one should introduce two different quasi-Fermi levels characterizing two electron subsystems regarding the symmetry properties of their states, symmetric and anti-symmetric ones, which are not mixed by electron-electron interaction.

  15. Spin blocking effect in symmetric double quantum well due to Rashba spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Souma, Satofumi; Ogawa, Matsuto; Sekine, Yoshiaki; Sawada, Atsushi; Koga, Takaaki

    2013-03-01

    We report a theoretical study of the spin-dependent electronic current flowing laterally through the In0.53Ga0.47As/In0.52Al0.48As double quantum well (DQW) structure, where the values of the Rashba spin-orbit parameter αR are opposite in sign but equal in magnitude between the constituent quantum wells. By tuning the channel length of DQW and the magnitude of the externally applied in-plane magnetic field, one can block the transmission of one spin (e.g., spin-up) component, enabling us to obtain a spin-polarized current. Our experimental progress toward realizing the proposed device is also reported. This work was supported by JSPS KAKENHI Grant Number 23360001 and 22104007

  16. Synthesis, optical and structural properties of quantum-wells crystals grown into porous alumina

    NASA Astrophysics Data System (ADS)

    Zaghdoudi, W.; Dammak, T.; ElHouichet, H.; Chtourou, R.

    2014-07-01

    In this work, we present the confinement effect of the incorporation of perovskite compounds (C12H25-NH3)2PbI4 quantum wells into different porous anodic aluminum oxide (PAA) matrix via a chemical route. The detailed structure and optical property of the quantum wells in PAA were characterized by FT-IR, UV-Vis absorption and photoluminescence (PL) spectroscopy. The surface topography for the two used PAA matrix has been studied using atomic force microscopy (AFM). The pores diameters (pores spacing) for the two matrix are 15 (35 nm) and 45 (82 nm). UV-visible and photoluminescence spectroscopy of (C12H25-NH3)2PbI4/PAA exhibits a clear blue shift of the fundamental excitonic transition. This effect is attributed to the confinement of the exciton mode in the pore of the PAA matrix.

  17. Improvement of the quantum confined Stark effect characteristics by means of energy band profile modulation: The case of Gaussian quantum wells

    NASA Astrophysics Data System (ADS)

    Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I.

    2011-11-01

    We study the quantum confined stark effect (QCSE) characteristics in Gaussian quantum wells (GQW). This special energy band profile is built varying the aluminum concentration of the AlGaAs ternary alloy in Gaussian fashion. The semi-empirical sp3s* tight-binding model including spin is used to obtain the energy Stark shifts (ESS) and the wave-function Gaussian spatial overlap (GSO) between electrons and holes for different electric field strengths, quantum well widths and aluminum concentrations. We find that both the ESS and the GSO depend parabolically with respect to the electric field strength and the quantum well width. These QCSE characteristics show an asymmetry for the electric field in the forward and reverse directions, related directly to the different band-offset of electrons and holes, being the negative electric fields (reverse direction) more suitable to reach greater ESS. Two important features are presented by this special energy band profile: (1) reductions of the ESS and (2) enhancements of the GSO of tents to hundreds with respect to parabolic and rectangular quantum wells. Even more, tailoring the quantum well width it is possible to reach GSO of thousands with respect to rectangular quantum wells. Finally, it is important to mention that similar results could be obtained in other quantum well heterostructures of materials such as nitrides, oxides (ZnO), and SiGe whenever the confinement band profiles are modulated in Gaussian form.

  18. Dual Band Deep Ultraviolet AlGaN Photodetectors

    NASA Technical Reports Server (NTRS)

    Aslam, S.; Miko, L.; Stahle, C.; Franz, D.; Pugel, D.; Guan, B.; Zhang, J. P.; Gaska, R.

    2007-01-01

    We report on the design, fabrication and characterization of a back-illuminated voltage bias selectable dual-band AlGaN UV photodetector. The photodetector can separate UVA and W-B band radiation by bias switching a two terminal n-p-n homojunction structure that is fabricated in the same pixel. When a forward bias is applied between the top and bottom electrodes, the detector can sense UV-A and reject W-B band radiation. Alternatively, under reverse bias, the photodetector can sense UV-B and reject UV-A band radiation.

  19. High-Power AlGaAs Quantum-Well Lasers On Si Substrates

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Hoon; Lang, Robert J.; Radhakrishnan, Gouri; Katz, Joseph

    1991-01-01

    AlxGa1-xAs lasers of graded-index-of-refraction, separate-confinement-heterostructure, single-quantum-well type fabricated on silicon substrates by migration-enhanced molecular-beam epitaxy followed by metalorganic vapor-phase epitaxy. They are intermediate products of continuing effort to develop low-threshold-current, high-efficiency lasers for parallel optical interconnections between large-scale optoelectronic integrated circuits.

  20. Interaction between Rashba and Zeeman effects in a quantum well channel.

    PubMed

    Choi, Won Young; Kwon, Jae Hyun; Chang, Joonyeon; Han, Suk Hee; Koo, Hyun Cheol

    2014-05-01

    The applied field induced Zeeman effect interferes with Rashba effect in a quantum well system. The angle dependence of Shubnikov-de Haas oscillation shows that the in-plane term of the applied field changes the intrinsic Rashba induced spin splitting. The total effective spin-orbit interaction parameter is determined by the vector sum of the Rashba field and the applied field. PMID:24734592

  1. Infrared studies of induced superconductivity in indium-arsenide quantum wells

    NASA Astrophysics Data System (ADS)

    Eckhause, Tobias Andrew

    The describe experiments which probe the electrical and infrared optical properties of superconductor-semiconductor hybrid structures, specifically structures where superconducting Nb contacts the two-dimensional electron gas in an InAs quantum well. In order to study the supercurrent-carrying Andreev states in a Josephson junction, we conduct transport, experiments in Josephson field-effect transistors, where a voltage applied to an insulated gate modulates the density of electrons in and the supercurrent through an InAs-based weak link. The density-dependence of the critical current fits a model for the Andreev states in the junction in which quasiparticles travel ballistically across the quantum well between superconducting electrodes. Probing the dynamics of these states on the scale of the superconducting energy gap in Nb, we find robust signatures of the proximity effect in the InAs using far-infrared transmission spectroscopy. A model for the conductivity of superconducting thin films predicts transmission spectra which show similarities to the transmission spectra measured in our structures. From this fit we extract an effective energy gap in the InAs quantum well due to the proximity of superconducting Nb. We probe these structures in both superconductor/normal metal geometries---where the superconducting Nb lies directly on top of a layer of InAs---and superconductor/normal metal/superconductor geometries---where the an InAs quantum well connects superconducting Nb stripes. In both geometries we observe proximity effects in the far-infrared transmission spectra of the InAs.

  2. Generalized purity and quantum phase transition for Bose-Einstein condensates in a symmetric double well

    SciTech Connect

    Viscondi, T. F.; Furuya, K.; Oliveira, M. C. de

    2009-07-15

    The generalized purity is employed for investigating the process of coherence loss and delocalization of the Q function in the Bloch sphere of a two-mode Bose-Einstein condensate in a symmetrical double well with cross collision. Quantum phase transition of the model is signaled by the generalized purity as a function of an appropriate parameter of the Hamiltonian and the number of particles (N). A power-law dependence of the critical parameter with N is derived.

  3. Resonant enhancement of the photocurrent in multiple-quantum-well photovoltaic devices

    SciTech Connect

    Raisky, O.Y.; Wang, W.B.; Alfano, R.R.; Reynolds, C.L. Jr.; Stampone, D.V.; Focht, M.W.

    1999-01-01

    Sequential resonant tunneling is proposed to enhance the photocurrent and reduce recombination losses in photovoltaic devices based on multiple-quantum-well (MQW) heterostructures. An InGaAsP/InP MQW {ital p{endash}i{endash}n} diode with built-in sequential resonant tunneling has been fabricated, and demonstrates an increase in the photocurrent and reduction in photoluminescence intensity. These effects are attributed to the resonance tunneling effect. {copyright} {ital 1999 American Institute of Physics.}

  4. Guided-wave photodiode using through-absorber quantum-well-intermixing and methods thereof

    DOEpatents

    Skogen, Erik J.

    2016-10-25

    The present invention includes a high-speed, high-saturation power detector (e.g., a photodiode) compatible with a relatively simple monolithic integration process. In particular embodiments, the photodiode includes an intrinsic bulk absorption region, which is grown above a main waveguide core including a number of quantum wells (QWs) that are used as the active region of a phase modulator. The invention also includes methods of fabricating integrated photodiode and waveguide assemblies using a monolithic, simplified process.

  5. Closed form solution for a double quantum well using Gröbner basis

    NASA Astrophysics Data System (ADS)

    Acus, A.; Dargys, A.

    2011-07-01

    Analytical expressions for the spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and the effective masses are different. This was achieved by using a Gröbner basis algorithm that allowed us to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.

  6. Asymmetric effects on the optical properties of double-quantum well systems

    NASA Astrophysics Data System (ADS)

    Silotia, Poonam; Batra, Kriti; Prasad, Vinod

    2014-02-01

    Linear, nonlinear, and total absorption coefficient and refractive index changes of double-quantum well (DQW) systems are studied theoretically in the presence of external static electric field applied along the growth direction. The analytical expression for the linear and nonlinear optical properties is obtained using density matrix method. Emphasis is laid on the effect of asymmetry in the shapes of DQW system on optical properties. Some interesting results are obtained and explained.

  7. Tunable terahertz detection based on a grating-gated double-quantum-well FET

    NASA Astrophysics Data System (ADS)

    Popov, V. V.; Teperik, T. V.; Tsymbalov, G. M.; Peralta, X. G.; Allen, S. J.; Horing, N. J. M.; Wanke, M. C.

    2004-04-01

    We model resonant terahertz photoconductance recently observed in field-effect transistors with a double-quantum-well (DQW) channel. Comparison of the measured THz resonant photoresponse to the calculated THz absorption spectrum establishes that the resonances are determined by standing plasma waves in the DQW channel under metallic portions of the grating gate. It is found theoretically that the DQW asymmetry mixes the acoustic and optical plasmons resulting in a rather intense ac electric field between the QWs.

  8. A 980 nm pseudomorphic single quantum well laser for pumping erbium-doped optical fiber amplifiers

    NASA Technical Reports Server (NTRS)

    Larsson, A.; Forouhar, S.; Cody, J.; Lang, R. J.; Andrekson, P. A.

    1990-01-01

    The authors have fabricated ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs GRIN-SCH SQW (graded-index separate-confinement-heterostructure single-quantum-well) lasers, emitting at 980 nm, with a maximum output power of 240 mW from one facet and a 22 percent coupling efficiency into a 1.55-micron single-mode optical fiber. These lasers satisfy the requirements on efficient and compact pump sources for Er3+-doped fiber amplifiers.

  9. Inter-dot Effects in a Chain of CdS/CdSe/CdS Quantum Well Quantum Dots

    NASA Astrophysics Data System (ADS)

    Pingenot, Joseph; Mullen, Kieran J.

    2010-03-01

    Although individual quantum well quantum dots (QWQD)s have been studied extensively, regular arrays of QWQDs have not received as much attention. Previous theoretical work on single electrons in a regular array of rings has shown antiferroelectric electron ordering, indicating the possibility of creating systems with antiferroelectric ordering in systems such as QWQDs. We have studied theoretically a chain of identical CdS/CdSe/CdS QWQDs with well thicknesses between 42nm and 10nm, with an external barrier width of 14nm. QWQD cores were between 14nm and 38nm, respectively. Valence and conduction states were calculated for a single QWQD using 8-band k-dot-p theory on a realspace grid using a program developed by Pryor[2]. The potential from the two nearest neighbors was found from the conduction state. For electron-hole interactions, the uppermost valence state of all 3 QWQDs were included. The holes were much more localized than the electrons, causing a large potential around them. A nonsimple potential arises from the combined states. The states were sensitive to the roughness of the sphere. [1]PRB 78 075411 [2] PRB 72 205311

  10. Theory of electron g-tensor in bulk and quantum-well semiconductors

    NASA Astrophysics Data System (ADS)

    Lau, Wayne H.; Flatte', Michael E.

    2004-03-01

    We present quantitative calculations for the electron g-tensors in bulk and quantum-well semiconductors based on a generalized P.p envelope function theory solved in a fourteen-band restricted basis set. The dependences of g-tensor on structure, magnetic field, carrier density, temperature, and spin polarization have been explored and will be described. It is found that at temperatures of a few Kelvin and fields of a few Tesla, the g-tensors for bulk semiconductors develop quasi-steplike dependences on carrier density or magnetic field due to magnetic quantization, and this effect is even more pronounced in quantum-well semiconductors due to the additional electric quantization along the growth direction. The influence of quantum confinement on the electron g-tensors in QWs is studied by examining the dependence of electron g-tensors on well width. Excellent agreement between these calculated electron g-tensors and measurements [1-2] is found for GaAs/AlGaAs QWs. This work was supported by DARPA/ARO. [1] A. Malinowski and R. T. Harley, Phys. Rev. B 62, 2051 (2000);[2] Le Jeune et al., Semicond. Sci. Technol. 12, 380 (1997).

  11. Multi-wavelength lasers fabricated by an Al layer controlled quantum well intermixing technology

    NASA Astrophysics Data System (ADS)

    Teng, J. H.; Chua, S. J.; Huang, Y. H.; Li, G.; Zhang, Z. H.; Helmy, A. Saher; Marsh, J. H.

