Population inversion between Γ subbands in quantum wells under the conditions of Γ-<Emphasis Type="Italic">L</Emphasis> intervalley transfer

Monte Carlo simulations of electron transport in Al_xGa_1−x As/GaAs/In_yGa_1−y As double-quantum-well heterostructures in high lateral electric fields are carried out. It is shown that, under the conditions of intervalley Γ-L electron transfer, there exists a population inversion between the first and the second quantum-confinement subbands in the Γ valley. The population inversion appears in the fields exceeding 4 and 5.5 kV/cm at 77 and 300 K, respectively. The gain in a superlattice composed of such quantum wells is estimated to be on the order of 100 cm⁻¹ for radiation with a wavelength of 12.6 μm. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 2, 2003, pp. 224–229. Original Russian Text Copyright ? 2003 by Aleshkin, Andronov, Dubinov.     

Tuning the energy spectrum of InAs/GaAs quantum dots by varying the thickness and composition of the thin double GaAs/InGaAs cladding layer

It is shown that the ground state transition energy in quantum dots in heterostructures grown by atmospheric-pressure MOCVD can be tuned in the range covering both transparence windows of the optical fiber at wavelengths of 1.3 and 1.55 μm by varying the thickness and composition of the thin GaAs/In_xGa_1−x As double cladding layer. These structures also exhibit a red shift of the ground state transition energy of the In_xGa_1−x As quantum well (QW) as a result of the formation of a hybrid QW In_xGa_1−x As/InAs (wetting layer) between the quantum dots (QDs). The Schottky diodes based on these structures are characterized by an increased reverse current, which is attributed to thermally activated tunneling of electrons from the metal contact to QD levels. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 448–454. Original Russian Text Copyright ? 2004 by Karpovich, Zvonkov, Levichev, Baidus, Tikhov, Filatov, Gorshkov, Ermakov.     

Inversion of the electron population in subbands of dimensional quantization with longitudinal transport in tunnel-coupled quantum wells

The scheme of a laser which can operate in the far-infrared range (λ ∼ 150 μm) is suggested. In order to attain the inversion of the subband population it was suggested that electron transport in three tunnel-coupled quantum wells in a strong electric field, which lies in the plane of quantum wells, be used. An important specific feature of the structure suggested is the presence of a single rough heterointerface. The electron trans-port was simulated by the Monte Carlo method for the Al_xGa_1−x As/GaAs (x=0.2–0.3) heterostructure. The simulation demonstrated that the population inversion in the first and second subbands of dimensional quantization is realized in the field above 1.2 kV/cm at T=4.2 and 77 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 6, 2002, pp. 724–729. Original Russian Text Copyright ? 2002 by Aleshkin, Dubinov.     

A graded-gap detector of ionizing radiation

The current response of Al_xGa_1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick Al_xGa_1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of Al_xGa_1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap Al_xGa_1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×10³ V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.     

Long-wavelength photodiodes based on Ga1−x InxAsySb1−y wit composition near the miscibility boundary

The possibility of using liquid-phase epitaxy to obtain Ga_1−x In_xAs_ySb_1−y solid solutions isoperiodic with GaSb near the miscibility boundary is investigated. The effect of crystallographic orientation of the substrate on the composition of the solid solutions grown in this way is examined, and the indium concentration is observed to grow from 0.215 to 0.238 in the Ga_1−x In_xAs_ySb_1−y solid phase in the series of substrate orientations (100), (111)A, (111)B. A change in the composition of the solid solution leads to a shift of the long-wavelength edge of the spectral distribution of the photosensitivity. The use of a GaSb (111)B substrate made it possible, without lowering the epitaxy temperature, to increase the indium content in the solid phase to 23.8% and to create long-wavelength photodiodes with spectral photosensitivity threshold λ _th=2.55 μm. The primary characteristics of such photodiodes are described, along with aspects of their fabrication. The proposed fabrication technique shows potential for building optoelectronic devices (lasers, LED’s, photodiodes) based on Ga_1−x In_xAs_ySb_1−y solid solutions with red boundary as high as 2.7 μm. Fiz. Tekh. Poluprovodn. 33, 249–253 (February 1999)     

Influence of the variband-layer thickness on the energy and frequency characteristics of In x(z)Ga1 − x(z)As Gunn diodes

The operation of variband-In _x(z)Ga_{1 − x(z)}As Gunn diodes with an active-region length of 2.5 μm and an n ⁺-n cathode contact is studied by using a two-temperature model of electron intervalley transfer in a varib-and semiconductor. It is established that, in diodes, dipole domains or accumulation layers may be formed depending on the variband-layer thickness. The use of variband In _x(z)Ga_{1 − x(z)}As in the active region with an appropriate variband-layer thickness allows one to enhance the output power and the generation efficiency by a factor of approximately 1.5 and to increase the width of the frequency range of the diode operation approximately twofold as compared to that of an In_0.2Ga_0.8As-based diode. Original Russian Text ? Yu.V. Arkusha, E.D. Prokhorov, I.P. Storozhenko, 2006, published in Radiotekhnika i Elektronika, 2006, Vol. 51, No. 3, pp. 371–378.     

