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The amplitude-frequency modulation of oscillations of the magnetoresistance of 2D electrons in an AlSb(δ-Te)/InAs/AsSb(δ-Te) quantum well is studied. In the dependence of the amplitude of the oscillations δ(1/ B) T = const, regions of negative Dingle temperature are observed. The anomalies in the dependence δ(1/ B) T = const are attributed to the fact that the quantizing magnetic field resonantly induces intersubband electron-electron interaction between the 2D electrons of the ground size-quantization subband and excited subband. The resonance fields B and the times corresponding to the collision-related broadening of the Landau levels are estimated. The concentration threshold of filling of the excited size-quantization subband is established at a level of n s ≈ 8 × 1011 cm−2. [ABSTRACT FROM AUTHOR]

Band diagrams and current-voltage and capacitance-voltage characteristics of isotype N +-GaSb/n0-GaInAsSb/ N +-GaAlAsSb heterostructures have been studied. Dark-current flow mechanisms have been analyzed. It is shown that a staggered type-II heterojunction can behave as a Schottky diode and its current-voltage characteristics exhibit rectifying properties over the entire temperature range 90–300 K. The thermionic-emission current predominates at high temperatures and low voltages. This current is due to thermal excitation of electrons from GaInAsSb to GaSb over the barrier at the heterointerface. A comparison of the relevant theoretical and experimental data confirmed that the tunneling charge transport mechanism plays the key role at low temperatures under both forward and reverse biases. [ABSTRACT FROM AUTHOR]

Conditions for the transition from the staggered heterojunction to the type-II broken-gap one were considered for isolated Ga1− x InxAsySb1− y /InAs(GaSb) heterostructures in relation to the quaternary alloy composition. Energy-band diagrams of such heterojunctions were estimated and energy band offsets Δ at the heterointerface were determined. It was experimentally found that the type-II broken-gap heterojunction in the Ga1− x InxAsySb1− y / p-InAs structure is observed in the entire range of composition parameters under study, 0.03 < x < 0.23, and becomes staggered in the range 0.3 < x < 1. In p-Ga1− x InxAsySb1− y / p-GaSb heterostructures with the indium content 0.85 < x < 0.92 in the solid phase, the p-type conductivity is observed, which is indicative of the staggered heterojunction. At x > 0.92, the contribution of electrons of the semimetal channel at the heterointerface to the total conductivity was observed, as well as the transition from the staggered heterojunction to the type-II broken-gap one. [ABSTRACT FROM AUTHOR]

Transport properties of a 2D electron gas located at a short distance from the surface (15–32.5 nm) in an AlGaAs/GaAs heterojunction were studied. A pronounced effect of the surface on the behavior of the conductivity of the 2D electron gas, as well as metallic gate screening of the scattering of two dimensional electrons by charged centers, were observed. [ABSTRACT FROM AUTHOR]

The possibility of controlling the effective lifetime of nonequilibrium carriers by varying the lattice mismatch between the interfaced materials of a heterostructure has been studied on the example of InGaAs/GaAs heterostructures. It was found that, at a given composition (thickness) of a lightly doped layer of the InGaAs alloy, the nonequilibrium carrier lifetime depends on its thickness (composition), which enables variation of the nonequilibrium carrier lifetime from several nanoseconds to a microsecond without any significant change in the concentration of mobile carriers. The results obtained were used to fabricate pulse p +- p 0-π- n 0- n + diodes with blocking voltages of up to 500 V, which can switch currents of ≥10 A and have recovery times no longer than 10 ns. [ABSTRACT FROM AUTHOR]