    2000-09-01

    We report that the shift in the band gap of Al0.3Ga0.7As/GaAs quantum well structures can be precisely controlled by an Al layer buried between a spin-on silica film and a wet-oxidized GaAs surface. The blueshift in wavelength of the Al0.3Ga0.7As/GaAs quantum well photoluminescence (PL) depends linearly on the thickness of the buried Al layer. By changing the Al layer thickness, the PL peak wavelength can be tuned from 7870 Å for the as-grown sample to 7300 and 7050 Å after 20 and 45 s rapid thermal annealing at 850 °C, respectively. Applying this technology, Al layers with different thickness, i.e., no Al, 200 and 300 Å thick, were applied to the oxidized GaAs surface in three adjacent regions with 200 μm spacing on a quantum well laser structure sample. Three wavelength lasers were successfully fabricated in a single chip by a one step rapid thermal annealing. All the lasers have similar threshold current and slope efficiency.

  12. Scattering mechanisms in shallow undoped Si/SiGe quantum wells

    SciTech Connect

    Laroche, D.; Nielsen, E.; Lu, T. M.; Huang, S.-H.; Chuang, Y.; Li, J.-Y. Liu, C. W.

    2015-10-15

    We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ∼ 100 nm to ∼ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ n{sup α}, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ∼ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ∼ 5 is observed. We propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

  13. Classical and quantum dynamics of a periodically driven particle in a triangular well

    SciTech Connect

    Flatte, M.E.; Holthaus, M.

    1996-01-01

    We investigate the correspondence between classical and quantum mechanics for periodically time dependent Hamiltonian systems, using the example of a periodically forced particle in a one-dimensional triangular well potential. In particular, we consider quantum mechanical Floquet states associated with resonances in the classical phase space. When the classical motion exhibits subharmonic resonances, the corresponding Floquet states maintain the driving field{close_quote}s periodicity through dynamical tunneling. This principle applies both to Floquet states associated with classical invariant vortex tubes surrounding stable, elliptic periodic orbits and to Floquet states that are associated with unstable, hyperbolic periodic orbits. The triangular well model also poses a yet unsolved mathematical problem, related to perturbation theory for systems with a dense pure point spectrum. The present approximate analytical and numerical results indicate that quantum tunneling between different resonance zones is of crucial importance for the question whether the driven triangular well has a dense point or an absolutely continuous quasienergy spectrum, or whether there is a transition from the one to the other. Copyright {copyright} 1996 Academic Press, Inc.

  14. Photocurrents in semiconductors and semiconductor quantum wells analyzed by k.p-based Bloch equations

    NASA Astrophysics Data System (ADS)

    Podzimski, Reinold; Duc, Huynh Thanh; Priyadarshi, Shekhar; Schmidt, Christian; Bieler, Mark; Meier, Torsten

    2016-03-01

    Using a microscopic theory that combines k.p band structure calculations with multisubband semiconductor Bloch equations we are capable of computing coherent optically-induced rectification, injection, and shift currents in semiconductors and semiconductor nanostructures. A 14-band k.p theory has been employed to obtain electron states in non-centrosymmetric semiconductor systems. Numerical solutions of the multisubband Bloch equations provide a detailed and transparent description of the dynamics of the material excitations in terms of interband and intersubband polarizations/coherences and occupations. Our approach allows us to calculate and analyze photocurrents in the time and the frequency domains for bulk as well as quantum well and quantum wire systems with various growth directions. As examples, we present theoretical results on the rectification and shift currents in bulk GaAs and GaAs-based quantum wells. Moreover, we compare our results with experiments on shift currents. In the experiments the terahertz radiation emitted from the transient currents is detected via electro-optic sampling. This comparison is important from two perspectives. First, it helps to validate the theoretical model. Second, it allows us to investigate the microscopic origins of interesting features observed in the experiments.

  15. Growth and properties of Hg-based quantum well structures and superlattices

    NASA Technical Reports Server (NTRS)

    Schetzina, J. F.

    1990-01-01

    An overview of the properties of HgTe-CdTe quantum well structures and superlattices (SL) is presented. These new quantum structures are candidates for use as new long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) detectors, as well as for other optoelectronic applications. Much has been learned within the past two years about the physics of such structures. The valence band offset has been determined to be approx. 350 meV, independent of temperature. The occurrence of electron and hole mobilities in excess of 10(exp 5)cm(exp 2)/V center dot s is now understood on the basis of SL band structure calculations. The in-plane and out-of-plane electron and hole effective masses have been measured and interpreted theoretically for HgTe-CdTe superlattices. Controlled substitutional doping of superlattices has recently been achieved at North Carolina State University (NCSU), and modulation-doped SLs have now been successfully grown and studied. Most recently, a dramatic lowering of the growth temperature of Hg-based quantum well structure and SLs (to approx. 100 C) has been achieved by means of photoassisted molecular beam epitaxy (MBE) at NCSU. A number of new devices have been fabricated from these doped multilayers.

  16. Scattering mechanisms in shallow undoped Si/SiGe quantum wells

    SciTech Connect

    Laroche, Dominique; Huang, S. -H.; Nielsen, Erik; Chuang, Y.; Li, J. -Y.; Liu, C. W.; Lu, Tzu -Ming

    2015-10-07

    We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ~ 100 nm to ~ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ~ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ~ 5 is observed. Lastly, we propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

  17. Reversed oxygen sensing using colloidal quantum wells towards highly emissive photoresponsive varnishes

    PubMed Central

    Lorenzon, Monica; Christodoulou, Sotirios; Vaccaro, Gianfranco; Pedrini, Jacopo; Meinardi, Francesco; Moreels, Iwan; Brovelli, Sergio

    2015-01-01

    Colloidal quantum wells combine the advantages of size-tunable electronic properties with vast reactive surfaces that could allow one to realize highly emissive luminescent-sensing varnishes capable of detecting chemical agents through their reversible emission response, with great potential impact on life sciences, environmental monitoring, defence and aerospace engineering. Here we combine spectroelectrochemical measurements and spectroscopic studies in a controlled atmosphere to demonstrate the ‘reversed oxygen-sensing’ capability of CdSe colloidal quantum wells, that is, the exposure to oxygen reversibly increases their luminescence efficiency. Spectroelectrochemical experiments allow us to directly relate the sensing response to the occupancy of surface states. Magneto-optical measurements demonstrate that, under vacuum, heterostructured CdSe/CdS colloidal quantum wells stabilize in their negative trion state. The high starting emission efficiency provides a possible means to enhance the oxygen sensitivity by partially de-passivating the particle surfaces, thereby enhancing the density of unsaturated sites with a minimal cost in term of luminescence losses. PMID:25910499

  18. Resonant energy transfer between patterned InGaN/GaN quantum wells and CdSe/ZnS quantum dots.

    PubMed

    Xu, Xingsheng; Wang, Huayong

    2016-01-01

    We explore an easy method for preparation of a hybrid device of a photonic crystal InGaN/GaN quantum well (QW) and colloidal quantum dots using conventional photolithography. It is demonstrated from electroluminescence spectra that Förster resonance energy transfer takes place efficiently between the photonic crystal InGaN/GaN QW and CdSe/ZnS colloidal quantum dots. From the photoluminescence decay of the InGaN/GaN QW, the largest Förster resonance energy transfer efficiency between the photonic crystal GaN quantum well and colloidal quantum dots is measured as 88% and the corresponding Förster-resonance-energy-transfer fraction reached 42%. An easy approach is explored to realize a highly efficient electrically driven colloidal quantum dot device using the Förster-resonance-energy-transfer mechanism.

  19. Iii-V Compound Multiple Quantum Well Based Modulator and Switching Devices.

    NASA Astrophysics Data System (ADS)

    Hong, Songcheol

    A general formalism to study the absorption and photocurrent in multiple quantum well is provided with detailed consideration of quantum confined Stark shift, exciton binding energy, line broadening, tunneling, polarization, and strain effects. Results on variation of exciton size, binding energies and transition energies as a function electric field and well size have been presented. Inhomogeneous line broadening of exciton lines due to interface roughness, alloy disorder and well to well size fluctuation is calculated. The potential of material tailoring by introducing strain for specific optical response is discussed. Theoretical and experimental results on excitonic and band-to-band absorption spectra in strained multi-quantum well structures are shown. I also report on polarization dependent optical absorption for excitonic and interband transitions in lattice matched and strained multiquantum well structures in presence of transverse electric field. Photocurrent in a p-i(MQW)-n diode with monochromatic light is examined with respect to different temperatures and intensities. The negative resistance of I-V characteristic of the p-i-n diode is based on the quantum confined Stark effect of the heavy hole excitonic transition in a multiquantum well. This exciton based photocurrent characteristic allows efficient switching. A general purpose low power optical logic device using the controller-modulator concept bas been proposed and realized. The controller is a heterojunction phototransistor with multiquantum wells in the base-collector depletion region. This allows an amplified photocurrent controlled voltage feedback with low light intensity levels. Detailed analysis of the sensitivity of this device in various modes of operation is studied. Studies are also presented on the cascadability of the device as well as its integrating -thresholding properties. A multiquantum well heterojunction bipolar transistor (MHBT), which has N^+ -p^+-i(MQW)-N structure has been

  20. Coherent Pump-Probe Interactions and Terahertz Intersubband Gain in Semiconductor Quantum Wells

    NASA Technical Reports Server (NTRS)

    Liu, Ansheng; Ning, Cun-Zheng

    1999-01-01

    In recent years there has been considerable interest in intersubband-transition-based infrared semiconductor quantum well (QW) lasers because of their potential applications. In the mid-infrared range, both electrically-injected quantum cascade lasers [1] and optically-pumped multiple QW lasers [2] have been experimentally realized. In these studies, optical gain is due to population inversion between the lasing subbands. It was also proposed that stimulated Raman scattering in QW systems can produce net infrared optical gain [3j. In such a nonlinear optical scheme, the appearance of optical gain that may lead to intersubband Raman lasers does not rely on the population inversion. Since, in tile resonant Raman process (Raman gain is the largest in this case), the pump field induces population redistribution among subbands in the QW s ystem, it seems that a realistic estimate of the optical gain has to include this effect. Perturbative calculations used in the previous work [3] may overestimate the Raman gain. In this paper we present a nonperturbative calculation of terahertz gain of optically-pumped semiconductor step quantum wells. Limiting optical transitions within the conduction band of QW, we solve the pump-field-induced nonequilibrium distribution function for each subband of the QW system from a set of coupled rate equations. Both intrasubband and intersubband relaxation processes in the quantum well system are included. Taking into account the coherent interactions between pump and THz (signal) waves, we we derive the susceptibility of the QW system for the THz field. For a GaAs/AlGaAs step QW, we calculate the Thz gain spectrum for different pump frequencies and intensities. Under moderately strong pumping (approximately 0.3 MW/sq cm), a significant THz gain (approximately 300/m) is predicted. It is also shown that the coherent wave interactions (resonant stimulated Raman processes) contribute significantly to the THz gain.

  1. Energy Transfer of Excitons Between Quantum Wells Separated by a Wide Barrier

    SciTech Connect

    LYO,SUNGKWUN K.

    1999-12-06

    We present a microscopic theory of the excitonic Stokes and anti-Stokes energy transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Exciton transfer through dipolar coupling, photon-exchange coupling and over-barrier ionization of the excitons through exciton-exciton Auger processes are examined. The energy transfer rate is calculated as a function of T and the center-to-center distance d between the two wells. The rates depend sensitively on T for plane-wave excitons. For located excitons, the rates depend on T only through the T-dependence of the localization radius.

  2. Compositional dependence of the band gap in Ga(NAsP) quantum well heterostructures

    SciTech Connect

    Jandieri, K. Ludewig, P.; Wegele, T.; Beyer, A.; Kunert, B.; Springer, P.; Baranovskii, S. D.; Koch, S. W.; Volz, K.; Stolz, W.

    2015-08-14

    We present experimental and theoretical studies of the composition dependence of the direct band gap energy in Ga(NAsP)/GaP quantum well heterostructures grown on either (001) GaP- or Si-substrates. The theoretical description takes into account the band anti-crossing model for the conduction band as well as the modification of the valence subband structure due to the strain resulting from the pseudomorphic epitaxial growth on the respective substrate. The composition dependence of the direct band gap of Ga(NAsP) is obtained for a wide range of nitrogen and phosphorus contents relevant for laser applications on Si-substrate.

  3. Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain

    NASA Astrophysics Data System (ADS)

    Biermann, Mark L.; Walters, Matthew; Diaz-Barriga, James; Rabinovich, W. S.

    2003-10-01

    Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is avialable for cases of compressive anisotropic in-plane strain.

  4. Temperature dependence of the lowest excitonic transition for an InAs ultrathin quantum well

    NASA Astrophysics Data System (ADS)

    Singh, S. D.; Porwal, S.; Sharma, T. K.; Rustagi, K. C.

    2006-03-01

    Temperature dependent photoluminescence and photoreflectance techniques are used to investigate the lowest excitonic transition of InAs ultrathin quantum well. It is shown that the temperature dependence of the lowest energy transition follows the band gap variation of GaAs barrier, which is well reproduced by calculated results based on the envelope function approximation with significant corrections due to strain and temperature dependences of the confinement potential. A redshift in photoluminescence peak energy compared to photoreflectance is observed at low temperatures. This is interpreted to show that the photoluminescence signal originates from the recombination of carriers occupying the band-tail states below the lowest critical point.

  5. Generation of pure spin currents via Auger recombination in quantum wells with Rashba splitting

    SciTech Connect

    Afanasiev, A. N. Greshnov, A. A. Greshnov, A. A.

    2015-10-15

    We propose a nonoptical mechanism for generating spin current via Auger recombination in semiconductor quantum wells (QWs) with spin–orbit splitting associated with structural QW asymmetry. It is shown that Auger recombination in narrow-bandgap semiconductors makes it possible to produce spin currents that exceed those that are obtained in the case of intraband as well as interband optical excitation. Analysis shows that the interference term in the expression for the Auger-recombination rate is responsible for the generation of spin currents.