Analysis of mechanisms for electron scattering in GaAs/AlxGa1−x As superlattices with doped quantum wells for longitudinal resonant current flow in high electric fields and at low temperatures

Formulas are derived for, and a numerical analysis made of, the dependence of the transverse phase relaxation time on electron energy for resonant current flow through GaAs/Al_xGa_1−x As superlattices with doped quantum wells. The parameters are chosen to be close to those of superlattices used for creating photodiodes for operation at λ⋍10 μm. The analysis is limited to the interactions of electrons with neutral atoms and impurity ions at low temperatures. Resonant current flow is ensured by an electric field that brings the ground state and the first excited state of the “Stark ladder” into resonance with neighboring, weakly interacting quantum wells. Fiz. Tekh. Poluprovodn. 33, 438–444 (April 1999)     

Luminescence and electrical properties of InGaN/AlGaN/GaN light emitting diodes with multiple quantum wells

Luminescence spectra of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells are studied for currents in the range J=0.15 μA-150 mA. The comparatively high quantum efficiency for low J(J _max=0.5–1 mA) is a consequence of a low probability for the nonradiative tunnel current. The current-voltage characteristics J(V) are studied for J=10⁻¹²–10⁻¹ A; they are approximated by the function V=ϕk+mkT· [1n(J/J ₀)+(J/J ₁)^0.5] + J · R _s. The portion of V∞(J/J ₁)^0.5 and measurements of the dynamic capacitance indicate that i-layers adjacent to the active layer play an important role. The spectra are described by a model with a two-dimensional density of states with exponential tails in multiple quantum wells. The rise in T with increasing J is determined from the short-wavelength decay of the spectrum of the blue diodes: T=360–370 K for J=80–100 mA. An emission band is observed at 2.7–2.8 eV from green diodes at high J; this band may be explained by phase separation with different amounts of In in the InGaN. Fiz. Tekh. Poluprovodn. 33, 445–450 (April 1999)     

Room temperature λ=1.3 µm photoluminescence from InGaAs quantum dots on (001) Si substrate

GaAs/In_xGa_1−x As quantum dot heterostructures exhibiting high-intensity λ=1.3 μm photoluminescence at room temperature have been grown on (001) Si substrate with a Si_1−x Ge_x buffer layer. The growth was done successively on two MBE machines with sample transfer via the atmosphere. The results obtained by the study of the structure growth process by means of high-energy electron diffraction are presented. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 5, 2002, pp. 565–568. Original Russian Text Copyright ? 2002 by Burbaev, Kazakov, Kurbatov, Rzaev, Tsvetkov, Tsekhosh.     

High density 2DEG in III-V semiconductor heterostructures and high-electron-mobility transistors based on them

Situation in high-electron-mobility transistor (HEMT) technology is discussed. The N-AlGaAs/InGaAs/GaAs pseudomorphic HEMT’s are now considered as most advanced for mmwave monolithic circuits, but metamorphic N-In_xAl_1−x As/In_yGa_1−y As/In_xAl_1−x As HEMT’s grown on GaAs substrates are very promising for the future high-frequency devices. High density 2DEG in HEMT’s is analyzed by means of the Hall effect and photoluminescence measurements. Processing technology of the sub-0.25-μm pseudomorphic HEMT’s, metamorphic HEMT’s and their characteristics are also described. Fiz. Tekh. Poluprovodn. 33, 1064–1065 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Molecular beam epitaxial growth of InGaAsSb on (100) GaSb with emission wavelength in the 2 to 2.5 μm range

Molecular beam epitaxial growth ofIn _x Ga _1−x As _y Sb _1−y lattice-matched to (100) GaSb substrate withx up to 0.26 is reported.As ₂ andSb ₂ sources were used and growth was studied in the temperature range of 490° C ∼ 570° C. Alloys with room temperature photoluminescence peak wavelengths as long as 2.5 μ have been grown with specular morphology. The low temperature photoluminescence of In_0.26Ga_0.74As_0.19Sb_0.81 measured at 1.8 K has a narrow peak at 2.23 μm with a full width at half maximum of 10 meV. This composition is inside the miscibility gap. These results indicate that metastable InGaAsSb alloys with optical device quality can be grown by molecular beam epitaxy.     

Photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures

An increase in the dark current (by 2–3 orders of magnitude) in GaAs/Al_xGa_1−x As multilayer quantum-well structures with x⋍0.4 is observed after illumination of the structures with optical light (λ<1.3 μm). This increase is sustained for an extended time (more than 10³ s) at low temperatures. It then decreases to its initial value upon heating of the sample. A model of the barrier with local sag of the conduction band facilitating tunneling is proposed. The conduction band sag and the magnitude of the current grow due to optical ionization of uncontrolled deep level clusters present in the barrier and decrease due to subsequent capture of electrons from the conduction band by the deep levels upon heating. Fiz. Tekh. Poluprovodn. 32, 209–214 (February 1998)     

Effect of successive implantation of Ag+(Cu+) and Xe+ ions on the recombination properties of CdxHg1−x Te crystals

The effect of successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions on the recombination properties of Cd_xHg_1−x Te (0.2<x<0.3) crystals has been investigated. It is shown that after implantation of ions of one chemical element, followed by diffusion thermal annealing at temperatures below 150–200 K, recombination through local levels lying 30±5 meV below the conduction band bottom dominates. Successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions followed by diffusion thermal annealing changes the course of the temperature dependence of the lifetime of the nonequilibrium charge carriers. It was determined that for Cd_xHg_1−x Te crystals with x⋍0.20–0.25 in the temperature interval 700–200 K the lifetime of the nonequilibrium charge carriers is low (τ<0.15 μs) and does not depend on the temperature. For Cd_xHg_1−x Te crystals with x⋍0.3 recombination of nonequilibrium charge carriers occurs through two types of levels: in the temperature range 140–200 K — deep levels E _t1⋍E _c −51 meV and at lower temperatures (77–140 K) — through shallower levels E _t2⋍E _c −(16±2) meV. Fiz. Tekh. Poluprovodn. 31, 786–789 (July 1997)     

Arrays of 128×128 photodetectors based on HgCdTe layers and multilayer heterostructures with GaAs/AlGaAs quantum wells

A technology has been elaborated and photodetector modules based on Hg_1−x Cd_xTe/GaAs heterostructures and GaAs/AlGaAs multiquantum-well structures grown by molecular-beam epitaxy were fabricated for the 3–5 and 8–12 μm spectral ranges. The photosensitive HgCdTe layers were grown on the GaAs substrates with the intermediate buffer layer of CdZnTe. To decrease the surface effect on the recombination processes, the graded-gap Hg_1−x Cd_xTe layers with x increasing towards the surface were grown. A silicon multiplexer was designed and fabricated by CMOS/CCD technology with a frame rate of 50 Hz. The hybrid microassembly of the photodetector array and the multiplexer was produced by group cold welding on indium columns while monitoring the connection process. The fabricated 128×128 modules based on HgCdTe layers with the cutoff wavelengths 6 and 8.7 μm had a temperature resolution of 0.02 K and 0.032 K, respectively, at a temperature of 78 K and a frame rate of 50 Hz. The photosensitive GaAs/AlGaAs multilayer quantum well structures were fabricated by MBE. It is shown that the technology developed allows 128×128 multielement photodetector arrays (λ_peak=8 μm) to be produced with a temperature resolution of 0.021 K and 0.06 K at operating temperatures of 54 K and 65 K, respectively. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 9, 2001, pp. 1159–1166. Original Russian Text Copyright ? 2001 by Ovsyuk, Sidorov, Vasil’ev, Shashkin.     

Photosensitivity of thin-film structures based on (CuInSe2)x(2ZnSe)1−x solid solutions

Polycrystalline (CuInSe₂)_x(2ZnSe)_1−x films (x=0.6–1.0) with p-type conductivity and a thickness of 0.5–0.9 μm were obtained by pulsed laser evaporation. It is shown that a chalcopyrite-sphalerite transition occurs in the above system for x=0.7. The obtained films were used to fabricate the photosensitive structure of the In/p-(CuInSe₂)_x(2ZnSe)_1−x and InSe(GaSe)/(CuInSe₂)_x(2ZnSe)_1−x types. Spectral dependences of photovoltaic-conversion quantum efficiency were studied, and the photosensitivity of the structures in relation to the type of energy barrier and the composition was analyzed. It is concluded that the structures under consideration can be used as broadband photovoltaic converters. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 576–581. Original Russian Text Copyright ? 2000 by V. Rud’, Yu. Rud’, Bekimbetov, Gremenok, Bodnar’, Rusak.     