The spectra of electroluminescence, photoluminescence, and photocurrent for the In0.2Ga0.8N/GaN quantum-well structures are studied to clarify the causes for the reduction in quantum efficiency with increasing forward current. It is established that the quantum efficiency decreases as the emitting photon energy approaches the mobility edge in the In0.2Ga0.8N layer. The mobility edge determined from the photocurrent spectra is E me = 2.89 eV. At the photon energies hv > 2.69 eV, the charge carriers can tunnel to nonradiative recombination centers with a certain probability, and therefore, the quantum efficiency decreases. The tunnel injection into deep localized states provides the maximum electroluminescence efficiency. This effect is responsible for the origin of the characteristic maximum in the quantum efficiency of the emitting diodes at current densities much lower than the operating densities. Occupation of the deep localized states in the density-of-states “tails” in InGaN plays a crucial role in the formation of the emission line as well. It is shown that the increase in the quantum efficiency and the “red” shift of the photoluminescence spectra with the voltage correlate with the changes in the photocurrent and occur due to suppression of the separation of photogenerated carriers in the field of the space charge region and to their thermalization to deep local states. [ABSTRACT FROM AUTHOR]

The electron distribution over the quantum confinement subbands ( E m is the ground-state subband and E p is the excited subband) in the quantum well of a heavily doped heterojunction is discussed. The functional relation between the concentrations n m and n p in the E m and E p subbands, as well as the threshold value n c , agrees with the theory only qualitatively. This fact can be due to the existence of the density-of-states tails and to the quasi-two-dimensionality of the electrons in the E p subband. The measured nonzero concentration n p in the subthreshold region n m < n c is explained by the effect of pushing the n p electrons to the heterojunction plane by the internal electric field. [ABSTRACT FROM AUTHOR]

The transport characteristics and quantum oscillations of magnetoresistance have been studied in n-(001)GaAs/Al x Ga1− x As heterostructures at liquid helium temperatures and uniaxial compressions up to 3.5 kbar. Under such loading conditions, the density of two-dimensional (2D) electrons at the heterointerface is determined primarily by a piezoelectric field induced in the [001] direction. The screening of this field leads to an increase in the 2D electron density at the heterointerface under compression along the [110] axis and to a decrease in this density, under compression along the $$[1\bar 10]$$ axis. The formation and subsequent redistribution of a compensating charge at the heterointerface are impeded, which leads to the development of relaxation processes in the stressed system at sufficiently high pressures. The pressure dependences of the anisotropic mobility and the effective cyclotron mass of 2D electrons show that their energy spectrum remains isotropic and the dispersion obeys a parabolic law in the pressure range studied. [ABSTRACT FROM AUTHOR]

A stationary physical model of the p-i-n photodiode based on a two-dimensional drift-diffusion scheme of charge transport in multilayer InxGa1- x AsyP1- y /InP heterostructures is developed. The model takes into account the Fermi statistics for electrons and holes, charge carrier mobility dependence on the electric field and impurity concentration, as well as thermionic emission and tunneling at the heterointerfaces. The effect of design parameters on the characteristics of large area p-i-n photodiodes is analyzed and methods for increasing their dynamic range are suggested. [ABSTRACT FROM AUTHOR]

A method that enables direct observation and quantitative characterization of carrier leakage from the active region of working semiconductor light-emitting diodes and lasers is developed on the basis of Kelvinprobe microscopy. The method is used to reveal, on the surface of the mirror surfaces of high-power InGaAs/AlGaAs/GaAs laser diodes, minority holes arriving from the active region and spreading to the surface regions over the n-type emitter and n-type substrate. It is shown that holes can move through surface channels formed by regions of surface band bending to distances of tens of micrometers from the place where they originally appear at the surface. It is demonstrated that, as the injection current increases, the amount of leakage gradually grows and stabilizes after the onset of lasing. [ABSTRACT FROM AUTHOR]

It is shown that the self-sustained oscillations observed in weakly coupled GaAs/AlGaAs superlattices result from the superposition of sinusoidal oscillations of several coupled oscillators. Each oscillator is a single-barrier resonant tunneling diode. The coupled oscillators form an expanded boundary of an electric-field domain under conditions of negative differential conductance. [ABSTRACT FROM AUTHOR]

