Special features of spontaneous and coherent emission of IR lasers based on a single type-II broken-gap heterojunction

The electroluminescence characteristics of a single type-II p-Ga_0.84In_0.16As_0.22Sb_0.78/n-In_0.83Ga_0.17As_0.80Sb_0.20 heterostructure have been studied in the temperature range 77–300 K. A new advanced laser structure based on a type-II broken-gap p-GaInAsSb/n-InGaAsSb heterojunction as the active region has been suggested and fabricated. Single-mode lasing at wavelength λ=3.14 µm under a threshold current density j_th=400 A/cm² (T=77 K) was obtained. The domination of TM-over TE-polarization, observed both in the spontaneous and coherent modes of operation of the novel laser structure, can be accounted for by involvement of light holes, tunneling across the heterointerface, in radiative recombination.     

Type II broken-gap GaSb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As<Emphasis Type="Italic">x</Emphasis>/InAs heterojunction (<Emphasis Type="Italic">x</Emphasis> < 0.15): Evolution of the band diagram for the ternary solid solution

Layers of the GaSb_{1 ? x} As _x alloy with arsenic content in the range x = 0.06–0.15 have been grown for the first time on InAs (100) substrates by metal-organic vapor-phase epitaxy. A new approach to the calculation of the band diagram of the GaSbAs alloy is suggested. It is demonstrated on the basis of magnetotransport measurements in p-GaSbAs/p-InAs heterostructures and with the method suggested by the authors for the calculation of band diagrams for alloys in the GaSbAs system that, in the composition range under study, the GaSbAs/InAs heterojunction is a type II broken-gap heterojunction.     

Interaction of charge carriers with the localized magnetic moments of manganese atoms in <Emphasis Type="Italic">p</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-InAs:Mn heterostructures

Transport properties of p-Ga_1?xIn_xAs_ySb_1?y/p-InAs:Mn heterostructures with undoped layers of solid solutions similar in composition to GaSb (x?0.22) grown by liquid-phase epitaxy on substrates with a Mn concentration of (5–7)×10¹⁸ cm^?3 are studied. It is ascertained that there is an electron channel at the interface (from the InAs side). The anomalous Hall effect and negative magnetoresistance are observed at relatively high temperatures (77–200) K. These phenomena can be attributed to the s-d-exchange interaction between Mn ions of the substrate and s electrons of the two-dimensional channel. The effective magnetic moment of Mn ions was evaluated as μ=200µ_B at T=77 K.     

Magnetotransport properties of type II heterojunctions based on GaInAsSb/InAs and GaInAsSb/GaSb

The results of detailed study of the magnetotransport properties of broken-gap type II heterojunctions in a GaInAsSb/InAs(GaSb) system are reported. An electron channel with a high charge-carrier mobility (as high as 50000–60000 cm²/(V s)) is observed and studied for the first time in an isotype broken-gap p-GaInAsSb/p-InAs heterostructure. The effects of electron-channel depletion and semimetal-semiconductor transition in the case of heavy doping of the quaternary alloy with acceptors are studied. Magnetotransport properties at temperatures of 4.2–200 K are studied in detail. Data on the energy spectrum and parameters of two-dimensional charge carriers at the heteroboundary are obtained. It is ascertained experimentally that, depending on the composition, either staggered (at x = 0.85) or broken-gap (at x = 0.95) heterojunctions can be formed in the Ga_1?x In_xAs_ySb_1?y /GaSb, which is confirmed by theoretical calculations. The anomalous Hall effect and negative magnetoresistance were observed in GaInAsSb/InAs:Mn grown on substrates doped heavily with Mn magnetic acceptor impurity so that the hole concentration was as high as p > 5 × 10¹⁸ cm^?3; these phenomena are caused by exchange interaction of Mn ions in InAs with high-mobility charge carriers in the electron channel at the heterointerface.     

Luminescence of multilayer structures based on InAsSb at λ = 6−9 μm

Multilayer gradient InAs_1?xSb_x/…/InAs_1?x?ySb_xP_y/n-InAs structures emitting in a wavelength range of 6 to 9 μm during injection, extraction, and optical pumping were studied.     

Influence of Composition on the Thermoelectric Properties of Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Thin Films

Bi_1?x Sb _x solid solutions have attracted much attention as promising thermoelectric (TE) materials for cooling devices at temperatures below ～200 K and as unique model materials for solid-state science because of a high sensitivity of their band structure to changes in composition, temperature, pressure, etc. Earlier, we revealed a non-monotonic behavior of the concentration dependences of TE properties for polycrystalline Bi_1?x Sb _x solid solutions and attributed these anomalies to percolation effects in the solid solution, transition to a gapless state, and to a semimetal–semiconductor transition. The goal of the present work is to find out whether the non-monotonic behavior of the concentration dependences of TE properties is observed in the thin film state as well. The objects of the study are Bi_1?x Sb _x thin films with thicknesses in the range d = 250–300 nm prepared by thermal evaporation of Bi_1?x Sb _x crystals (x = 0–0.09) onto mica substrates. It was shown that the anomalies in the dependence of the TE properties on Bi_1?x Sb _x crystal composition are reproduced in thin films.     

