A set of transfer and output current-voltage characteristics of a bipolar transistor with a short-period superlattice in the emitter region has been calculated. It is shown that the presence of a superlattice in the tr ansistor structure leads to the fo rmation of a negative differential conductivity region, which makes it possible to implement not only amplification, but also the generation and multiplication of high-frequency oscillations.

In this work a bilayer moiré graphene structure with a spatial period of energy parameters change of the ten nanometers order is considered. The layer misorientation angle effect and the energy gap parameter on the current-voltage characteristic of the structure is studied numerically. The transmission coefficients calculation through the structure demonstrates the appearance of energy gaps, the magnitude of which depends on the misorientation angle of the layers.

Computational and experimental studies of the characteristics of a high-power AlGaAs/InGaAs/GaAs DpHEMT were performed. A self-consistent numerical solution of the Schrodinger and Poisson equations was used to calculate the band diagram and the electron concentration in the channel of the transistor under study. The electron mobility in the transistor channel was estimated experimentally at 9300 cm2/V·s. The obtained transfer current--voltage characteristic of the transistor was used to calculate the parameters of a model differential amplifier (small-signal gain and third-order non-linear distortion factor). Keywords: AlGaAs/InGaAs/GaAs DpHEMT, nonlinear distortion, spacer layers.

The paper presents the results of studies of C–V characteristics of GaAs/In0.53Ga0.47As HEMT before and after neutron irradiation with a fluence of (6.3 ± 1.3) × 1014 cm–2. Based on the experimentally obtained characteristics, the effective electron distribution profiles of the structure were calculated before and after radiation impact. The effect of radiation defects on the δ-layers of the structure was analyzed.

In this work a bilayer moiré graphene structure with a spatial period of energy parameters change of the ten nanometers order is considered. The layer misorientation angle effect and the energy gap parameter on the current-voltage characteristic of the structure is studied numerically. The transmission coefficients calculation through the structure demonstrates the appearance of energy gaps, the magnitude of which depends on the misorientation angle of the layers.

An experimental and theoretical study is performed of the change in the slope of current–voltage characteristics in the area of negative differential conductivity. Reasons are considered for the stepwise rise in current at high voltages inside superlattices with few (6–18) periods. Also examined is the effect of transitional layers of the superlattice that are used to enhance the injection of electrons into the active region at the junction of the metal contact and the n + layer–superlattice contact.

In this paper, we propose a method for predicting the refractive index variation in InGaAlAs tunnel-coupled quantum wells under the action of an electric field. Complex of mathematical and experimental studies to optimize the heterosystems design forthe semiconductor modulator construction according to a planar Mach-Zehnder interferometer scheme is demonstrated.

In this paper, we propose a method for predicting the refractive index variation in InGaAlAs tunnel-coupled quantum wells under the action of an electric field. Complex of mathematical and experimental studies to optimize the heterosystems design forthe semiconductor modulator construction according to a planar Mach--Zehnder interferometer scheme is demonstrated. Keywords: Mach--Zehnder modulator, nanoheterostructure, quantum mechanical calculations, refractive index, transmission electron microscopy, photoelectric spectroscopy.

The paper presents the results of modeling the electrophysical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures via self-consistent solution of the Schrödinger and Poisson equations. On the basis of numerical calculations, a method for analyzing nonlinear distortions of the transfer current–voltage characteristics of such transistors is proposed. The effect of the spacer layers and the doping level of the δ layer on the nonlinearity of the current–voltage characteristics is estimated.

The electrophysical parameters and surface morphology of n / n – GaAs structures with Schottky contacts before and after exposure to neutrons with an average energy of ~1 MeV are studied. Changes in the electron concentration and mobility profiles in the structures are determined by capacitance–voltage measurements. Using atomic force microscopy, radiation-induced defect clusters are revealed; a comprehensive approach to determining their parameters is proposed.

The electrophysical parameters and surface morphology of GaAs n/n- structures with Schottky contacts before and after neuron impact with an average energy of about 1 MeV were studied. Changes in the profiles of the concentration and mobility of electrons in the structures were determined by the C-V method measurements. The method of atomic force microscopy helped to find radiation defect clusters which appearing during impact. A complex approach to the determination of their parameters is proposed.

The nonlinearity of the gate–drain current–voltage characteristics in classical Schottky transistors and two-dimensional electron gas field-effect transistors based on AlGaAs/InGaAs/GaAs and InGaAs/GaAs compounds is analyzed. The carrier velocity-overshoot effect in the transistor channel is analyzed for various doping profiles of the structures under study.

The size-quantized energy subbands and envelope wave functions for [001] quantum wells based on zinc-blende III–V semiconductors are numerically calculated using the eight-band Kane model and finite-difference discretization scheme in coordinate space. The effect of the quantum-well band parameters and external electric field oriented along the structure growth direction on the ratio between the Rashba and Dresselhaus spin–orbit coupling parameters is studied. It is demonstrated that at certain electric-field values the spin–orbit coupling parameters in GaAs/InGaAs structures can be equal, which ensures the condition for forming stable spin helices. In addition, it is established that the spin–orbit coupling linear in wave vector in symmetric GaAs/InGaAs wells can disappear under certain well widths and barrier chemical compositions.