The study is devoted to theoretical explanation of a decrease in the electroluminescence efficiency as the pump current increases, which is characteristic of light-emitting-diode (LED) heterostructures based on AlInGaN. Numerical simulation shows that the increase in the external quantum efficiency at low current densities J ≈ 1 A/cm2 is caused by the competition between radiative and nonradiative recombination. The decrease in the quantum efficiency at current densities J > 1 A/cm2 is caused by a decrease in the efficiency of hole injection into the active region. It is shown that the depth of the acceptor energy level in the AlGaN emitter, as well as low electron and hole mobilities in the p-type region, plays an important role in this effect. A modified LED heterostructure is suggested in which the efficiency decrease with the pump current should not occur. [ABSTRACT FROM AUTHOR]

The 18-band kp model is used to analyze the wave functions of the states in the valence band. It is found that the typically used approximation based on the assumption that the effective masses are energy-independent for the band of light and heavy holes is justified only near the valence-band top. The conditions for matching of the envelope functions for holes at the GaAs/AlAs heterointerfaces with the (111) and (110) orientations taking into account and disregarding the spin-orbit interaction for energies in the vicinity of the valence-band top are considered. These conditions are derived as a result of simplifying the description of electronic states using the pseudopotential method. The matching conditions obtained are completely consistent with the problem’s symmetry. These conditions involve mixing of the envelope functions with their normal derivatives and mixing of derivatives with the functions. It is shown that the light and heavy holes are not mixed at the (111) heterointerface but are mixed at the (110) heterointerface. It is found that the states are mixed at resonance energies to a much greater extent at the (110) heterointerface than at the (001) interface. [ABSTRACT FROM AUTHOR]

In this paper, we report on the design and optical properties of laser diodes with an emission wave-length of ∼1170 nm based on an (InGa)As/GaAs double quantum well active layer. The back and front facet of the laser diodes were coated with SiOx dielectric films that influence the output optical power by enhancing or lowering the facet reflectivity. The measurements show improvement of the facet-coated laser diode properties in the threshold-current-density reduction along with light output power enhancement. Furthermore, a narrow far field pattern and high side mode suppression have been observed. [ABSTRACT FROM AUTHOR]

Electroluminescent structures that emit in the visible region of the spectrum and are based on porous silicon ( por-Si) formed on the p-Si substrate electrolytically using an internal current source are fabricated. The photoluminescent and electroluminescent properties, as well as the current-and capacitance-voltage characteristics of the structures are studied. Electroluminescence is observed only if the forward bias voltage is applied to the structure; the electroluminescence mechanism is based on the injection and is related to the radiative recombination of electrons and holes in quantum-dimensional Si nanocrystals. The injection of holes is controlled by the condition of their accumulation in the space-charge region of p-Si and by a comparatively low concentration of electronic states at the por-Si/ p-Si interface. The charge transport in por-Si is caused by the direct tunneling of charge carriers between the quantum-mechanical levels, which is ensured by an appreciable number of quantum-dimensional Si nanocrystals. The leakage currents are low as a result of a small variance in the sizes of Si nanocrystals and the absence of comparatively large nanocrystals. [ABSTRACT FROM AUTHOR]

Abstract: Based on detailed studies of the energy band structure and the optical transitions in very long wavelength (>14μm) GaAs/AlGaAs quantum-well (QW) infrared photodetectors (QWIPs), we have built a practical QWIP model. We study the factors that determine photogenerated carriers and response wavelengths of photocurrents of very long wavelength QWIPs. The material structures of QWIPs are first characterized by the photoluminescence measurements (PL) at room temperature and 77K respectively. We have found and confirmed a distinctive difference between photocurrent of QWIPs with only one confined state in the quantum well (QW) and those binding two confined states, which resulted in different dependence of detection wavelength on the quantum well width. Also, we have investigated the dependence of response wavelength on several other parameters for very long wavelength QWIPs, such as barrier width and Al mole fraction. By calculating the density of photogenerated carriers in the continuum above the energy barriers using the PL calibrated QWIP structures, we have demonstrated that due to the high sample quality, the photocarriers can be either in miniband states (Bloch states in the multiple quantum wells), or they transport from one quantum well to the next in the form of propagating waves. We have further calculated the densities of photocarriers in the QWIPs reported in the literature. It is shown that the Bloch wave boundary conditions are appropriate for QWIPs with narrow QWs, whereas propagating wave boundary conditions are appropriate for wide QWs. [Copyright &y& Elsevier]

