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The nature of the external quantum efficiency’s drop in the AlInGaN-based light-emitting diode’s heterostructures at high pumping has been considered. The temperature dependence of the external quantum efficiency has been investigated for two types of heterostructures with an active region located in the n- and p-type regions. It is found experimentally that the temperature dependence of the external quantum efficiency at high pumping for these two types of heterostructures is different. It is shown by numerical simulation that this difference is due to the unlikely behavior of the carrier injection’s efficiency into the active region of heterostructures with n- and p-type active regions. The results obtained indicate a key role of the injection mechanism in the drop of the external quantum efficiency at high pumping. [ABSTRACT FROM AUTHOR]

Heterostructures with single strained InGaAs/GaAs quantum wells have been studied by measuring the capacitance-voltage characteristics in a wide range of temperatures and test signal frequencies. Based on the analysis of experimental capacitance-voltage characteristics, a temperature shift of the peak in the apparent profile of a majority carrier’s concentration is revealed and a quantitative model of this phenomenon is proposed. The effect of incomplete impurity ionization on the experimentally found quantum well’s charge is determined. It is established by numerical simulation and fitting of capacitance-voltage characteristics that the conduction band’s discontinuity for heterostructures with strained In xGa1 − xAs/GaAs quantum wells ( x = 0.225) remains constant and equal to 172 ± 10 meV at temperatures from 320 to 100 K. [ABSTRACT FROM AUTHOR]

The control effect of the ferroelectric polarization on the two-dimensional electron gas (2DEG) in a ferroelectric/AlGaN/GaN metal–ferroelectric–semiconductor (MFS) structure is theoretically analyzed by a self-consistent approach. With incorporating the hysteresis nature of the ferroelectric into calculation, the nature of the control effect is disclosed, where the 2DEG density is depleted/restored after poling/depoling operation on the MFS structure. The orientation of the ferroelectric polarization is clarified to be parallel to that of the AlGaN barrier, which, based on an electrostatics analysis, is attributed to the pinning effect of the underlying polarization. Reducing the thickness of the AlGaN barrier from 25 nm to 20 nm leads to an improved control modulation of the 2DEG density from 36.7% to 54.1%. [ABSTRACT FROM AUTHOR]

Simulation of multicomponent AlInGaN-based heterostructures for their use in light-emitting diodes is performed. The effect of nonuniform distribution of In atoms in the light-emitting “nanodiodes” on the working characteristics of the device in general are determined. A model describing the structure of multicomponent AlInGaN heterostructures for light-emitting diodes is developed. [ABSTRACT FROM AUTHOR]

It is experimentally found that the maximum drift velocity of electrons in quantum wells of differently arranged AlGaAs/GaAs heterostructures and pseudoamorphous Al0.36Ga0.64As/In0.15Ga0.85 As heterostructures is higher than the maximum drift velocity of electrons in bulk materials. It is established that no negative differential conductivity is exhibited by the field dependence of the drift velocity of two-dimensional electrons in GaAs and In0.15Ga0.85As. The drift velocity in the GaAs quantum well is saturated in fields several times higher than the field corresponding to the Γ- L intervalley transitions of electrons in bulk GaAs. [ABSTRACT FROM AUTHOR]

We describe experiments investigating the quality of ohmic contacts to both bulk GaN and to III-nitride heterostructures. Titanium-based contacts were investigated to assess the role of intermixing and surface impurities for contact formation to n-type GaN. Direct contact to the two-dimensional electron gas in GaN/AlGaN heterostructures was also studied. These contacts were made by photochemical etching of the samples to expose the heterointerface. It was observed that even in the latter case contact annealing leads to a lower contact resistance by consuming surface contaminants and promoting beneficial interfacial reactions. Various passivation techniques were tried to reduce surface leakage current between contact pads and PECVD-deposited silicon nitride was found to be the best material for this application. [ABSTRACT FROM AUTHOR]

The photoresponse time of the cyclotron resonance detector to terahertz radiation under integer quantum Hall effect conditions in the GaAs/AlGaAs heterostructure is shown to have a deep minimum at the Hall plateau center and two sharp maxima at the plateau edges. The minimum at the plateau center is associated with the fundamental property of vanishing of the random impurity potential screening under quantum Hall effect conditions. The decrease in the response time outside the plateau is related to the equilibrium population of the Landau level above (under) the Fermi level by electrons (holes), respectively, which increases the probability of photoexcited carrier recombination. It is shown that, under conditions of background radiation (300 K), relaxation times decrease by two orders of magnitude while retaining the characteristic magnetic field dependence. [ABSTRACT FROM AUTHOR]