  6. Infrared transitions between hydrogenic states in GaInNAs/GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Al, E. B.; Ungan, F.; Yesilgul, U.; Kasapoglu, E.; Sari, H.; Sökmen, I.

    2016-08-01

    The effects of nitrogen and indium concentrations on the 1s, 2s, 2p0 and 2p±-like donor impurity energy states in a single Ga1‑xInxNyAs1‑y/GaAs quantum well (QW) are investigated by variational approach within the effective mass approximation. The results are presented as a function of the well width and the donor impurity position. It is found that the impurity binding and transition energies depend strongly on the indium concentration while depends weakly on the nitrogen concentration.

  7. Giant electro-optic effect in Ge/SiGe coupled quantum wells

    PubMed Central

    Frigerio, Jacopo; Vakarin, Vladyslav; Chaisakul, Papichaya; Ferretto, Marcello; Chrastina, Daniel; Le Roux, Xavier; Vivien, Laurent; Isella, Giovanni; Marris-Morini, Delphine

    2015-01-01

    Silicon-based photonics is now considered as the photonic platform for the next generation of on-chip communications. However, the development of compact and low power consumption optical modulators is still challenging. Here we report a giant electro-optic effect in Ge/SiGe coupled quantum wells. This promising effect is based on an anomalous quantum-confined Stark effect due to the separate confinement of electrons and holes in the Ge/SiGe coupled quantum wells. This phenomenon can be exploited to strongly enhance optical modulator performance with respect to the standard approaches developed so far in silicon photonics. We have measured a refractive index variation up to 2.3 × 10−3 under a bias voltage of 1.5 V, with an associated modulation efficiency VπLπ of 0.046 V cm. This demonstration paves the way for the development of efficient and high-speed phase modulators based on the Ge/SiGe material system. PMID:26477947

  8. ZnO/(ZnMg)O single quantum wells with high Mg content graded barriers

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Wassner, Thomas A.; Stutzmann, Martin; Rohnke, Marcus; Schoermann, Joerg; Eickhoff, Martin

    2012-06-01

    ZnO/Zn{sub 1-x}Mg{sub x}O single quantum wells (SQWs) were grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Compositional grading allows the application of optimized growth conditions for the fabrication of Zn{sub 1-x}Mg{sub x}O barriers with high crystalline quality and a maximum Mg content of x = 0.23. High resolution x-ray diffraction reveals partial relaxation of the graded barriers. Due to exciton localization, the SQW emission is found to consist of contributions from donor-bound and free excitons. While for narrow SQWs with well width d{sub W}{<=}2.5nm, the observed increase of the exciton binding energy is caused by quantum confinement, the drop of the photoluminescence emission below the ZnO bulk value found for wide SQWs is attributed to the quantum-confined Stark effect. For a Mg content of x = 0.23, a built-in electric field of 630 kV/cm is extracted, giving rise to a decrease of the exciton binding energy and rapid thermal quenching of the SQW emission characterized by an activation energy of (24 {+-} 4) meV for d{sub W} = 8.3 nm.

  9. Electron bilayers in an undoped Si/SiGe double-quantum-well heterostructure

    NASA Astrophysics Data System (ADS)

    Lu, Tzu-Ming; Laroche, Dominique; Huang, Shih-Hsien; Nielsen, Erik; Chuang, Yen; Li, Jiun-Yun; Liu, Cheewee

    We report the design, fabrication, and the magneto-transport study of an undoped Si/SiGe double quantum well heterostructure. We show that employing asymmetric quantum wells for our single-side-gated devices allows us to observe a cross-over from single-layer-like to bi-layer-llike behavior in the mobility-density dependence. We also observe an integer quantum Hall state at filling factor ν = 2, which is expected to arise from inter-layer effects for Si electrons. This state could be due to either inter-layer coherence, or the symmetric-antisymmetric tunneling gap. This work has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  10. Scattering mechanisms in shallow undoped Si/SiGe quantum wells

    DOE PAGES

    Laroche, Dominique; Huang, S. -H.; Nielsen, Erik; Chuang, Y.; Li, J. -Y.; Liu, C. W.; Lu, Tzu -Ming

    2015-10-07

    We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ~ 100 nm to ~ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ~ 2.3. At the highest achievable densities in the quantum wellsmore » buried at intermediate depth, an exponent α ~ 5 is observed. Lastly, we propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.« less

  11. Electrically-Tunable Group Delays Using Quantum Wells in a Distributed Bragg Reflector

    NASA Technical Reports Server (NTRS)

    Nelson, Thomas R., Jr.; Loehr, John P.; Fork, Richard L.; Cole, Spencer; Jones, Darryl K.; Keys, Andrew

    1999-01-01

    There is a growing interest in the fabrication of semiconductor optical group delay lines for the development of phased arrays of Vertical-Cavity Surface-Emitting Lasers (VCSELs). We present a novel structure incorporating In(x)GA(1-x)As quantum wells in the GaAs quarter-wave layers of a GaAs/AlAs distributed Bragg reflector (DBR). Application of an electric field across the quantum wells leads to red shifting and peak broadening of the el-hhl exciton peak via the quantum-confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. We discuss the tradeoffs between the maximum amount of change in group delay versus absorption losses for such a device. We also compare a simple theoretical model to experimental results, and discuss both angle and position tuning of the BDR band edge resonance relative to the exciton absorption peak. The advantages of such monolithically grown devices for phased-array VCSEL applications will be detailed.

  12. III-V tri-gate quantum well MOSFET: Quantum ballistic simulation study for 10 nm technology and beyond

    NASA Astrophysics Data System (ADS)

    Datta, Kanak; Khosru, Quazi D. M.

    2016-04-01

    In this work, quantum ballistic simulation study of a III-V tri-gate MOSFET has been presented. At the same time, effects of device parameter variation on ballistic, subthreshold and short channel performance is observed and presented. The ballistic simulation result has also been used to observe the electrostatic performance and Capacitance-Voltage characteristics of the device. With constant urge to keep in pace with Moore's law as well as aggressive scaling and device operation reaching near ballistic limit, a full quantum transport study at 10 nm gate length is necessary. Our simulation reveals an increase in device drain current with increasing channel cross-section. However short channel performance and subthreshold performance get degraded with channel cross-section increment. Increasing device cross-section lowers threshold voltage of the device. The effect of gate oxide thickness on ballistic device performance is also observed. Increase in top gate oxide thickness affects device performance only upto a certain value. The thickness of the top gate oxide however shows no apparent effect on device threshold voltage. The ballistic simulation study has been further used to extract ballistic injection velocity of the carrier and ballistic carrier mobility in the channel. The effect of device dimension and gate oxide thickness on ballistic velocity and effective carrier mobility is also presented.

  13. Internal quantum efficiency improvement of InGaN/GaN multiple quantum well green light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Znajdek, K.; SibińSki, M.; StrąKowska, A.; Lisik, Z.

    2016-01-01

    In recent years, GaN-based light-emitting diode (LED) has been widely used in various applications, such as RGB lighting system, full-colour display and visible-light communication. However, the internal quantum efficiency (IQE) of green LEDs is significantly lower than that of other visible spectrum LED. This phenomenon is called "green gap". This paper briefly describes the physical mechanism of the low IQE for InGaN/GaN multiple quantum well (MQW) green LED at first. The IQE of green LED is limited by the defects and the internal electric field in MQW. Subsequently, we discuss the recent progress in improving the IQE of green LED in detail. These strategies can be divided into two categories. Some of these methods were proposed to enhance crystal quality of InGaN/GaN MQW with high In composition and low density of defects by modifying the growth conditions. Other methods focused on increasing electron-hole wave function overlap by eliminating the polarization effect.

  14. Polariton condensation in a strain-compensated planar microcavity with InGaAs quantum wells

    SciTech Connect

    Cilibrizzi, Pasquale; Askitopoulos, Alexis Silva, Matteo; Lagoudakis, Pavlos G.; Bastiman, Faebian; Clarke, Edmund; Zajac, Joanna M.; Langbein, Wolfgang

    2014-11-10

    The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs{sub 0.98}P{sub 0.02} microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal space spectroscopic imaging under non-resonant optical excitation, we observe polariton condensation and a second threshold marking the onset of photon lasing, i.e., the transition from the strong to the weak-coupling regime. Condensation in a structure with suppressed photonic disorder is a necessary step towards the implementation of periodic lattices of interacting condensates, providing a platform for on chip quantum simulations.

  15. Growth and characterization of (110) InAs quantum well metamorphic heterostructures

    SciTech Connect

    Podpirka, Adrian A. Katz, Michael B.; Twigg, Mark E.; Mack, Shawn; Bennett, Brian R.; Shabani, Javad; Palmstrøm, Chris J.

    2015-06-28

    An understanding of the growth of (110) quantum wells (QWs) is of great importance to spin systems due to the observed long spin relaxation times. In this article, we report on the metamorphic growth and characterization of high mobility undoped InAs (110) QWs on GaAs (110) substrates. A low-temperature nucleation layer reduces dislocation density, results in tilting of the subsequent buffer layer and increases the electron mobility of the QW structure. The mobility varies widely and systematically (4000–16 000 cm{sup 2}/Vs at room temperature) with deposition temperature and layer thicknesses. Low-temperature transport measurements exhibit Shubnikov de-Haas oscillations and quantized plateaus in the quantum Hall regime.

  16. Demonstration of InGaN-based orange LEDs with hybrid multiple-quantum-wells structure

    NASA Astrophysics Data System (ADS)

    Iida, Daisuke; Niwa, Kazumasa; Kamiyama, Satoshi; Ohkawa, Kazuhiro

    2016-11-01

    We demonstrate the effectiveness of a hybrid multiple-quantum-wells (MQWs) structure in InGaN-based orange light-emitting diodes (LEDs) grown by metalorganic vapor phase epitaxy. The hybrid MQWs-LED is composed of orange InGaN double QWs and a blue-green InGaN single QW. Using the hybrid MQWs structure, the orange LEDs exhibited electroluminescence spectra with narrow full widths at half maximum of 51 nm at 20 mA. The light output power and external quantum efficiency of the InGaN-based orange LEDs were 0.23 mW and 0.6%, respectively, at 20 mA.

  17. Spin coherence of the two-dimensional electron gas in a GaAs quantum well

    SciTech Connect

    Larionov, A. V.

    2015-01-15

    The coherent spin dynamics of the quasi-two-dimensional electron gas in a GaAs quantum well is experimentally investigated using the time-resolved spin Kerr effect in an optical cryostat with a split coil inducing magnetic fields of up to 6 T at a temperature of about 2 K. The electron spin dephasing times and degree of anisotropy of the spin relaxation of electrons are measured in zero magnetic field at different electron densities. The dependence of the spin-orbit splitting on the electron-gas density is established. In the integral quantum-Hall-effect mode, the unsteady behavior of the spin dephasing time of 2D electrons of the lower Landau spin sublevel near the odd occupation factor ν = 3 is found. The experimentally observed unsteady behavior of the spin dephasing time can be explained in terms of new-type cyclotron modes that occur in a liquid spin texture.

  18. Room-temperature resonant tunneling of electrons in carbon nanotube junction quantum wells

    NASA Astrophysics Data System (ADS)

    Biswas, Sujit K.; Schowalter, Leo J.; Jung, Yung Joon; Vijayaraghavan, Aravind; Ajayan, Pulickel M.; Vajtai, Robert

    2005-05-01

    Resonant tunneling structures [M. Bockrath, W. Liang, D. Bozovic, J. H. Hafner, C. B. Lieber, M. Tinkham, and H. Park, Science 291, 283 (2001)], formed between the junction of two single walled nanotubes and the conductive atomic force microscopy tip contact were investigated using current sensing atomic force microscopy. Oscillations in the current voltage characteristics were measured at several positions of the investigated nanotube. The oscillatory behavior is shown to follow a simple quantum mechanical model, dependent on the energy separation in the quantum well formed within the two junctions. Our model shows that these observations seen over several hundreds of nanometers, are possible only if the scattering cross section at defects is small resulting in long phase coherence length, and if the effective mass of the carrier electrons is small. We have calculated the approximate mass of the conduction electrons to be 0.003me.

  19. Strong coupling and stimulated emission in single parabolic quantum well microcavity for terahertz cascade

    SciTech Connect

    Tzimis, A.; Savvidis, P. G.; Trifonov, A. V.; Ignatiev, I. V.; Christmann, G.; Tsintzos, S. I.; Hatzopoulos, Z.; Kavokin, A. V.

    2015-09-07

    We report observation of strong light-matter coupling in an AlGaAs microcavity (MC) with an embedded single parabolic quantum well. The parabolic potential is achieved by varying aluminum concentration along the growth direction providing equally spaced energy levels, as confirmed by Brewster angle reflectivity from a reference sample without MC. It acts as an active region of the structure which potentially allows cascaded emission of terahertz (THz) light. Spectrally and time resolved pump-probe spectroscopy reveals characteristic quantum beats whose frequencies range from 0.9 to 4.5 THz, corresponding to energy separation between relevant excitonic levels. The structure exhibits strong stimulated nonlinear emission with simultaneous transition to weak coupling regime. The present study highlights the potential of such devices for creating cascaded relaxation of bosons, which could be utilized for THz emission.