Self-organized nanoscale InP islands in an InGaP/GaAs host and InAs islands in an InGaAs/InP host

Arrays of strained nanoscale InP islands in an In_0.49Ga_0.51P host on a GaAs(100) substrate and InAs islands in a In_0.53Ga_0.47As host on an InP(100) substrate are obtained by metalorganic vapor-phase epitaxy (MOVPE). Their structural and photoluminescence properties are investigated. It is shown that the nanoscale islands that are formed measure 80 nm (InP/InGaP) and 25–60 nm (InAs/InGaAs). The photoluminescence spectra of the nanoscale islands display bands in the wavelength ranges 0.66–0.72 and 1.66–1.91 μm at 77 K with maxima whose position does not vary as the effective thickness of InP and InAs increases. The radiation efficiency of the nanoscale InP islands is two orders of magnitude greater than the luminescence intensity of the InAs islands. Fiz. Tekh. Poluprovodn. 33, 858–862 (July 1999)     

AlGaInAs/InP strained-layer quantum well lasers at 1.3 µm grown by solid source molecular beam epitaxy

Al_xGa_yIn_1−x−yAs/InP strained-layer multiple-quantum-well lasers emitting at 1.3 μm have been grown by solid source molecular beam epitaxy, and the performance characteristics have been studied. The lasers contain 4, 5, or 6 compressively strained quantum wells in the active region. They exhibit low transparency current densities, high gain coefficients, and high characteristic temperatures compared to conventional GaInAsP/InP quantum well lasers. The results show that desired lasing features can be achieved with relatively simple layer structures if the doping profiles and waveguide structures are properly designed and the material is grown to high structural perfection.     

Optical properties of crystals of the solid solutions (InSb)1−x (CdTe)x

The reflection and absorption spectra of crystals of the solid solutions (InSb)_1−x (CdTe)_x in the wavelength interval 2.5–25 μm were measured within the limits of solubility of CdTe in InSb (x⩽0.05) at room temperature. Analysis of the experimental results confirmed the applicability of the Kane theory for all compositions investigated. The variation of the optical band gap ɛ _g ^opt and the effective mass m _c at the Fermi level as a function of composition was determined. It is shown that the minimum values m _c=0.8×10⁻² m ₀ and ɛ _g ^opt =0.07 eV are reached for x=0.02–0.03. Information about the predominant mechanism of scattering for each alloy is obtained from the absorption curves in the region of absorption by free charge carriers. X-Ray crystallographic investigations were performed and the change Δa(x) in the lattice constant of the solid solutions relative to pure InSb was determined. It is shown that the behavior of m _c(x) and ɛ _g ^opt is uniquely determined by Δa(x). In turn, Δa(x) is determined by the complicated character of the interaction of the dopants with one another and with the InSb lattice. Fiz. Tekh. Poluprovodn. 32, 303–306 (March 1998)     

Recombination mechanisms in doped n-type Hg1−x CdxTe crystals and properties of diffusion p +-n junctions based on them

We made p ⁺-n-type photodiodes for the 3–5 and 8–12 μm wavelength regions by diffusing As into single-crystal n-Hg_1−x Cd_xTe substrates, and investigated their electrical and photoelectric properties. Analysis of the temperature dependences of the differential resistance and current-voltage characteristics led us to conclude that charge-carrier transport is predominately due to the generation-recombination mechanism at a temperature of 77 K. As the temperature increases, a contribution from the diffusion component also appears. We obtained values of the product R ₀ A≅0.3–1.0, 1–10, and (1–10)×10⁴ Ω · cm² for diodes with long-wavelength photosensitivity cutoffs λ_c≅11.5, 10.5, and 6.0 μm, respectively, indicating that they could operate in the regime where performance is limited by background radiation fluctuations. Fiz. Tekh. Poluprovodn. 31, 350–354 (March 1997)     

Optical absorption by transitions between subbands of light and heavy holes in <Emphasis Type="Italic">p</Emphasis>-Mn<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

Absorption spectra of p-Mn_xHg_1−x Te epitaxial films with x=0.12–0.19 in the wavelength range of 2–24 μm at 300 and 80 K were measured. The absorption caused by transitions of charge carriers between subbands of light and heavy holes is calculated according to Kane’s theory taking into account the effect of remote bands. The values of the effective masses of heavy and light holes are obtained as functions of solid-solution composition and temperature. The analysis of low-temperature absorption spectra was carried out; the ionization energy of the acceptor level is evaluated. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 49–51. Original Russian Text Copyright ? 2002 by Nesmelova, Baryshev, Andreev. Deceased.