Comparative analysis of the mechanisms of interface formation in a film structure under equilibrium and strongly nonequilibrium condition

Structural (X-ray and electron diffraction) investigations of the interface in films of (Zn _{1 ? x} Cd _x Te) _{1 ? y} (In₂Te₃) _y alloys and zinc selenide grown on glass substrates under strongly nonequilibrium (substrate temperature T _s = 200 K) and quasi-equilibrium (T _s = 473 K) conditions have been performed. It is shown that growth of alloy films occurs through formation of nuclei of different shape and orientation. It is established that the alloy films grown on a cooled substrate have better (with respect to crystalline orientation) structural quality in comparison with similar films grown on a heated substrate, where Ostwald ripening plays an important role during growth.     

Resonant Raman scattering and atomic force microscopy of InGaAs/GaAs multilayer nanostructures with quantum dots

The transition from two-dimensional (2D) pseudomorphic growth to the three-dimensional (3D) (nanoisland) growth in In_xGa_1?xAs/GaAs multilayer structures grown by molecular-beam epitaxy was investigated by atomic force microscopy, photoluminescence, and Raman scattering. The nominal In content x in In_xGa_1?xAs was varied from 0.20 to 0.50. The thicknesses of the deposited In_xGa_1?xAs and GaAs layers were 14 and 70 monolayers, respectively. It is shown that, at these thicknesses, the 2D-3D transition occurs at x ≥ 0.27. It is ascertained that the formation of quantum dots (nanoislands) does not follow the classical Stranski-Krastanov mechanism but is significantly modified by the processes of vertical segregation of In atoms and interdiffusion of Ga atoms. As a result, the In_xGa_1?xAs layer can be modeled by a 2D layer with a low In content (x < 0.20), which undergoes a transition into a thin layer containing nanoislands enriched with In (x > 0.60). For multilayer In_xGa_1?xAs structures, lateral alignment of quantum dots into chains oriented along the \([\overline 1 10]\) direction can be implemented and the homogeneity of the sizes of quantum dots can be improved.     

High-efficiency dual-junction GaInP/GaAs tandem solar cells obtained by the method of MOCVD

Monolithic dual-junction GaInP/GaAs solar cells grown by the MOCVD method were studied. The conditions of the growth of ternary Ga _x In_1?x P and Al _x In_1?x P alloys lattice-matched to GaAs are optimized. Technology for fabrication of a tunneling diode with a high peak current density of 207 A/cm² on the basis of heavily doped n ⁺⁺-GaAs:Si and p ⁺⁺-AlGaAs:C layers is developed. Cascade GaInP/GaAs solar cells obtained as a result of relevant studies featuring a good efficiency of the solar-energy conversion both for space and terrestrial applications. The maximum value of the GaInP/GaAs solar-cell efficiency was 30.03% (at AM1.5D, 40 suns).     

The electrical and optical properties of InAs irradiated with electrons (∼2 MeV): The energy structure of intrinsic point defects

The results of experimental studies of the electrical and optical properties of n-and p-InAs crystals irradiated with electrons at an energy of ～2 MeV and doses as high as D = 1 × 10¹⁹ cm^?2 are reported. Specific features of the annealing (at temperatures as high as 800°C) of radiation defects are also reported. The electronic structure of nonrelaxed V_As, V_In, As_In, In_As defects is calculated. A relation between the electrical properties and the Fermi level position in irradiated InAs on the one hand and the electronic structure of the intrinsic defects and special features of the energy-band spectrum of InAs on the other hand is discussed.     

Electrical properties and structure of chalcogenide glasses containing bivalent tin

Two valence states of tin atoms are identified by Mössbauer and X-ray photoelectron spectroscopy in (As₂Se₃)_1?z (GeSe) _z?x (SnSe) _x glasses; it is shown that the presence of bivalent tin in the structural network of a glass does not give rise to impurity conductivity and impurity optical absorption. It is suggested to regard (As₂Se₃)_1?z (GeSe) _z?x (SnSe) _x and (As₂Se₃)_1?z (GeSe₂) _z?x (SnSe₂) _x glasses as semiconductor solid solutions whose electrical properties depend both on the electrical properties of the starting components and on the composition of the solid solutions.     

Photoelectric properties of surface-barrier structures based on Zn<Subscript>2−2<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>In<Subscript>x</Subscript>Se<Subscript>2</Subscript> films obtained by selenization

p-Zn_2?2xCu_xIn_xSe₂ (ZCIS) polycrystalline films 1–2 ¼m thick have been obtained by selenization. Photosensitive surface-barrier In/p-ZCIS structures are fabricated based on the films. The spectra of relative quantum efficiency of the structures obtained by selenization of the initial ZnSe/(Cu-In) and (Zn-Cu-In) films are examined. The optical band gap of the Zn_2?2xCu_xIn_xSe₂ films is determined. Conclusions are reached on the prospects for the use of the obtained films as broadband photoconverters of natural optical radiation.     