  20. Encapsulated solid phase epitaxy of a Ge quantum well embedded in an epitaxial rare earth oxide.

    PubMed

    Laha, Apurba; Bugiel, E; Jestremski, M; Ranjith, R; Fissel, A; Osten, H J

    2009-11-25

    An efficient method based on molecular beam epitaxy has been developed to integrate an epitaxial Ge quantum well buried into a single crystalline rare earth oxide. The monolithic heterostructure comprised of Gd2O3-Ge-Gd2O3 grown on an Si substrate exhibits excellent crystalline quality with atomically sharp interfaces. This heterostructure with unique structural quality could be used for novel nanoelectronic applications in quantum-effect devices such as nanoscale transistors with a high mobility channel, resonant tunneling diode/transistors, etc. A phenomenological model has been proposed to explain the epitaxial growth process of the Ge layer under oxide encapsulation using a solid source molecular beam epitaxy technique. PMID:19875877

  1. Magneto-photoluminescence of InAs/InGaAs/InAlAs quantum well structures

    SciTech Connect

    Terent'ev, Ya. V.; Danilov, S. N.; Loher, J.; Schuh, D.; Bougeard, D.; Weiss, D.; Ganichev, S. D.; Durnev, M. V.; Tarasenko, S. A.; Mukhin, M. S.; Ivanov, S. V.

    2014-03-10

    Photoluminescence (PL) and highly circularly polarized magneto-PL (up to 50% at 6 T) from two-step bandgap InAs/InGaAs/InAlAs quantum wells (QWs) are studied. Bright PL is observed up to room temperature, indicating a high quantum efficiency of the radiative recombination in these QWs. The sign of the circular polarization indicates that it stems from the spin polarization of heavy holes caused by the Zeeman effect. Although in magnetic field the PL lines are strongly circularly polarized, no energy shift between the counter-polarized PL lines was observed. The results suggest the electron and the hole g-factor to be of the same sign and close magnitudes.

  2. 1.9 THz Quantum-cascade Lasers with One-well Injector

    NASA Technical Reports Server (NTRS)

    Kumar, Sushil; Williams, Benjamin S.; Hu, Qing; Reno, John L.

    2006-01-01

    We report terahertz quantum-cascade lasers operating predominantly at 1.90 THz with side modes as low as 1.86 THz (lambda approx. equal to 161 micrometers, planck's constant omega approx. equal to 7.7 meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-sink temperature of 110 K in pulsed mode, 95 K in continuous wave (cw) mode, and the threshold current density at 5 K was approx. 140 A per square centimeters.

  3. Recent progress in quantum well infrared photodetector research and development at Jet Propulsion Lab.

    NASA Astrophysics Data System (ADS)

    Krabach, Timothy N.; Gunapala, Sarath D.; Bandara, Sumith V.; Liu, John K.; Pool, Frederick S.; Sengupta, Deepak K.; Shott, C. A.; Carralejo, Ronald J.; Stetson, Norman B.

    1998-04-01

    One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the quantum well IR photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128 X 128 QWIP focal plane array camera, hand-held and palmsize 256 X 256 long wavelength QWIP cameras and 648 X 480 long-wavelength cameras, holding forth great promise for myriad applications in 6-25 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in broadband QWIPs and mid-wave long-wave dualband QWIPs at Jet Propulsion Lab for various NASA and DOD applications.

  4. Microwave spectroscopy of the low-filling-factor bilayer electron solid in a wide quantum well

    PubMed Central

    Hatke, A. T.; Liu, Y.; Engel, L. W.; Shayegan, M.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.

    2015-01-01

    At the low Landau filling factor termination of the fractional quantum Hall effect series, two-dimensional electron systems exhibit an insulating phase that is understood as a form of pinned Wigner solid. Here we use microwave spectroscopy to probe the transition to the insulator for a wide quantum well sample that can support single-layer or bilayer states depending on its overall carrier density. We find that the insulator exhibits a resonance which is characteristic of a bilayer solid. The resonance also reveals a pair of transitions within the solid, which are not accessible to dc transport measurements. As density is biased deeper into the bilayer solid regime, the resonance grows in specific intensity, and the transitions within the insulator disappear. These behaviours are suggestive of a picture of the insulating phase as an emulsion of liquid and solid components. PMID:25947282

  5. Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface

    SciTech Connect

    Simmons, J.A.; Harff, N.E.; Lyo, S.K.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.

    1997-12-31

    By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data.

  6. Polarization-dependent exciton linewidth in semiconductor quantum wells: A consequence of bosonic nature of excitons

    NASA Astrophysics Data System (ADS)

    Singh, Rohan; Suzuki, Takeshi; Autry, Travis M.; Moody, Galan; Siemens, Mark E.; Cundiff, Steven T.

    2016-08-01

    The exciton coherent signal decay rate in GaAs quantum wells, as measured in four-wave mixing experiments, depends on the polarization of the excitation pulses. Using polarization-dependent two-dimensional coherent spectroscopy, we show that this behavior is due to the bosonic character of excitons. Interference between two different quantum mechanical pathways results in a smaller decay rate for cocircular and colinear polarization of the optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a larger decay rate. Our result shows that the bosonic nature of excitons must be considered when interpreting ultrafast spectroscopic studies of exciton dephasing in semiconductors. This behavior should be considered while interpreting results of ultrafast spectroscopy experiments involving bosonlike excitations.

  7. Theory of light-induced drift of electrons in coupled quantum wells

    NASA Astrophysics Data System (ADS)

    Stockman, Mark I.; Muratov, Leonid S.; George, Thomas F.

    1992-10-01

    A theory of the new effect of light-induced drift (LID) in coupled potential wells is developed on the basis of the density-matrix method. The effect appears when light excites intersubband electronic transitions. LID manifests itself as the photocurrent of the two-dimensional electron gas in the well plane, which depends on coherent electron tunneling between the coupled wells. The theory shows the effect to possess distinctive features such as a characteristic antisymmetric spectral contour consisting of four alternating positive and negative peaks and the change of sign of the LID current with the sign change of the bias normal to the quantum-well plane. The quantitative estimates for GaAs wells show the LID current to be readily detectable.

  8. Characterization of AlGaN epitaxial layer

    NASA Astrophysics Data System (ADS)

    Parasuraman, Usha; Srinivasan, Sridhar; Ponce, Fernando; Rong, Liu; Abigail, Bell; Mei, Justin; Tanaka, S.

    2003-10-01

    Accurate aluminum compositions have been determined for AlxGa1-xN alloys whose rough compositions vary between 0AlGaN layer. TEM pictures showed the absence of misfit dislocations in the basal plane which indicated that the AlGaN layer was indeed under pseudomorphic growth. This study allows us to conclude that RBS is not a suitable technique for estimating the composition in the case of light elements such as Al. Cathodoluminescence was done to determine the band gap and the bowing parameter was calculated for the composition range 0

  9. Demonstration of a bias tunable quantum dots-in-a-well focal plane array

    NASA Astrophysics Data System (ADS)

    Andrews, Jonathan; Jang, Woo-Yong; Pezoa, Jorge E.; Sharma, Yagya D.; Lee, Sang Jun; Noh, Sam Kyu; Hayat, Majeed M.; Restaino, Sergio; Teare, Scott W.; Krishna, Sanjay

    2009-11-01

    Infrared detectors based on quantum wells and quantum dots have attracted a lot of attention in the past few years. Our previous research has reported on the development of the first generation of quantum dots-in-a-well (DWELL) focal plane arrays, which are based on InAs quantum dots embedded in an InGaAs well having GaAs barriers. This focal plane array has successfully generated a two-color imagery in the mid-wave infrared (i.e. 3-5 μm) and the long-wave infrared (i.e. 8-12 μm) at a fixed bias voltage. Recently, the DWELL device has been further modified by embedding InAs quantum dots in InGaAs and GaAs double wells with AlGaAs barriers, leading to a less strained InAs/InGaAs/GaAs/AlGaAs heterostructure. This is expected to improve the operating temperature while maintaining a low dark current level. This paper examines 320 × 256 double DWELL based focal plane arrays that have been fabricated and hybridized with an Indigo 9705 read-out integrated circuit using Indium-bump (flip-chip) technology. The spectral tunability is quantified by examining images and determining the transmittance ratio (equivalent to the photocurrent ratio) between mid-wave and long-way infrared filter targets. Calculations were performed for a bias range from 0.3 to 1.0 V. The results demonstrate that the mid-wave transmittance dominates at these low bias voltages, and the transmittance ratio continuously varies over different applied biases. Additionally, radiometric characterization, including array uniformity and measured noise equivalent temperature difference for the double DWELL devices is computed and compared to the same results from the original first generation DWELL. Finally, higher temperature operation is explored. Overall, the double DWELL devices had lower noise equivalent temperature difference and higher uniformity, and worked at higher temperature (70 K and 80 K) than the first generation DWELL device.

  10. Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

    SciTech Connect

    Hammersley, S.; Dawson, P.; Kappers, M. J.; Massabuau, F. C.-P.; Sahonta, S.-L.; Oliver, R. A.; Humphreys, C. J.

    2015-09-28

    InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.

  11. Excitonic field screening and bleaching in InGaN/GaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Chen, Fei; Kirkey, W. D.; Furis, M.; Cheung, M. C.; Cartwright, A. N.

    2003-03-01

    Photoinduced carrier dynamics in a sequence of InGaN/GaN multiple quantum wells (MQWs) are studied by employing steady state and ultrafast spectroscopy at room temperature. Time-resolved photoluminescence (PL) measured short carrier lifetimes of ˜140 ps at room temperature. Steady state differential transmission was used to measure the in-well field screening due to the photoinjected carriers. The observed offset in emission energy from excitonic screening energies is consistent with the emission of carriers through localized states slightly below the excitonic resonance energy. Furthermore, time-resolved differential transmission with amplified pulses, where significant carrier densities can be optically generated, provides evidence of both excitonic bleaching and field screening in these InGaN quantum wells (QWs). The comparison of the time-resolved differential absorption spectra at various carrier densities allows us to identify different carrier recombination dynamics in the InGaN well and to separate the field screening from the bleaching effects. Finally, the extreme prolongation of the carrier recombination lifetime up to ˜4 μs suggests the spatial separation between electrons and holes under the large in-well fields.

  12. Multi-Quantum Well Structures to Improve the Performance of Multijunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Samberg, Joshua Paul

    Current, lattice matched triple junction solar cell efficiency is approximately 44% at a solar concentration of 942x. Higher efficiency for such cells can be realized with the development of a 1eV bandgap material lattice matched to Ge. One of the more promising materials for this application is that of the InGaAs/GaAsP multi-quantum well (MQW) structure. By inserting a stress/strain-balanced InGaAs/GaAsP MQW structure into the iregion of a GaAs p-i-n diode, the absorption edge of the p-i-n diode can be red shifted with respect to that of a standard GaAs p-n diode. Compressive stress in the InGaAs wells are balanced via GaAsP barriers subjected to tensile stress. Individually, the InGaAs and GaAsP layers are grown below their critical layer thickness to prevent the formation of misfit and threading dislocations. Until recently InGaAs/GaAsP MQWs have been somewhat hindered by their usage of low phosphorus-GaAsP barriers. Presented within is the development of a high-P composition GaAsP and the merits for using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high composition GaAsP the carriers are collected via tunneling (for barriers .30A) as opposed to thermionic emission. Thus, by utilizing thin, high content GaAsP barriers one can increase the percentage of the intrinsic region in a p-i-n structure that is comprised of the InGaAs well in addition to increasing the number of periods that can be grown for a given depletion width. However, standard MQWs of this type inherently possess undesirable compressive strain and quantum size effects (QSE) that cause the optical absorption of the InGaAs wells to blue shift. To circumvent these deleterious QSEs stress balanced, pseudomorphic InGaAs/GaAsP staggered MQWs were developed. Tunneling is still a viable mode for carrier transport in the staggered MQW structures. GaAs interfacial layers within the multi-quantum

  13. Temperature scaling in the quantum-Hall-effect regime in a HgTe quantum well with an inverted energy spectrum

    SciTech Connect

    Arapov, Yu. G.; Gudina, S. V.; Neverov, V. N.; Podgornykh, S. M.; Popov, M. R. Harus, G. I.; Shelushinina, N. G.; Yakunin, M. V.; Mikhailov, N. N.; Dvoretsky, S. A.

    2015-12-15

    The longitudinal and Hall magnetoresistances of HgTe/HgCdTe heterostructures with an inverted energy spectrum (the HgTe quantum well width is d = 20.3 nm) are measured in the quantum-Hall-effect regime at T = 2–50 K in magnetic fields up to B = 9 T. Analysis of the temperature dependences of conductivity in the transition region between the first and second plateaus of the quantum Hall effect shows the feasibility of the scaling regime for a plateau–plateau quantum phase transition in 2D-structures on the basis of mercury telluride.

  14. Quantum-confined Stark effect on spatially indirect excitons in CdTe/Cdx Zn1-x Te quantum wells

    NASA Astrophysics Data System (ADS)

    Haas, H.; Magnea, N.; Dang, Le Si

    1997-01-01

    The quantum-confined Stark effect is studied in the mixed type-I/type-II CdTe/Cdx Zn1-x Te strained heterostructures. The type-II nature of the light-hole excitons is unambiguously confirmed by the blueshift observed under increasing electric field, in good agreement with calculations. On the other hand, the heavy-hole excitons are redshifted as expected for type-I excitons. The peculiar valence-band alignment, resulting from the sign reversal of the strain between the wells and the barriers, is used to detect the electric-field induced mixing of LH1 and HH2 confined hole states. An accurate value for the long-disputed chemical valence-band offset of CdTe/ZnTe system is extracted as ΔEV=(11+/-3)% of the band-gap difference between unstrained CdTe and ZnTe materials.