Abstract: We study a vertically coupled three-layer single quantum dot under a magnetic field by the exact diagonalization of the Hamiltonian matrix. Effects of the inter-layer separation and the external magnetic field are reported. We find that dot–dot distance and electron–electron interaction strongly affect the low-lying states of the coupled quantum dots. The inter-dot correlation leads to the disappearance of some ground state transitions which are otherwise present in uncoupled dots. [Copyright &y& Elsevier]

Abstract: In this study, we have calculated the subband energy level, potential profile, and the corresponding wavefunction and chemical potential for different temperatures and donor concentrations in a spherical quantum dot self-consistently. We have also investigated the effect of exchange-correlation potential on the energy levels. In addition, we have checked the applicability of quantum genetic algorithm to a realistic self-consistent quantum dot problem. In all computations, the penetration of wavefunction to the barrier region is taken into account. [Copyright &y& Elsevier]

Abstract: This study examines the post-annealing-dependent behaviors of the shallow junction produced by implanting 1015 cm−2 20keV BGe ions into n-type 〈100〉 silicon specimens. Post-annealing treatments consisted of one- and two-step annealing including both furnace annealing (FA) and rapid thermal annealing (RTA). Comparison of the one-step FA at 550°C and the one-step RTA at 1050°C revealed that boron depth profiles were slightly diffused in the former but exhibited considerable transient-enhanced diffusion (TED) in the latter. However, both the one-step FA- and RTA-annealed germanium depth profiles barely diffused, while the latter diffusing slightly deeper than the former. The optimum value of junction depth (x j) times sheet resistance (R s) was obtained with one-step FA at 550°C for 1h. The two-step annealing (FA at 550°C and RTA at 1050°C) results showed that the RTA-induced TED in the boron depth profiles could be effectively retarded only when FA took place for more than 3h. Again, germanium depth profiles are also barely diffused while the corresponding TEDs were larger than those in one-step FA but smaller than those in one-step RTA. Furthermore, the two-step annealing of FA at 550°C for 3h followed by RTA at 1050°C for 30s is suggested when attempting to obtain an optimum value of x j R s. [Copyright &y& Elsevier]

Abstract: High electron mobility transistor (HEMT) structures consisting of: GaAs (buffer layer)/i-AlGaAs(spacer layer)/n-AlGaAs(barrier layer)/n-GaAs(cap layer) were grown by MBE on GaAs substrates. The optical properties of the HEMT structures were studied by photoreflectance (PR) spectroscopy at different temperatures. We observed in the PR spectra transitions located approximately at 1.41 and 1.85eV, associated with the energy band edges of GaAs and AlGaAs, respectively. Oscillatory signals slightly above these energies were recognized as Franz–Keldysh oscillations (FKO). By employing lasers with different wavelengths as modulation sources, and by varying the thickness of the layers in the heterostructures we were able to identify the origin of the PR signals in the spectra. The FKO close to the GaAs band gap originate at the GaAs buffer/i-AlGaAs heterojunction where the two-dimensional electron gas is localized. Finally, low-temperature PR experiments indicate that the oscillatory signal observed above the AlGaAs band edge is formed by two overlapped signals, one of which originates in the GaAs(cap)/n-AlGaAs interface. [Copyright &y& Elsevier]

Abstract: In this work, we study the molecular beam epitaxial growth of strained InGaAs alloys on InP in order to increase as far as possible the In content of the active layer of heterostructures. We show that a reduction of the growth temperature with respect to the 500°C usual one could be efficient to increase the critical thickness for strain relaxation but does not result in an electron mobility improvement. At 500°C, the maximum In content compatible with an active layer thickness of 10–15nm is 0.75. Within this framework, the electron mobility rises to 16 000 and 139 000cm2/Vs at 300 and 77K, respectively, for a heterostructure with a 140Å thick channel layer and a 400Å thick spacer layer. Both values are among the best ones ever reported for a InGaAs/InAlAs heterostructure. [Copyright &y& Elsevier]