Chemical bonding and elastic constants of certain ternary III–V solid solutions

The chemical bonding of GaP, InP, InAs, InSb, and InBi binary compounds was investigated as well as the modification of the bonding in Ga_xIn_1?xP, InAs_xSb_1?x, and InSb_1?xBi_x semiconductor alloys; this modification occurs as a result of variation in the composition characterized by the parameter x. An approach based on the consideration of the total valence charge density, the chemical-bonding polarity, and the transverse effective charge was used. The elastic constants of the aforementioned ternary solid solutions were calculated, and the influence of chemical-bonding modification on these constants was analyzed. Local strains and composition disordering in the alloys under consideration drastically affect the dependences of the quantities under investigation on solid-solution composition. Thus, the above effects cannot be neglected in investigating substitutional solid solutions.     

Study of optical characteristics of structures with strongly strained In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As quantum wells

Results of photoluminescence (PL) studies of heterostructures with strongly strained InxGa_{1 ? x} As quantum wells (QWs) are presented. It is shown that the dependence of the PL intensity on the QW thickness has a maximum whose position depends on the composition of the In _x Ga_{1 ? x} As solid solution. The PL wavelength at the maximum intensity is 1.13 µm at a QW thickness of 60 µm at a QW thickness of 50 Å for x = 0.39 and 0.42, respectively.     

Thermodynamic stability and redistribution of charges in ternary AlGaN,InGaN, and InAlN alloys

A model of the delta lattice parameter is used to study the thermodynamics of AlGaN, InGaN, and InAlN alloys. The phase diagrams obtained indicate that AlxGa_1?xN is stable in the entire range of x, whereas the miscibility gap corresponds to 0.2 < x < 0.69 for InxGa_1?xN and to 0.16 < x < 0.7 for In_xAl_1?xN at 1000 K. Biaxial stresses lower the critical temperature and narrow the miscibility gap. The charge-density distribution is analyzed using the pseudopotential method to obtain an approximation of 32-atom supercells. The results of the analysis show that the stability of these alloys is controlled by the competition between the destabilizing contribution of strains related to the mismatch between the lattice constants and a stabilizing charge exchange between various chemical bonds. Biaxial stress reduces the charge redistribution caused by strains and thus increases the stability of an alloy.     

Electroluminescence in a semimetal channel at a single type II broken-gap heterointerface

The radiative recombination at the broken-gap p-GaInAsSb/p-InAs type-II interface is investigated in the temperature range of 4–100 K. It is shown that the electroluminescence band hν_A=0.37 eV can be attributed to a large extent to the recombination of electrons from the semimetal channel at the interface with the participation of a deep acceptor level at the interface. At the same time, the band hν_B=0.40 eV corresponds to radiative transitions in the InAs bulk to a shallow acceptor level. The participation of the interface states in the recombination across the GaInAsSb/InAs type-II interface becomes appreciable due to the overlapping of wave functions of holes, which are localized at the interface on the solid-solution side, with the wave functions of deep acceptor states.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

1 550 nm long-wavelength vertical-cavity surface emitting lasers

A 1 550 nm long-wavelength vertical cavity surface emitting laser (VCSEL) on InP substrate is designed and fabricated. The transfer matrix is used to compute reflectivity spectrum of the designed epitaxial layers. The epitaxial layers mainly consist of 40 pairs of n-AlxGayIn(1-x-y)As/InP, and 6 strain compensated AlxGayIn(1-x-y)As/InP quantum wells on n-InP substrate, respectively. The top distributed Bragg reflection (DBR) mirror system has been formed by fabricating 4.5 pairs of SiO2/Si. The designed cavity mode is around 1 536 nm. The dip of the fabricated cavity mode is around 1 530 nm. The threshold current is 30 mA and the maximum output power is around 270 μW under CW operation at room temperature.     

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.     

The boson peak in Raman spectra of As<Subscript>x</Subscript>S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> glasses

The Raman spectra of As_xS_1?x glasses with x < 40 at % (Z < 2.4) have been studied in a wide temperature range (20–300 K). A well resolved boson peak is observed in the low-frequency portion of the spectrum, not withstanding the appearance of floppy modes in the glasses under study. It is shown that the boson peak is characterized by two parameters: intensity and the peak position. A comparison of the intensity variation for the boson peaks indicates that the degree of disorder increases as x decreases. This effect is caused by floppy modes in the glass network and by sulfur phase separation. Studies of reduced boson peaks in the Raman spectra of As_xS_1?x glasses confirms the theoretical assumption that the shape of the peaks is independent of composition and temperature.