  15. Diamagnetic susceptibility: An indicator of pressure induced donor localization in a double quantum well

    NASA Astrophysics Data System (ADS)

    Vignesh, G.; Nithiananthi, P.

    2016-04-01

    The influence of pressure along the growth axis on carrier localization in GaAs/Al0.3Ga0.7As Double Quantum Well (DQW) is studied under strongly coupled regime and isolated regimes of the well. The effective mass approximation combined with variation technique is adopted with the inclusion of mismatches in effective mass and dielectric constants of the well and barrier material. Effect of the barrier and well on carrier localization is investigated by observing the diamagnetic susceptibility (χdia) for various impurity locations (zi) and the critical limit of the barrier (Lb ≈ 50 Å) for tunneling has also been estimated. The effect of Γ-Χ crossover due to the application of pressure on the donor localization is picturized through diamagnetic susceptibility.

  16. Modeling the band gap of CdS quantum well structures

    NASA Astrophysics Data System (ADS)

    Harris, R. A.; Terblans, J. J.

    2016-10-01

    Within the framework of the effective mass approximation, an excited electron is studied in a cadmium sulfide (CdS) quantum well with varying well widths. The envelope function approximation is employed involving a three parameter variational calculation wherein one of these parameters is the distance between the electron and the hole. The relative change in the electron's energy (relative to its energy when it is in the valence band; in the hole) is investigated as a function of the electron-hole distance. Results from numerical calculations are presented and the non-linear behavior of different sized CdS quantum wells are discussed. Comparisons between experimentally measured CdS band gap energies (as a function of well-width) and the simulation data are made. A good agreement between the current model and experimental data exists. Density functional theory (DFT) calculations are done on crystallites of extremely small sizes to compare the current model's bandgap energies to DFT-predicted bandgap values at these extremes.

  17. Transport properties of silicon complementary-metal-oxide semiconductor quantum well field-effect transistors

    NASA Astrophysics Data System (ADS)

    Naquin, Clint Alan

    Introducing explicit quantum transport into silicon (Si) transistors in a manner compatible with industrial fabrication has proven challenging, yet has the potential to transform the performance horizons of large scale integrated Si devices and circuits. Explicit quantum transport as evidenced by negative differential transconductances (NDTCs) has been observed in a set of quantum well (QW) n-channel metal-oxide-semiconductor (NMOS) transistors fabricated using industrial silicon complementary MOS processing. The QW potential was formed via lateral ion implantation doping on a commercial 45 nm technology node process line, and measurements of the transfer characteristics show NDTCs up to room temperature. Detailed gate length and temperature dependence characteristics of the NDTCs in these devices have been measured. Gate length dependence of NDTCs shows a correlation of the interface channel length with the number of NDTCs formed as well as with the gate voltage (VG) spacing between NDTCs. The VG spacing between multiple NDTCs suggests a quasi-parabolic QW potential profile. The temperature dependence is consistent with partial freeze-out of carrier concentration against a degenerately doped background. A folding amplifier frequency multiplier circuit using a single QW NMOS transistor to generate a folded current-voltage transfer function via a NDTC was demonstrated. Time domain data shows frequency doubling in the kHz range at room temperature, and Fourier analysis confirms that the output is dominated by the second harmonic of the input. De-embedding the circuit response characteristics from parasitic cable and contact impedances suggests that in the absence of parasitics the doubling bandwidth could be as high as 10 GHz in a monolithic integrated circuit, limited by the transresistance magnitude of the QW NMOS. This is the first example of a QW device fabricated by mainstream Si CMOS technology being used in a circuit application and establishes the feasibility

  18. Wavelength-dependent femtosecond pulse amplification in wideband tapered-waveguide quantum well semiconductor optical amplifiers.

    PubMed

    Xia, Mingjun; Ghafouri-Shiraz, H

    2015-12-10

    In this paper, we study the wavelength-dependent amplification in three different wideband quantum well semiconductor optical amplifiers (QWAs) having conventional, exponentially tapered, and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in the quantum well is established based on a quantum well transmission line modeling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain, and the output spectra of the amplified pulse in all three structures exhibit an apparent redshift and bandwidth narrowing due to the reduction of carrier density; however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplification of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependence of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of a femtosecond pulse train, the linear-tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs.

  19. Wavelength-dependent femtosecond pulse amplification in wideband tapered-waveguide quantum well semiconductor optical amplifiers.

    PubMed

    Xia, Mingjun; Ghafouri-Shiraz, H

    2015-12-10

    In this paper, we study the wavelength-dependent amplification in three different wideband quantum well semiconductor optical amplifiers (QWAs) having conventional, exponentially tapered, and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in the quantum well is established based on a quantum well transmission line modeling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain, and the output spectra of the amplified pulse in all three structures exhibit an apparent redshift and bandwidth narrowing due to the reduction of carrier density; however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplification of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependence of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of a femtosecond pulse train, the linear-tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs. PMID

  20. Dependence of radiative and nonradiative recombination on carrier density and Al content in thick AlGaN epilayers

    NASA Astrophysics Data System (ADS)

    Podlipskas, Ž.; Aleksiejūnas, R.; Kadys, A.; Mickevičius, J.; Jurkevičius, J.; Tamulaitis, G.; Shur, M.; Shatalov, M.; Yang, J.; Gaska, R.

    2016-04-01

    Dynamics of radiative and nonradiative recombination of non-equilibrium carriers is investigated in thick AlGaN epitaxial layers with Al content ranging from 0.11 to 0.71. The internal quantum efficiency (IQE) in the epilayers was obtained using two approaches: either estimated from PL measurements or calculated using the recombination coefficients of a simple ABC model, retrieved by fitting the kinetics of light induced transient gratings (LITG). At photoexcited carrier densities below ~1019 cm-3, both approaches provided similar IQE values indicating that the simple ABC model is applicable to analyze carrier recombination at such carrier densities. The increase in IQE at higher carrier densities slowed down for the values extracted from PL considerably faster than for those obtained from LITG transients. This discrepancy is explained in terms of the mixed nature of the rate coefficient B caused by the onset of the density-activated nonradiative recombination at high carrier densities.

  1. First-principles theory of quantum well resonance in double barrier magnetic tunnel junctions.

    PubMed

    Wang, Yan; Lu, Zhong-Yi; Zhang, X-G; Han, X F

    2006-08-25

    Quantum well (QW) resonances in Fe(001)/MgO/Fe/MgO/Fe double barrier magnetic tunnel junctions are calculated from first principles. By including the Coulomb blockade energy due to the finite size islands of the middle Fe film, we confirm that the oscillatory differential resistance observed in a recent experiment [T. Nozaki, Phys. Rev. Lett. 96, 027208 (2006)10.1103/PhysRevLett.96.027208] originates from the QW resonances from the Delta1 band of the Fe majority-spin channel. The primary source of smearing at low temperatures is shown to be the variation of the Coulomb blockade energy.

  2. Electronic properties of substitutional impurities in InGaN monolayer quantum wells

    SciTech Connect

    Alfieri, G.; Tsutsumi, T.; Micheletto, R.

    2015-05-11

    InGaN alloys and, in particular, InGaN monolayer quantum wells (MLQWs) are attracting an increasing amount of interest for opto-electronic applications. Impurities, incorporated during growth, can introduce electronic states that can degrade the performance of such devices. For this reason, we present a density functional and group theoretical study of the electronic properties of C, H, or O impurities in an InGaN MLQW. Analysis of the formation energy and symmetry reveals that these impurities are mostly donors and can be held accountable for the reported degradation of InGaN-based devices.

  3. Electric-field-induced mid-infrared birefringence of the double quantum wells

    NASA Astrophysics Data System (ADS)

    Vinnichenko, M. Ya; Babich, V. M.; Balagula, R. M.; Sofronov, A. N.; Firsov, D. A.; Vorobjev, L. E.

    2016-08-01

    Birefringence in double tunnel-coupled GaAs/AlGaAs quantum wells was studied in the mid-infrared spectral range close to the intersubband resonance. Phase-sensitive optical studies allowed us to deduce simultaneously the differences of the refraction index and absorption coefficient for the normal waves polarized in the plane of the structure and along the structure growth, including electric-field induced effects. The optical absorption data are in a good agreement with the direct optical transmission measurements.

  4. Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.

    PubMed

    Goryca, M; Ferrand, D; Kossacki, P; Nawrocki, M; Pacuski, W; Maślana, W; Gaj, J A; Tatarenko, S; Cibert, J; Wojtowicz, T; Karczewski, G

    2009-01-30

    The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

  5. Temperature stability of intersubband transitions in AlN/GaN quantum wells

    SciTech Connect

    Berland, Kristian; Stattin, Martin; Farivar, Rashid; Sultan, D. M. S.; Hyldgaard, Per; Larsson, Anders; Wang, Shu Min; Andersson, Thorvald G.

    2010-07-26

    Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400 deg. C. The self-consistent Schroedinger-Poisson modeling includes temperature effects of the band gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by approx6 meV at 400 deg. C relative to its room temperature value.

  6. Resonant intersubband plasmon induced current in InGaAs quantum wells on GaAs

    SciTech Connect

    Holzbauer, Martin Klang, Pavel; Detz, Hermann; Maxwell Andrews, Aaron; Strasser, Gottfried; Gornik, Erich; Bakshi, Pradip

    2014-03-24

    We present measurements of the current enhancement due to the coupling of two intersubband plasmons in In{sub 0.05}Ga{sub 0.95}As quantum wells. With changing bias, an emissive and an absorptive intersubband plasmon mode cross attractively and trapped electrons in the ground state gain enough energy from the plasma wave to be lifted up to the second subband, where they can contribute to the current. This effect can be directly observed as an increase of 33% in the current. A magnetic field applied parallel to the growth direction allows a control of the strength of the intersubband plasmon coupling up to a quenching.

  7. Silicon-Germanium multi-quantum well photodetectors in the near infrared.

    PubMed

    Onaran, Efe; Onbasli, M Cengiz; Yesilyurt, Alper; Yu, Hyun Yong; Nayfeh, Ammar M; Okyay, Ali K

    2012-03-26

    Single crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ~10 mA/cm² and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage.

  8. AlxGa1-xAs Single-Quantum-Well Surface-Emitting Lasers

    NASA Technical Reports Server (NTRS)

    Kim, Jae H.

    1992-01-01

    Surface-emitting solid-state laser contains edge-emitting Al0.08Ga0.92As single-quantum-well (SQW) active layer sandwiched between graded-index-of-refraction separate-confinement-heterostructure (GRINSCH) layers of AlxGa1-xAs, includes etched 90 degree mirrors and 45 degree facets to direct edge-emitted beam perpendicular to top surface. Laser resembles those described in "Pseudomorphic-InxGa1-xAs Surface-Emitting Lasers" (NPO-18243). Suitable for incorporation into optoelectronic integrated circuits for photonic computing; e.g., optoelectronic neural networks.

  9. Magnetic Semiconductor Quantum Wells in High Fields to 60 Tesla: Photoluminescence Linewidth Annealing at Magnetization Steps

    SciTech Connect

    Awschalom, D.D.; Crooker, S.A.; Lyo, S.K.; Rickel, D.G.; Samarth, N.

    1999-05-24

    Magnetic semiconductors offer a unique possibility for strongly tuning the intrinsic alloy disorder potential with applied magnetic field. We report the direct observation of a series of step-like reductions in the magnetic alloy disorder potential in single ZnSe/Zn(Cd,Mn)Se quantum wells between O and 60 Tesla. This disorder, measured through the linewidth of low temperature photoluminescence spectra drops abruptly at -19, 36, and 53 Tesla, in concert with observed magnetization steps. Conventional models of alloy disorder (developed for nonmagnetic semiconductors) reproduce the general shape of the data, but markedly underestimate the size of the linewidth reduction.

  10. Lateral carrier confinement in InGaN quantum-well nanorods

    SciTech Connect

    Shi, Chentian; Zhang, Chunfeng; Wang, Xiaoyong; Xiao, Min

    2015-07-15

    We review our studies on lateral carrier diffusion in micro-fabricated samples of InGaN nanorods and their parent quantum wells. The carrier diffusion is observed to be strongly confined in nanorods, as manifested by the reduction in the delayed-rise component of time-resolved photoluminescence traces. We further argue that the confinement of carrier diffusion can be applied to suppress the efficiency droop related to defect state recombination and to assist in the energy transfer between InGaN nanorods and nanocrystal phosphors for color conversion.

  11. Suppression of bulk conductivity in InAs/GaSb broken gap composite quantum wells

    SciTech Connect

    Charpentier, Christophe; Fält, Stefan; Reichl, Christian; Nichele, Fabrizio; Nath Pal, Atindra; Pietsch, Patrick; Ihn, Thomas; Ensslin, Klaus; Wegscheider, Werner

    2013-09-09

    The two-dimensional topological insulator state in InAs/GaSb quantum wells manifests itself by topologically protected helical edge channel transport relying on an insulating bulk. This work investigates a way of suppressing bulk conductivity by using gallium source materials of different degrees of impurity concentrations. While highest-purity gallium is accompanied by clear conduction through the sample bulk, intentional impurity incorporation leads to a bulk resistance over 1 MΩ, independent of applied magnetic fields. In addition, ultra high electron mobilities for GaAs/AlGaAs structures fabricated in a molecular beam epitaxy system used for the growth of Sb-based samples are reported.

  12. Limitation of electron mobility from hyperfine interaction in ultraclean quantum wells and topological insulators

    NASA Astrophysics Data System (ADS)

    Tarasenko, S. A.; Burkard, Guido

    2016-07-01

    The study of electron transport and scattering processes limiting electron mobility in high-quality semiconductor structures is central to solid-state electronics. Here, we uncover an unavoidable source of electron scattering which is caused by fluctuations of nuclear spins. We calculate the momentum relaxation time of electrons in quantum wells governed by the hyperfine interaction between electrons and nuclei and show that this time depends greatly on the spatial correlation of nuclear spins. Moreover, the scattering processes accompanied by a spin flip are a source of the backscattering of Dirac fermions at conducting surfaces of topological insulators.