We present a study of electron gas properties in InAs nanowires determined by interaction between nanowire geometry, doping and surface states. The electron gas density and space distribution are calculated via self-consistent solution of coupled Schroedinger and Poisson equations in the nanowires with a hexagonal cross-section. We show that the density of surface states and the nanowire width define the spatial distribution of the electrons. Three configurations can be distinguished, namely the electrons are localized in the center of the wire, or they are arranged in a uniform tubular distribution, or finally in a tubular distribution with additional electron accumulation at the corners of the nanowire. The latter one is dominating for most experimentally obtained nanowires. N-type doping partly suppresses electron accumulation at the nanowire corners. The electron density calculated for both, various nanowire widths and different positions of the Fermi level at the nanowire surface, is compared with the experimental data for intrinsic InAs nanowires. Suitable agreement is obtained by assuming a Fermi level pinning at 60 to 100 meV above the conduction band edge, leading to a tubular electron distribution with accumulation along the corners of the nanowire.

InGaAs/GaAs heterostructures containing quantum wells and δ-doped layers are studied theoretically and experimentally. On the basis of the procedure of self-consistently solving the Schrödinger equation and Poisson equation, the differential capacitance and the apparent electron concentration profiles are numerically calculated for structures with different mutual arrangements of the quantum well and the δ layer. The results of the calculations are compared with the result of analyzing the experimental capacitance-voltage characteristics of the structures. The systematic features of the behavior of the apparent concentration profiles and capacitance-voltage characteristics in relation to the geometric properties of the structure, the temperature, and the doping level are established.

A comprehensive analysis of double tunnel-coupled InGaAs/GaAs quantum well heterostructures is carried out. The real composition profiles of the structures are obtained by high-resolution transmission electron microscopy and energy-dispersive spectrometry. The resultant profiles are compared with the profile obtained by computer simulation. By solving the Schrödinger equation in combination with the Poisson equation, the energy states for quantum-confined heterostructures with initially specified and real composition profiles are calculated. The influence of a number of factors, such as the well width, barrier thickness, and the background doping level on the properties of the heterostructure is thoroughly analyzed. In this manner, the optical characteristics and their dependence on the growth technology and geometric parameters of the structures are studied. Such an approach makes it possible to refine the real geometric parameters of wells and barriers and to correct the parameters of the structure and growth technology in order to improve the optical characteristics.

The photosensitivity, photoluminescence, and electroluminescence spectra of InGaAs/GaAs diode nanoheterostructures with a Si δ layer formed at a distance of 10 nm from the InGaAs quantum well are studied. The influence of the arrangement of the δ layer with respect to the quantum well on the optoelectronic properties of the structures is established.

An integrated approach to the analysis of tunnel-coupled InGaAs/GaAs quantum well heterostructures is suggested. In the approach, both experimental and theoretical investigation methods are used. Transmission electron microscopy combined with energy-dispersive X-ray spectrometry is used to determine the spatial distribution of the InGaAs alloy’s composition. The photoluminescence and photoconductivity spectra of the structures are recorded experimentally. In order to interpret the results in more detail, computer simulation of the epitaxial growth is performed. By simultaneously solving the Schrödinger equation and the Poisson equation, the energy states are calculated for the quantum-confined hetertostructure with initial and real composition profiles. The results of calculations are correlated with the data obtained for interband optical transitions from the analysis of the photoluminescence and photoconductivity spectra. Good agreement between the experimental and theoretical results is gained. The approach suggested in the study provides a means for refining the real geometrical features of the structure, for correlating the spectral results with the real composition profile of the structure, and for correcting the structural and growth parameters to improve the optical characteristics of the structure.

We demonstrate the feasibility to obtain electroluminescence (EL), up to room temperature, from InGaAs self-assembled quantum dots (QDs) included in a forward-biased Schottky diode. Moreover, using a ferromagnet (FM) as the contact layer, sizable circular polarization of the EL emission in the presence of an external magnetic field is obtained. A resonant behavior of the degree of circular polarization (P) as a function of the applied voltage (V), for a given value of magnetic field, is observed. We explain our findings using a model including tunneling of (spin-polarised) holes through the metal-semiconductor interface, transport in the near-surface region of the heterostructure and out-of-equilibrium statistics of the injected carriers occupying the available states in the QD heterostructure. In particular, the resonant P(V) dependence is related to the splitting of the quasi-Fermi level for two spin orientations in the FM. Copyright (C) EPLA, 2012

Comparative admittance measurements in mesadiodes on an n +-GaAs substrate and in ring planar diode structures on an i-GaAs substrate, which contain a Si δ-doped layer and an InGaAs quantum well in the GaAs epitaxial layer are performed. The possibility of determining the concentration profile and electron mobility in the vicinity of the δ-doped layer and the InGaAs quantum well is shown based on an analysis of the simultaneously measured capacitance-voltage and conductance-voltage characteristics of the mesadiodes. By performing such measurements for i-GaAs-based ring diode structures with the given geometry, it is possible to reliably determine only the concentration profile. The influence of the relative location of the quantum well and δ-doped layer on the concentration profile and mobility is revealed. The phenomenon of Maxwell relaxation in i-GaAs-based ring diode structures is discussed.