Abstract: In this paper, we report on the properties of AlGaN/GaN/AlGaN HEMT structures grown by molecular beam epitaxy on resistive Si(111) substrates. The properties of the AlGaN buffer layer and the AlGaN/GaN HEMTs are presented. Finally, the static performances of long gate length devices demonstrate their interest for power applications. [Copyright &y& Elsevier]

Abstract: In this work, AlGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy (MBE) on silicon (111), silicon carbide and GaN templates on sapphire. The structural and electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active layer quality. Furthermore, an intercalated AlN layer grown on a GaN template is shown to enhance the insulating properties of the buffer. [Copyright &y& Elsevier]

Abstract: Lateral InAs quantum dot (QD) molecules are created by self-organized anisotropic strain engineering of a (In,Ga)As/GaAs superlattice (SL) template on GaAs (311)B by molecular beam epitaxy. During stacking the SL template self-organizes into a two-dimensionally ordered strain-modulated network on a mesoscopic length scale. InAs QDs preferentially grow on the nodes of the network due to local strain recognition. The QDs form a lattice of separated groups of closely spaced ordered QDs, whose number is controlled by the upper GaAs separation layer thickness on the SL template and the SL growth temperature. The QD molecules exhibit strong photoluminescence emission up to room temperature. [Copyright &y& Elsevier]

Abstract: A low-resistance ohmic contact to Mg-doped p-type GaN grown by metal-organic chemical vapor deposition (MOCVD) with a carrier concentration of 2×1017 cm−3 using Pd/Ni/Au metallization was formed. An anneal at 500°C for 1min in a flowing N2 ambient produced an excellent ohmic contact with a specific contact resistivity as low as 2.4×10−5 Ωcm2. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiles of Pd/Ni/Au contacts annealed at 500°C demonstrated a strong correlation between Ni and Pd interdiffusion toward the GaN surface and a reduction in specific contact resistance. The low contact resistance is attributed to the reduction of the native oxide by Ni diffusion along with the formation of Pd and Ni related-gallide phases at the p-GaN surface region. [Copyright &y& Elsevier]

Abstract: A theoretical study of multi-quantum-well semiconductor heterostructures under applied electric fields perpendicular to the layers is performed within the transfer-matrix approach. Calculations are carried out for two different variably spaced superlattices, designed in such a way that the conduction-electron states resonate at a certain value of the electric field. We have calculated the density of states for various values of the applied electric field, and results indicate a richly peaked structure associated to quasi-bound states of electrons, heavy holes and light holes. Results shown for the electric-field dependence of the interband transitions associated to electron–hole recombination indicate the possibility of a coherent resonant tunnelling, at a critical field, which may have applications in the design of more efficient solar-cell devices. [Copyright &y& Elsevier]

Abstract: The InP/GaAsSb/InP double heterostructure bipolar transistors with 20-nm-thick base layer are passivated by low-temperature deposited SiN x . The SiN x passivation results in an increase of the current gain, seen from common-emitter I–V characteristics. An improvement of the Early voltage is also observed after the passivation. The study of the forward Gummel plots shows that the collector current keeps unchanged, while the base current decreases after SiN x passivation. A decrease of the base current ideality factor is found by the SiN x passivation. The passivation also results in an improvement of the base–collector junction. In contrast, the leakage current of the base–collector junction increases tow orders after passivation. [Copyright &y& Elsevier]