  13. Exciton photoluminescence in resonant quasi-periodic Thue-Morse quantum wells.

    PubMed

    Hsueh, W J; Chang, C H; Lin, C T

    2014-02-01

    This Letter investigates exciton photoluminescence (PL) in resonant quasi-periodic Thue-Morse quantum wells (QWs). The results show that the PL properties of quasi-periodic Thue-Morse QWs are quite different from those of resonant Fibonacci QWs. The maximum and minimum PL intensities occur under the anti-Bragg and Bragg conditions, respectively. The maxima of the PL intensity gradually decline when the filling factor increases from 0.25 to 0.5. Accordingly, the squared electric field at the QWs decreases as the Thue-Morse QW deviates from the anti-Bragg condition. PMID:24487847

  14. Controllable optical bistability and multistability in asymmetric double quantum wells via spontaneously generated coherence

    SciTech Connect

    Chen, Yuan; Deng, Li; Chen, Aixi

    2015-02-15

    We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device.

  15. Hybrid single quantum well InP/Si nanobeam lasers for silicon photonics.

    PubMed

    Fegadolli, William S; Kim, Se-Heon; Postigo, Pablo Aitor; Scherer, Axel

    2013-11-15

    We report on a hybrid InP/Si photonic crystal nanobeam laser emitting at 1578 nm with a low threshold power of ~14.7 μW. Laser gain is provided from a single InAsP quantum well embedded in a 155 nm InP layer bonded on a standard silicon-on-insulator wafer. This miniaturized nanolaser, with an extremely small modal volume of 0.375(λ/n)(3), is a promising and efficient light source for silicon photonics.

  16. Fermi surface and quantum well states of V(110) films on W(110)

    NASA Astrophysics Data System (ADS)

    Krupin, Oleg; Rotenberg, Eli; Kevan, S. D.

    2007-09-01

    Using angle-resolved photoemission spectroscopy, we have measured the Fermi surface of V(110) films epitaxially grown on a W(110) substrate. We compare our results for thicker films to existing calculations and measurements for bulk vanadium and find generally very good agreement. For thinner films, we observe and analyse a diverse array of quantum well states that split and distort the Fermi surface segments. We have searched unsuccessfully for a thickness-induced topological transition associated with contact between the zone-centre jungle gym and zone-boundary hole ellipsoid Fermi surface segments. We also find no evidence for ferromagnetic splitting of any bands on this surface.

  17. Monolithic arrays of grating-surface-emitting diode lasers and quantum well modulators for optical communications

    NASA Technical Reports Server (NTRS)

    Carlson, N. W.; Evans, G. A.; Liew, S. K.; Kaiser, C. J.

    1990-01-01

    The electro-optic switching properties of injection-coupled coherent 2-D grating-surface-emitting laser arrays with multiple gain sections and quantum well active layers are discussed and demonstrated. Within such an array of injection-coupled grating-surface-emitting lasers, a single gain section can be operated as intra-cavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient sub-nanosecond switching of high power grading-surface-emitting laser arrays by using only one gain section as an intra-cavity loss modulator.

  18. Optical logic using electrically connected quantum well PIN diode modulators and detectors.

    PubMed

    Lentine, A L; Miller, D A; Henry, J E; Cunningham, J E; Chirovsky, L M; D'Asaro, L A

    1990-05-10

    We present new optoelectronic logic devices or circuits consisting of electrically connected quantum well PIN diodes capable of implementing any boolean logic function. One class of circuits uses single beams to represent the logic levels and compares their intensities to a locally generated reference signal. A second class of circuits routes signals as differential pairs. The connections of diodes in these circuits resemble the transistor connections in NMOS and CMOS logic families. We demonstrate simple optical programmable logic arrays (e.g., E = AB + CD) using both of these classes of circuits. PMID:20563144

  19. Polariton Resonances for Ultrastrong Coupling Cavity Optomechanics in GaAs/AlAs Multiple Quantum Wells.

    PubMed

    Jusserand, B; Poddubny, A N; Poshakinskiy, A V; Fainstein, A; Lemaitre, A

    2015-12-31

    Polariton-mediated light-sound interaction is investigated through resonant Brillouin scattering experiments in GaAs/AlAs multiple-quantum wells. Photoelastic coupling enhancement at exciton-polariton resonance reaches 10(5) at 30 K as compared to a typical bulk solid room temperature transparency value. When applied to GaAs based cavity optomechanical nanodevices, this result opens the path to huge displacement sensitivities and to ultrastrong coupling regimes in cavity optomechanics with couplings g(0) in the range of 100 GHz. PMID:26765028

  20. Two-Color Photoexcitation in a GaNAs/AlGaAs Quantum Well Solar Cell

    NASA Astrophysics Data System (ADS)

    Elborg, Martin; Jo, Masafumi; Ding, Yi; Noda, Takeshi; Mano, Takaaki; Sakoda, Kazuaki

    2012-06-01

    We demonstrate an efficient two-color photoexcitation process in a GaNAs/AlGaAs multiple quantum well (MQW) solar cell. The introduction of N into the GaAs MQW induces a marked reduction in bandgap energy, forming a large conduction band offset, and the formation of localized states. Owning to this deep confinement, the thermal escape of photogenerated carriers from the QWs is greatly suppressed even at room temperature, resulting in a reduction in photocurrent. An additional photocurrent is generated by a two-color absorption process of sub-bandgap photons.

  1. Multiband electron resonant Raman scattering in quantum wells in a magnetic field

    NASA Astrophysics Data System (ADS)

    López-Richard, V.; Hai, G.-Q.; Trallero-Giner, C.; Marques, G. E.

    2003-04-01

    A theoretical model has been developed for the electronic resonant Raman scattering processes in direct band zinc blende type semiconductor quantum wells in a magnetic field. In order to take into account the spin-flip transitions, anomalous behavior of the Landau levels and the Landè g factor, an 8×8 Kane-Weiler Hamiltonian model has been considered for the evaluation of the Raman scattering amplitude. Elements concerning the selection rules of resonant inelastic light scattering in quantum well systems are reported. The multiband model predicts conditions for resonant spin-flip Raman processes in several light scattering configurations for crossed and parallel polarization. Special emphasis is given to the effects of the interlevel coupling and mixing within the conduction subband and their relation to spin-flip and inter-Landau level transitions. Symmetry and electronic properties of the level structure in the first conduction subband as well as anomalous Landè factors are discussed in terms of complementary Raman scattering configurations, Fermi energy, and multiband parameters.

  2. Mobility modulation in inverted delta doped coupled double quantum well structure

    NASA Astrophysics Data System (ADS)

    Sahoo, N.; Sahu, T.

    2016-10-01

    We have studied the modulation of electron mobility μ as a function of the electric field perpendicular to the interface plane Fp in a GaAs/AlGaAs double quantum well structure near the resonance of subband states. The functional dependence of μ on Fp exhibits a minimum near the anticrossing of subband states leading to an oscillatory behavior of μ. We show that the oscillatory enhancement of μ becomes more pronounced with increase in the difference between the doping concentrations in the side barriers. The oscillation of μ also increases by varying the widths of the two wells through shifting of the position of the middle barrier. It is interesting to show that the oscillation of μ is always larger when there is doping in barrier towards the substrate side compared to that of the surface side due to the difference in the influence of the interface roughness scattering potential. Further, broadening of the central barrier width increases the peaks of the oscillation of μ mostly due to the changes in the ionized impurity scattering potential. Our results can be utilized for the performance enhancement of quantum well field effect transistor devices.

  3. Quantum transport of bosonic cold atoms in double-well optical lattices

    SciTech Connect

    Qian Yinyin; Gong Ming; Zhang Chuanwei

    2011-07-15

    We numerically investigate, using the time evolving block decimation algorithm, the quantum transport of ultracold bosonic atoms in a double-well optical lattice through slow and periodic modulation of the lattice parameters (intra- and inter-well tunneling, chemical potential, etc.). The transport of atoms does not depend on the rate of change of the parameters (as along as the change is slow) and can distribute atoms in optical lattices at the quantized level without involving external forces. The transport of atoms depends on the atom filling in each double well and the interaction between atoms. In the strongly interacting region, the bosonic atoms share the same transport properties as noninteracting fermions with quantized transport at the half filling and no atom transport at the integer filling. In the weakly interacting region, the number of the transported atoms is proportional to the atom filling. We show the signature of the quantum transport from the momentum distribution of atoms that can be measured in the time-of-flight image. A semiclassical transport model is developed to explain the numerically observed transport of bosonic atoms in the noninteracting and strongly interacting limits. The scheme may serve as an quantized battery for atomtronics applications.

  4. High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same

    NASA Technical Reports Server (NTRS)

    Welser, Roger E. (Inventor); Sood, Ashok K. (Inventor)

    2014-01-01

    Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.

  5. Bound states for multiple Dirac-δ wells in space-fractional quantum mechanics

    SciTech Connect

    Tare, Jeffrey D. Esguerra, Jose Perico H.

    2014-01-15

    Using the momentum-space approach, we obtain bound states for multiple Dirac-δ wells in the framework of space-fractional quantum mechanics. Introducing first an attractive Dirac-comb potential, i.e., Dirac comb with strength −g (g > 0), in the space-fractional Schrödinger equation we show that the problem of obtaining eigenenergies of a system with N Dirac-δ wells can be reduced to a problem of obtaining the eigenvalues of an N × N matrix. As an illustration we use the present matrix formulation to derive expressions satisfied by the bound-state energies of N = 1, 2, 3 delta wells. We also obtain the corresponding wave functions and express them in terms of Fox's H-function.

  6. Many-Body Effect in Spin Dephasing in n-Type GaAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Weng, Ming-Qi; Wu, Ming-Wei

    2005-03-01

    By constructing and numerically solving the kinetic Bloch equations we perform a many-body study of the spin dephasing due to the D'yakonov-Perel' effect in n-type GaAs (100) quantum wells for high temperatures. In our study, we include the spin-conserving scattering such as the electron-phonon, the electron-nonmagnetic impurity as well as the electron-electron Coulomb scattering into consideration. The dephasing obtained from our theory contains both the single-particle and the many-body contributions with the latter originating from the inhomogeneous broadening introduced by the DP term [J. Supercond.: Incorp. Novel Magn. 14 (2001) 245 Eur. Phys. J. B 18 (2000) 373]. Our result agrees very well with the experimental data [Phys. Rev. B 62 (2000) 13034] of Malinowski et al. We further show that in the case we study, the spin dephasing is dominated by the many-body effect.

  7. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    NASA Astrophysics Data System (ADS)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  8. InGaP-based quantum well solar cells: Growth, structural design, and photovoltaic properties

    NASA Astrophysics Data System (ADS)

    Hashem, Islam E.; Zachary Carlin, C.; Hagar, Brandon G.; Colter, Peter C.; Bedair, S. M.

    2016-03-01

    Raising the efficiency ceiling of multi-junction solar cells (MJSCs) through the use of more optimal band gap configurations of next-generation MJSC is crucial for concentrator and space systems. Towards this goal, we propose two strain balanced multiple quantum well (SBMQW) structures to tune the bandgap of InGaP-based solar cells. These structures are based on InxGa1-xAs1-zPz/InyGa1-yP (x > y) and InxGa1-xP/InyGa1-yP (x > y) well/barrier combinations, lattice matched to GaAs in a p-i-n solar cell device. The bandgap of InxGa1-xAs1-zPz/InyGa1-yP can be tuned from 1.82 to 1.65 eV by adjusting the well composition and thickness, which promotes its use as an efficient subcell for next generation five and six junction photovoltaic devices. The thicknesses of wells and barriers are adjusted using a zero net stress balance model to prevent the formation of defects. Thin layers of InGaAsP wells have been grown thermodynamically stable with compositions within the miscibility gap for the bulk alloy. The growth conditions of the two SBMQWs and the individual layers are reported. The structures are characterized and analyzed by optical microscopy, X-ray diffraction, photoluminescence, current-voltage characteristics, and spectral response (external quantum efficiency). The effect of the well number on the excitonic absorption of InGaAsP/InGaP SBMQWs is discussed and analyzed.

  9. Improved interface quality and luminescence capability of InGaN/GaN quantum wells with Mg pretreatment

    NASA Astrophysics Data System (ADS)

    Wu, Zhengyuan; Shen, Xiyang; Xiong, Huan; Li, Qingfei; Kang, Junyong; Fang, Zhilai; Lin, Feng; Yang, Bilan; Lin, Shilin; Shen, Wenzhong; Zhang, Tong-Yi

    2016-02-01

    Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface. The indium in the Mg-pretreated InGaN layer was homogeneously distributed, making the interfaces abrupt. The improved interface quality greatly enhanced light emission capacity. The cathodoluminescence intensity of the Mg-pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment.

  10. Generation of coherent terahertz radiation by polarized electron-hole pairs in GaAs/AlGaAs quantum wells

    SciTech Connect

    Andrianov, A. V. Alekseev, P. S.; Klimko, G. V.; Ivanov, S. V.; Shcheglov, V. L.; Sedova, M. A.; Zakhar'in, A. O.