For field-effect transistors based on heterostructures with selective doping, the results of calculations for the output characteristics of devices on the basis of the hydrodynamic model are compared with those based on the quasi-hydrodynamic (temperature-related) model. It is shown that the transverse spatial transport and heavy dependences of relaxation times on energy lead to the situation where the results of calculations based on the above models differ appreciably from one another at the gate lengths that much exceed the length of electron relaxation by momentum. [ABSTRACT FROM AUTHOR]

Layers of the GaSb1 − 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. [ABSTRACT FROM AUTHOR]

We have studied the electrical characteristics of photodiodes based on p-GaSb/ p-GaInAsSb/ N-GaAlAsSb heterojunctions and investigated the mechanisms of current transfer in these heterostructures at various temperatures. A comparison of the theoretical results and experimental data showed that the tunneling charge transfer mechanism dominates at low temperatures ( T < 150 K) under both forward and reverse bias conditions. The tunneling current becomes a determining factor at an electric field strength in the p- n junction of no less that 105 V/cm, which is related to a small bandgap width of the materials studied and low effective masses of electrons and holes. [ABSTRACT FROM AUTHOR]

The formation of axial heterostructures in filamentary nanocrystals (nanowhiskers) is considered within the framework of a two-component diffusion growth model. An expression for the thickness of a heteroboundary is obtained, which is consistent with the available experimental data. Under the usual growth conditions, the thickness of the zone of diffusion smearing of the heteroboundary is on the order of one atomic monolayer, which ensures the high quality of heteroboundaries in nanowhiskers. [ABSTRACT FROM AUTHOR]

Studies of the properties of InGaAsN compounds and methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures grown by molecular beam epitaxy on GaAs substrates are reviewed. The results for different types of heterostructures with quantum-size InGaAsN layers are presented. Among those are (1) traditional InGaAsN quantum wells in a GaAs matrix, (2) InAs quantum dots embedded in an (In)GaAsN layer, and (3) strain-compensated superlattices InAs/GaAsN/InGaAsN with quantum wells and quantum dots. The methods used in the study allow controllable variations in the emission wavelength over the telecommunication range from 1.3 to 1.76 μm at room temperature. [ABSTRACT FROM AUTHOR]

It is shown that capture of the surface (interface) phonons can occur in a double-barrier heterostructure in addition to the capture of bulk polar optical phonons. The strength of interaction of electrons with confined interface phonons becomes lower as the thickness of the phonon well (a semiconductor layer where phonons are captured) is decreased. A new approach is suggested for reducing the scattering of electrons by polar optical phonons in a double-barrier quantum well; this approach is based on separate capture of phonons in narrow phonon wells. The calculated scattering rate with the capture of interface phonons into the GaAs/InAs/GaAs and AlAs/GaAs/AlAs quantum wells taken into account is found to be much lower than the rate obtained in the approximation of scattering of electrons by bulk phonons. A multifold decrease in the rate of electron-phonon scattering in the AlAs/GaAs/AlAs quantum well is obtained by separating this well by the monomolecular InAs layer that is transparent for electrons but acts as a reflecting barrier for polar optical phonons. [ABSTRACT FROM AUTHOR]

The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications. [ABSTRACT FROM AUTHOR]

The Fourier spectra of oscillations of magnetoresistance in the heavily doped Al x Ga1 − x As:Si/GaAs heterostructure, with filling of the two size-quantization subbands, the ground subband E m and the excited subband E p , are studied. In the concept of the probabilities of intrasubband and intersubband transitions involving the Landau levels, the origin of harmonics at the frequencies F m ± F p in the oscillations of magnetoresistance are interpreted. The ratio between the peak amplitudes A m and A p at the frequencies F m and F p of the harmonics is close to unity, with equal probabilities of the relations A m / A p > 1 and A m / A p < 1. At A m / A p > 1, the damping of the Landau quantization is controlled by the Coulomb potential, whereas at A m / A p < 1 it is controlled by relaxation of two-dimensional electrons due to the heterointerfacial roughness. [ABSTRACT FROM AUTHOR]

Simulation methods based on the energy-balance equation are used to study the electrical conductivity of layered nanosized heterostructures in high electric fields. A quasi-hydrodynamic description of the electron drift is used with regard to the diffusion and thermal-diffusion components of the current, the divergence of the electron heat flux, and the temperature dependence of the electron mobility and energy relaxation time. Current-voltage characteristics are obtained for a layered heterostructure with a barrier height of 0.3 eV and with lengths of both the narrow-and wide-gap layers equal to 50 nm. Depending on the doping level in the range (5–1) × 1017 cm−3, the characteristics exhibit either a sharp peak of the differential conductivity or a bistability loop corresponding to the thermal-injection instability. A physical model is suggested that attributes the shape of the calculated current-voltage characteristics to the cumulative effect of the electrostatic lowering of the heterobarrier height and the increase in electron temperature near the injecting heteroboundaries. [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]

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 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]

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]

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: 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]