Abstract: We calculate the diffusion thermopower for a degenerate two-dimensional electron gas in real lattice-mismatched semiconductor quantum wells (QWs) at low temperatures. We consider explicitly two scattering mechanisms: (i) the surface roughness-induced piezoelectric effect, a new important scattering source, arising due to a large fluctuating density of roughness-induced piezoelectric charges and (ii) the surface roughness. The scattering parameter of energy dependence of the momentum relaxation time and the diffusion thermopower , of each of the mechanisms separately and also when both the mechanisms are combined, are calculated as a function of electron concentration and well width. The diffusion thermopower, as a function of electron concentration, due to piezoelectric field shows a change in sign for lower concentrations. Interestingly, the diffusion thermopower, due to this mechanism, as a function of well width also shows a change in sign and it is dominant for larger well widths. The numerical calculations are presented for and AlN/GaN QWs. The piezoelectric mechanism is expected to be very important in systems with large piezoelectric constant and lattice mismatch. [Copyright &y& Elsevier]

We have performed a Monte Carlo simulation of the electron motion in a Landau-quantized GaAs/AlAs superlattice to investigate the effect of increasing the temperature on the miniband conduction. A strong drift-velocity enhancement is found to occur when cyclical phonon emission and absorption are taken into account. [Copyright &y& Elsevier]

Conducting polyaniline (PANI) was prepared by chemical oxidation polymerization in the presence of excess hydrochloric acid. Zinc sulfide (ZnS) thin films were deposited on glass substrates at the pressure of 10 mbar by thermal resistor evaporation technique. The solution of conducting PANI has been printed on pellet of ZnS using spin-coating technique. I- V characteristics of ZnS thin film and printed conducting PANI have been recorded at room temperature. The results indicated that I- V of conducting PANI shows non-ohmic behavior and I- V characteristic of conducting PANI printed ZnS, a PANI-ZnS heterojunction, shows the rectification effect and confirms that a diode can be fabricated by using simple technique. [ABSTRACT FROM AUTHOR]

Switching of properties of gallium arsenide heterostructure diodes has been studied. It is shown that use of a graded-gap base region or a wide-gap “wall” (abrupt heterojunction) enables control over the distribution of injected carriers and their accumulation near the p-n junction, which leads to a faster reverse-voltage recovery (60–70 ps). Structures are considered in which an impurity gradient is used, together with the gradient of the energy gap, in order to make the working voltage higher. [ABSTRACT FROM AUTHOR]

The effect of magnetic field on the current-voltage characteristic of the n-GaAs- p-Ge heterojunction is studied at 77 and 300 K. A slight variation in the forward and reverse currents of the heterojunction in a magnetic field is observed. It is established that the observed variation in currents of the heterojunction is mainly caused by variation in the potential barrier as a result of a change in the concentration of minority charge carriers as induced by a magnetic field. It is found that the voltage magnetosensitivity of the heterojunction is lower by an order of magnitude than the voltage magnetosensitivity of a germanium magnetodiode. [ABSTRACT FROM AUTHOR]

The effect of a quantizing static electric field parallel to the axis of a semiconductor superstructure on the charge-carrier mobility in the direction perpendicular to this axis is studied. The transverse conductivity of charge carriers was calculated on the basis of a quantum-mechanical kinetic equation. Using the results of the numerical analysis, the dependences of the time of the carriers’ momentum relaxation on their transverse energy and also the dependences of the charge-carrier mobility on the strength of the longitudinal quantizing electric field were plotted. It is shown that the dependence of the density of current flowing perpendicularly to the superlattice axis on the strength of the longitudinal electric field is oscillatory. [ABSTRACT FROM AUTHOR]

Abstract: The current density and the ideality factor of the non-radiative band-to-impurity recombination current in a p–n diode is calculated analytically in a very good approximation. The usual approximation of multiplying the maximum recombination rate with the width of the depletion layer is very crude. The ideality factor is found to be ⩽2, depending on bias and diffusion voltage. [Copyright &y& Elsevier]

Abstract: We report the results of spatially resolved micro-photoluminescence on self-organized InAs/GaAs quantum dots. Our results suggest that carrier thermal redistribution is linked to the effects of carrier migration in these quantum dots. The higher migration length was observed at 150K, making the higher carrier redistribution between the energy levels. [Copyright &y& Elsevier]