    2013-11-15

    The generation of coherent terahertz radiation upon the band-to-band femtosecond laser photoexcitation of GaAs/AlGaAs multiple-quantum-well structures in a transverse electric field at room temperature is investigated. The properties of the observed terahertz radiation suggest that it is generated on account of the excitation of a time-dependent dipole moment as a result of the polarization of nonequilibrium electron-hole pairs in quantum wells by the electric field. The proposed theoretical model taking into account the dynamic screening of the electric field in the quantum wells by nonequilibrium charge carriers describes the properties of the observed terahertz signal.

  11. Optically induced excitonic electroabsorption in a periodically delta-doped InGaAs/GaAs multiple quantum well structure

    NASA Technical Reports Server (NTRS)

    Larsson, A.; Maserjian, J.

    1991-01-01

    Large optically induced Stark shifts have been observed in a periodically delta-doped InGaAs/GaAs multiple quantum well structure. With an excitation intensity of 10 mW/sq cm, an absolute quantum well absorption change of 7000/cm was measured with a corresponding differential absorption change as high as 80 percent. The associated maximum change in the quantum well refractive index is 0.04. This material is promising for device development for all-optical computing and signal processing.

  12. Trap states in AlGaN channel high-electron-mobility transistors

    SciTech Connect

    Zhao, ShengLei; Zhang, Kai; Ha, Wei; Chen, YongHe; Zhang, Peng; Zhang, JinCheng; Hao, Yue; Ma, XiaoHua

    2013-11-18

    Frequency dependent capacitance and conductance measurements were performed to analyze the trap states in the AlGaN channel high-electron-mobility transistors (HEMTs). The trap state density in the AlGaN channel HEMTs decreases from 1.26 × 10{sup 13} cm{sup −2}eV{sup −1} at the energy of 0.33 eV to 4.35 × 10{sup 11} cm{sup −2}eV{sup −1} at 0.40 eV. Compared with GaN channel HEMTs, the trap states in the AlGaN channel HEMTs have deeper energy levels. The trap with deeper energy levels in the AlGaN channel HEMTs is another reason for the reduction of the reverse gate leakage current besides the higher Schottky barrier height.

  13. Polarization engineering of back-illuminated separate absorption and multiplication AlGaN avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Yang, Guofeng; Wang, Fuxue

    2016-08-01

    The back-illuminated separate absorption and multiplication AlGaN avalanche photodiodes (APDs) with a p-type graded AlGaN layer have been designed to investigate the polarization engineering on the performance of the devices. The calculated results show that the APD with p-graded AlGaN layer exhibits lower avalanche breakdown voltage and increased maximum multiplication gain compared to the structure with conventional p-type AlGaN layer. The improved performance of the designed APD is numerically explained by the polarization-assisted enhancement of the ionization electric field in the multiplication region and polarization doping effect caused by the p-type graded layer.

  14. Monitoring and Controlling of Strain During MOCVD of AlGaN for UV Optoelectronics

    SciTech Connect

    Han, J.; Crawford, M.H.; Shul, R.J.; Hearne, S.J.; Chason, E.; Figiel, J.J.; Banas, M.

    1999-01-14

    The grown-in tensile strain, due to a lattice mismatch between AlGaN and GaN, is responsible for the observed cracking that seriously limits the feasibility of nitride-based ultraviolet (UV) emitters. We report in-situ monitoring of strain/stress during MOCVD of AlGaN based on a wafer-curvature measurement technique. The strain/stress measurement confirms the presence of tensile strain during growth of AlGaN pseudomorphically on a thick GaN layer. Further growth leads to the onset of stress relief through crack generation. We find that the growth of AlGaN directly on low-temperature (LT) GaN or AlN buffer layers results in a reduced and possibly controllable strain.

  15. Strain-balanced InGaN/GaN multiple quantum wells

    SciTech Connect

    Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M.; Bharrat, D.; El-Masry, N. A.

    2014-07-21

    InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1−x}N/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1−y}N templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1−x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1−y}N template. Growth of the In{sub y}Ga{sub 1−y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1−y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1−x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1−y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”.

  16. 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

  17. Visualizing Non-abrupt Transition of Quantum Well States at Stepped Silver Surfaces

    PubMed Central

    Kumar Saha, Srijan; Manna, Sujit; Stepanyuk, Valeri S.; Kirschner, Jürgen

    2015-01-01

    We use scanning tunneling spectroscopy (STS) experiments and first-principles density functional theory (DFT) calculations to address a fundamental question of how quantum well (QW) states for electrons in a metal evolve spatially in the lateral direction when there is a surface step that changes the vertical confinement thickness. This study reveals a clear spatially dependent, nearly continuous trend in the energetic shifts of quantum well (QW) states of thin Ag(111) film grown on Cu(111) substrate, showing the strongest change near the step edge. A large energetic shift equaling up to ~200 meV with a lateral extension of the QW states of the order of ~20 Å is found, even though the step-edge is atomically sharp as evidenced by a line scan. The observed lateral extension and the nearly smooth transition of QW states are understood within the context of step-induced charge oscillation, and Smoluchowski-type charge spreading and smoothing. PMID:26243639

  18. Second harmonic generation from metamaterials strongly coupled to intersubband transitions in quantum wells

    SciTech Connect

    Campione, Salvatore; Benz, Alexander; Brener, Igal; Sinclair, Michael B.; Capolino, Filippo

    2014-03-31

    We theoretically analyze the second harmonic generation capacity of two-dimensional periodic metamaterials comprising sub-wavelength resonators strongly coupled to intersubband transitions in quantum wells (QWs) at mid-infrared frequencies. The metamaterial is designed to support a fundamental resonance at ∼30 THz and an orthogonally polarized resonance at the second harmonic frequency (∼60 THz), while the asymmetric quantum well structure is designed to provide a large second order susceptibility. Upon continuous wave illumination at the fundamental frequency we observe second harmonic signals in both the forward and backward directions, with the forward efficiency being larger. We calculate the overall second harmonic conversion efficiency of the forward wave to be ∼1.3 × 10{sup −2} W/W{sup 2}—a remarkably large value, given the deep sub-wavelength dimensions of the QW structure (about 1/15th of the free space wavelength of 10 μm). The results shown in this Letter provide a strategy for designing easily fabricated sources across the entire infrared spectrum through proper choice of QW and resonator designs.

  19. Recombination dynamics in InAsSb quantum-well diode lasers measured using photoluminescence upconversion

    NASA Astrophysics Data System (ADS)

    Cooley, W. T.; Hengehold, R. L.; Yeo, Y. K.; Turner, G. W.; Loehr, J. P.

    1998-11-01

    We report Shockley-Read-Hall (SRH), radiative, and Auger recombination rates in midinfrared laser structures from time-resolved photoluminescence using frequency upconversion. The devices studied were actual InAsSb/InAlAsSb multiple-quantum-well (MQW) diode lasers emitting near 3.3 μm, which have been previously characterized for laser performance. We extend the initial studies and report on the carrier recombination dynamics. The importance of carrier density motivates a careful examination of carrier density and quantum-well effects. SRH, radiative, and Auger recombination rates (ASRH, Brad, and CAuger, respectively) were measured at 77 K and found to be ASRH-1≈10 ns, Brad≈2×10-10 cm3 s-1, and CAuger⩽1.0×10-29 cm6 s-1, respectively. At 150 K the nonradiative recombination coefficients increased to ASRH-1≈1.7 ns, Brad≈0.78×10-10 cm3 s-1 and CAuger≈7.0×10-28 cm6 s-1, respectively. This study suggests InAsSb/InAlAsSb MQW diode laser performance may be limited by SRH nonradiative recombination mechanisms rather than Auger recombination.

  20. Strained layer InP/InGaAs quantum well laser

    NASA Technical Reports Server (NTRS)

    Forouhar, Siamak (Inventor); Larsson, Anders G. (Inventor); Ksendzov, Alexander (Inventor); Lang, Robert J. (Inventor)

    1993-01-01

    Strained layer single or multiple quantum well lasers include an InP substrate, a pair of lattice-matched InGaAsP quarternary layers epitaxially grown on the substrate surrounding a pair of lattice matched In.sub.0.53 Ga.sub.0.47 As ternary layers surrounding one or more strained active layers of epitaxially grown, lattice-mismatched In.sub.0.75 Ga.sub.0.25 As. The level of strain is selected to control the bandgap energy to produce laser output having a wavelength in the range of 1.6 to 2.5 .mu.m. The multiple quantum well structure uses between each active layer. Diethyl zinc is used for p-type dopant in an InP cladding layer at a concentration level in the range of about 5.times.10.sup.17 /cm.sup.3 to about 2.times.10.sup.18 /cm.sup.3. Hydrogen sulfide is used for n-type dopant in the substrate.

  1. Magnetotransport in p-type Ge quantum well narrow wire arrays

    SciTech Connect

    Newton, P. J. Llandro, J.; Mansell, R.; Barnes, C. H. W.; Holmes, S. N.; Morrison, C.; Foronda, J.; Myronov, M.; Leadley, D. R.

    2015-04-27

    We report magnetotransport measurements of a SiGe heterostructure containing a 20 nm p-Ge quantum well with a mobility of 800 000 cm{sup 2} V{sup −1} s{sup −1}. By dry etching arrays of wires with widths between 1.0 μm and 3.0 μm, we were able to measure the lateral depletion thickness, built-in potential, and the phase coherence length of the quantum well. Fourier analysis does not show any Rashba related spin-splitting despite clearly defined Shubnikov-de Haas oscillations being observed up to a filling factor of ν = 22. Exchange-enhanced spin-splitting is observed for filling factors below ν = 9. An analysis of boundary scattering effects indicates lateral depletion of the hole gas by 0.5 ± 0.1 μm from the etched germanium surface. The built-in potential is found to be 0.25 ± 0.04 V, presenting an energy barrier for lateral transport greater than the hole confinement energy. A large phase coherence length of 3.5 ± 0.5 μm is obtained in these wires at 1.7 K.

  2. Development and application of InAsP/InP quantum well infrared detector

    NASA Astrophysics Data System (ADS)

    Geetanjali, Porwal, S.; Kumar, R.; Dixit, V. K.; Sharma, T. K.; Oak, S. M.

    2016-05-01

    InAsxP1-x/InP quantum wells grown using metal organic vapor phase epitaxy are investigated for infrared detector applications. The structural parameters of the QWs are evaluated from high resolution x-ray diffraction. The electronic transition energies measured from surface photo voltage and photoconductivity confirms that these QWs can be used for fabricating IR detectors in the wide wavelength range, i.e. 0.9-1.46 µm by inter-band transitions and 7-18 µm by inter-sub-band transitions. Subsequently the functionality of one such fabricated InAsxP1-x/InPQW detector is verified by measuring the photoluminescence of suitable semiconductor quantum well structure. At the request of all authors of the paper, and with the agreement of the Proceedings Editor, an updated version of this article was published on 24 June 2016. The original version supplied to AIP Publishing contained an error in the Figures 1 and 2 where the right side of the images were cutoff. The error has been corrected in the updated and re-published article.

  3. Femtosecond cooling of hot electrons in CdSe quantum-well platelets.

    PubMed

    Sippel, Philipp; Albrecht, Wiebke; van der Bok, Johanna C; Van Dijk-Moes, Relinde J A; Hannappel, Thomas; Eichberger, Rainer; Vanmaekelbergh, Daniel

    2015-04-01

    Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well nanoplatelets using ultrafast two-photon photoemission spectroscopy at low excitation intensities, resulting typically in 1-5 hot electrons per platelet. We observe initial electron cooling in the femtosecond time domain that slows down with decreasing electron energy and is finished within 2 ps. The cooling is considerably faster at cryogenic temperatures than at room temperature, and at least for the systems that we studied, independent of the thickness of the platelets (here 3-5 CdSe units) and the presence of a CdS shell. The cooling rates that we observe are orders of magnitude faster than reported for similar CdSe platelets under strong excitation. Our results are understood by a classic cooling mechanism with emission of longitudinal optical phonons without a significant influence of the surface. PMID:25764379

  4. Optical gain in GaAsBi/GaAs quantum well diode lasers.

    PubMed

    Marko, Igor P; Broderick, Christopher A; Jin, Shirong; Ludewig, Peter; Stolz, Wolfgang; Volz, Kerstin; Rorison, Judy M; O'Reilly, Eoin P; Sweeney, Stephen J

    2016-07-01

    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.

  5. Composition modulation in GaInNAs quantum wells: Comparison of experiment and theory

    NASA Astrophysics Data System (ADS)

    Herrera, M.; González, D.; Hopkinson, M.; Gutiérrez, M.; Navaretti, P.; Liu, H. Y.; García, R.

    2005-04-01

    Composition modulation observed in GaInNAs quantum wells imposes an important handicap to their potential application within optical components, particularly as the indium and nitrogen contents are increased to reach longer wavelengths. In this paper, we compare our experimental results of phase separation in GaInNAs quantum wells grown at different temperatures with recent theoretical models of spinodal decomposition from the literature. This comparison has shown that the regular solution approximation, which explains the higher composition modulation compared to GaInAs samples, provides a more appropriate explanation of GaInNAs decomposition than the usual delta lattice-parameter approximation. Transmission electron microscopy shows no composition modulation contrasts with the chemical sensitive 002 dark field reflection and a strong increase in the intensity of the strain contrasts observed with 220 bright field reflection as the growth temperature increases from 360to460°C. These observations can be explained by an uncoupling between N and In composition profiles forming separate In-rich and N-rich regions according to the regular solution approximation model. We therefore believe that the compositional fluctuations in GaInNAs are not only due to GaInAs decomposition, but that an uncoupled modulation of the III and V elements is also present.

  6. Ge/SiGe quantum wells on Si(111): Growth, structural, and optical properties

    SciTech Connect

    Gatti, E. Pezzoli, F.; Grilli, E.; Isa, F.; Chrastina, D.; Isella, G.; Müller Gubler, E.

    2014-07-28

    The epitaxial growth of Ge/Si{sub 0.15}Ge{sub 0.85} multiple quantum wells (MQWs) on Si(111) substrates is demonstrated. A 3 μm thick reverse, double-step virtual substrate with a final composition of Si{sub 0.10}Ge{sub 0.90} has been employed. High resolution XRD, TEM, AFM and defect etching analysis has been used for the study of the structural properties of the buffer and of the QWs. The QW stack is characterized by a threading dislocation density of about 3 × 10{sup 7 }cm{sup −2} and an interdiffusion layer at the well/barrier interface of 2.1 nm. The quantum confined energy levels of this system have been calculated using the k·p and effective mass approximation methods. The Ge/Si{sub 0.15}Ge{sub 0.85} MQWs have been characterized through absorption and photoluminescence measurements. The optical spectra have been compared with those of Ge/Si{sub 0.15}Ge{sub 0.85} QWs grown on Si(001) through a thick graded virtual substrate.

  7. AC transport in p-Ge/GeSi quantum well in high magnetic fields

    SciTech Connect

    Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.; Golub, L. E.; Tarasenko, S. A.; Suslov, A. V.; Mironov, O. A.; Kummer, M.; Känel, H. von

    2014-08-20

    The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shown that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.

  8. Optical gain in GaAsBi/GaAs quantum well diode lasers.

    PubMed

    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

  9. Temperature engineered growth of low-threshold quantum well lasers by metalorganic chemical vapor deposition

    SciTech Connect

    Dzurko, K.M.; Menu, E.P.; Beyler, C.A.; Osinski, J.S.; Dapkus, P.D.

    1989-01-09

    A new technique is demonstrated for the formation of narrow active regions in quantum well lasers. In temperature engineered growth (TEG), the substrate temperature is varied during the growth of epitaxial layers by metalorganic chemical vapor deposition (MOCVD) on nonplanar substrates, allowing two-dimensional control of device features. Buried heterostructure designs with submicron active region stripe widths are obtained without the need for fine process control of lateral dimensions. The contact area above the active region is coplanar with the surrounding surface and wide enough to allow easy contacting and heat sinking. Carrier confinement is accomplished by lateral thickness variation of the quantum well active region resulting in a local strip of minimum band gap. Lasers grown in this manner exhibit cw threshold currents as low as 3.8 mA (3.4 mA pulsed), having an as-grown active region width of 0.5 ..mu..m. The near-field optical profile indicates stable, single transverse mode operation and minimal current leakage in these devices.

  10. Optical gain in GaAsBi/GaAs quantum well diode lasers

    NASA Astrophysics Data System (ADS)

    Marko, Igor P.; Broderick, Christopher A.; Jin, Shirong; Ludewig, Peter; Stolz, Wolfgang; Volz, Kerstin; Rorison, Judy M.; O’Reilly, Eoin P.; Sweeney, Stephen J.

    2016-07-01

    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.

  11. Effect of III-V on insulator structure on quantum well intermixing

    NASA Astrophysics Data System (ADS)

    Takashima, Seiya; Ikku, Yuki; Takenaka, Mitsuru; Takagi, Shinichi

    2016-04-01

    To achieve the monolithic active/passive integration on the III-V CMOS photonics platform, quantum well intermixing (QWI) on III-V on insulator (III-V-OI) is studied for fabricating multi-bandgap III-V-OI wafers. By optimizing the QWI condition for a 250-nm-thick III-V layer, which contains a five-layer InGaAsP-based multi-quantum well (MQW) with 80-nm-thick indium phosphide (InP) cladding layers, we have successfully achieved a photoluminescence (PL) peak shift of over 100 nm on the III-V-OI wafer. We have also found that the progress of QWI on the III-V-OI wafer is slower than that on the InP bulk wafer regardless of the buried oxide (BOX) thickness, bonding interface materials, and handle wafers. We have also found that the progress of QWI on the III-V-OI wafer is slower than that on the InP bulk wafer regardless of the buried oxide (BOX) thickness, bonding interface materials, and bulk support wafers on which the III-V-OI structure is formed (handle wafers). By comparing between the measured PL shift and simulated diffusions of phosphorus vacancies and interstitials during QWI, we have found that the slow QWI progress in the III-V-OI wafer is probably attributed to the enhanced recombination of vacancies and interstitials by the diffusion blocking of vacancies and interstitials at the BOX interface.

  12. Interband magneto-spectroscopy in InSb square and parabolic quantum wells

    SciTech Connect

    Kasturiarachchi, T.; Edirisooriya, M.; Mishima, T. D.; Doezema, R. E.; Santos, M. B.; Saha, D.; Pan, X.; Sanders, G. D.; Stanton, C. J.

    2015-06-07

    We measure the magneto-optical absorption due to intersubband optical transitions between conduction and valence subband Landau levels in InSb square and parabolic quantum wells. InSb has the narrowest band gap (0.24 eV at low temperature) of the III–V semiconductors leading to a small effective mass (0.014 m{sub 0}) and a large g–factor (−51). As a result, the Landau level spacing is large at relatively small magnetic fields (<8 T), and one can observe spin-splitting of the Landau levels. We examine two structures: (i) a multiple-square-well structure and (ii) a structure containing multiple parabolic wells. The energies and intensities of the strongest features are well explained by a modified Pidgeon-Brown model based on an 8-band k•p model that explicitly incorporates pseudomorphic strain. The strain is essential for obtaining agreement between theory and experiment. While modeling the square well is relatively straight-forward, the parabolic well consists of 43 different layers of various thickness to approximate a parabolic potential. Agreement between theory and experiment for the parabolic well validates the applicability of the model to complicated structures, which demonstrates the robustness of our model and confirms its relevance for developing electronic and spintronic devices that seek to exploit the properties of the InSb band structure.

  13. Intersubband transitions in InGaAsN/GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Liu, W.; Zhang, D. H.; Fan, W. J.; Hou, X. Y.; Jiang, Z. M.

    2008-09-01

    The dependences of intersubband transitions on well width and nitrogen (N) content in n-type In0.23Ga0.77As1-xNx/GaAs quantum wells (QWs) are investigated using a ten-band k ṡp model. The absorption peak energy is found to increase first with the well width starting from 2 nm. It becomes insensitive from about 2.5 to 4.5 nm although the absorption intensity increases and bandwidth decreases monotonically, and then keeps decreasing with the well width beyond 4.5 nm. The peak energy is much larger than that of the N-free structure for narrower wells, but the difference decreases quickly with increasing well width. In the case of wider wells, the absorption peak energy shows relatively slow monotonic increase with increasing N content up to 3% because of the N-band and conduction-band coupling. In the nearly lattice-matched GaAsN/AlGaAs QWs the absorption peak energy shows a redshift with increasing N content from 0% to 0.4% and then increases gradually. The theoretical results are consistent with the reported experimental data.

  14. Magnetotransport in double quantum well with inverted energy spectrum: HgTe/CdHgTe

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Suslov, A. V.; Popov, M. R.; Novik, E. G.; Dvoretsky, S. A.; Mikhailov, N. N.

    2016-02-01

    We present an experimental study of the double-quantum-well (DQW) system made of two-dimensional layers with inverted energy band spectrum: HgTe. The magnetotransport reveals a considerably larger overlap of the conduction and valence subbands than in known HgTe single quantum wells (QW), which may be regulated here by an applied gate voltage Vg. This large overlap manifests itself in a much higher critical field Bc separating the range above it with a plain behavior of the Hall magnetoresistance ρx y(B ) , where the quantum peculiarities shift linearly with Vg, and the range below with a complicated behavior. In the latter case, specific structures in ρx y(B ) are formed like a double-N -shaped ρx y(B ) , reentrant sign-alternating quantum Hall effect with transitions into a zero-filling-factor state, etc., which are clearly manifested here due to better magnetic quantization at high fields, as compared to the features seen earlier in a single HgTe QW. The coexisting electrons and holes were found in the whole investigated range of positive and negative Vg as revealed (i) from fits to the low-field N -shaped ρx y(B ) , (ii) from the Fourier analysis of oscillations in ρx x(B ) , and (iii) from a specific behavior of ρx y(B ) at high positive Vg. A peculiar feature here is that the found electron density n remains almost constant in the whole range of investigated Vg while the hole density p drops down from the value a factor of 6 larger than n at extreme negative Vg to almost zero at extreme positive Vg passing through the charge-neutrality point. We show that this difference between n and p stems from an order of magnitude larger density of states for holes in the lateral valence subband maxima than for electrons in the conduction subband minimum. We analyze our observations on the basis of a calculated picture of magnetic levels in a DQW and suggest that their specificity is due to (i) a nonmonotonic course of the valence subband magnetic levels and an

  15. Exciton binding energies and absorption in intermixed GaAs-AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Meney, Alistair T.

    1992-12-01

    The optical properties of excitons in layer-intermixed GaAs-AlGaAs quantum wells are studied theoretically. The electronic dispersion is obtained using the 6×6 Luttinger-Kohn Hamiltonian for the valence bands, and an accurate expression for the conduction band dispersion which includes the effects of nonparabolicity and warping to fourth order in k. The HH1-CB1 (1s) and LH1-CB1(1s) exciton binding energies are calculated as a function of diffusion time. The absorption for both TE and TM polarization is obtained at several wavelengths, and is seen to decrease significantly with increased intermixing. The decrease in absorption is larger for narrow wells, where the effects of intermixing are more pronounced for a given diffusion time.

  16. Superconducting proximity effect in inverted InAs/GaSb quantum well structures with Ta electrodes

    NASA Astrophysics Data System (ADS)

    Yu, Wenlong; Jiang, Yuxuan; Huan, Chao; Chen, Xunchi; Jiang, Zhigang; Hawkins, Samuel D.; Klem, John F.; Pan, Wei

    2014-11-01

    We present our recent electronic transport results in top-gated InAs/GaSb quantum well hybrid structures with superconducting Ta electrodes. We show that the transport across the InAs-Ta junction depends largely on the interfacial transparency, exhibiting distinct zero-bias behavior. For a relatively resistive interface, a broad conductance peak is observed at zero bias. When a transparent InAs-Ta interface is achieved, a zero-bias conductance dip appears with two coherent-peak-like features forming at bias voltages corresponding to the superconducting gap of Ta. The conductance spectra of the transparent InAs-Ta junction at different gate voltages can be fit well using the standard Blonder-Tinkham-Klapwijk theory.

  17. Pseudomorphic GeSn/Ge(001) quantum wells: Examining indirect band gap bowing

    SciTech Connect

    Tonkikh, Alexander A.; Eisenschmidt, Christian; Schmidt, Georg; Talalaev, Vadim G.; Zakharov, Nikolay D.; Werner, Peter; Schilling, Joerg

    2013-07-15

    A study of the bandgap character of compressively strained GeSn{sub 0.060-0.091}/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and {Gamma} conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, b{sub L} = 0.80 {+-} 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

  18. Room temperature spin transport in undoped (110) GaAs/AlGaAs quantum wells

    SciTech Connect

    Yokota, Nobuhide Aoshima, Yohei; Ikeda, Kazuhiro; Kawaguchi, Hitoshi

    2014-02-17

    We are reporting on our first observation of a micrometer-order electron spin transport in a (110) GaAs/AlGaAs multiple quantum well (QW) at room temperature using a space- and time-resolved Kerr rotation technique. A 37-μm transport was observed within an electron spin lifetime of 1.2 ns at room temperature when using an in-plane electric field of 1.75 kV/cm. The spatio-temporal profiles of electron spins were well reproduced by the spin drift-diffusion equations coupled with the Poisson equation, supporting the validity of the measurement. The results suggest that (110) QWs are useful as a spin transport layer for semiconductor spintronic devices operating at room temperature.

  19. Enhancement of coherent acoustic phonons in InGaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Hafiz, Shopan D.; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

    2015-03-01

    Enhancement of coherent zone folded longitudinal acoustic phonon (ZFLAP) oscillations at terahertz frequencies was demonstrated in InGaN multiple quantum wells (MQWs) by using wavelength degenerate time resolved differential transmission spectroscopy. Screening of the piezoelectric field in InGaN MQWs by photogenerated carriers upon femtosecond pulse excitation gave rise to terahertz ZFLAPs, which were monitored at the Brillouin zone center in the transmission geometry. MQWs composed of 10 pairs InxGa1-xN wells and In0.03Ga0.97N barriers provided coherent phonon frequencies of 0.69-0.80 THz depending on the period of MQWs. Dependences of ZFLAP amplitude on excitation density and wavelength were also investigated. Possibility of achieving phonon cavity, incorporating a MQW placed between two AlN/GaN phonon mirrors designed to exhibit large acoustic gaps at the zone center, was also explored.

  20. Influence of AlN thickness on AlGaN epilayer grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jayasakthi, M.; Juillaguet, S.; Peyre, H.; Konczewicz, L.; Baskar, K.; Contreras, S.

    2016-10-01

    AlGaN/AlN layers were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The AlN buffer thickness was varied from 400 nm to 800 nm. The AlGaN layer thickness was 1000 nm. The crystalline quality, thickness and composition of AlGaN were determined using high resolution X-ray diffraction (HRXRD). The threading dislocation density (TDD) was found to decrease with increase of AlN layer thickness. Reciprocal space mapping (RSM) was used to estimate the strain and relaxation between AlGaN and AlN. The optical properties of AlGaN layers were investigated by temperature dependent photoluminescence (PL). PL intensities of AlGaN layers increases with increasing the AlN thickness. The surface morphology of AlGaN was studied by atomic force microscopy (AFM). Root mean square (RMS) roughness values were found to be decreased while increase of AlN thickness.