R. M. Imamov

Electrical and structural properties of PHEMT heterostructures based on AlGaAs/InGaAs/AlGaAs and δ-doped on two sides

The pseudomorphic AlGaAs/InGaAs/AlGaAs heterostructure δ-doped with silicon on both sides and used for fabrication of high-power transistors is optimized to obtain a high concentration ns and mobility of two-dimensional electron gas in the quantum well (ns ≈ 3 × 1012 cm−2). Electrical and structural characteristics of the samples grown by molecular-beam epitaxy with various doping levels are studied. It is shown that the mobility and concentration of electrons varies as doping level is increased and the subbands of dimensional quantization are sequentially filled. In order to analyze the distribution of electrons in subbands of the heterostructure, the Shubnikov-de Haas oscillations at the liquid helium temperature were studied. The quality of the heterostructure layers was assessed using the method of X-ray diffraction. The data of photoluminescence spectroscopy are in good agreement with the results of calculations of the band structure.

Investigation of lattice distortions in InP crystals implanted with Fe+ ions by means of high‐resolution x‐ray diffraction and x‐ray standing‐wave methods

Lattice distortions due the implantation of Fe+ ions in InP semi‐insulating crystals have been investigated by means of high‐resolution x‐ray‐diffraction and x‐ray standing‐wave methods. The effects of both the implantation dose and the annealing time were studied. It is shown that the x‐ray standing‐wave method provides valuable complementary information on strain and damage in the subsurface layer and permits one to distinguish between different distortion profiles that give practically the same kinematical diffraction curve.

Determination of the Photoelectron Emission Probability with Inclined X-ray Laue Diffraction

A simple relation has been established between the Fourier component of the probability density P(z) of photoelectron emission from different depths of a crystal and the angular dependence of the emission of photoelectrons formed in inclined X-ray Laue diffraction, which for the first time permitted the use of a direct method for the reconstruction of the P(z) function. Accurate measurements of the angular dependence of photoelectron emission were carried out on a silicon single crystal with diffraction of Cu K,~ radiation for different energy ranges. Photoelectrons were recorded by a proportional gas counter specially designed for the energy analysis of photoelectrons under inclined Laue diffraction conditions. The laws predicted by the theory have been fully confirmed, and the corresponding P(z) functions have been obtained.

Study of new designs for the InAlAs metamorphic buffer on GaAs substrates with distributed compensation of elastic deformations

Two new designs for a metamorphic buffer, which are modifications of the InxAl1 − xAs metamorphic buffer due to groups of layers with differing lattice parameters, are proposed and implemented. This makes it possible to affect the relaxation of the metamorphic buffer. The structural and electrical characteristics of the obtained metamorphic HEMT nanoheterostructures are also studied.

Asymmetric X-Ray Diffraction

Abstract Physical phenomena characteristic of asymmetric X-ray diffraction schemes for perfect crystals, including diffraction under conditions of specular reflection, have been considered in detail. The principles underlying asymmetric crystal monochromators, achievements in obtaining narrow collimated X-ray beams, and the latest results on the application of asymmetric schemes in the investigation of thin subsurface layers are stated; along with the fundamentals of asymptotic Bragg diffraction, specific features of the grazing Bragg-Laue scheme and the analysis of amorphous sublayers with the use of the surface Bragg peak. Emphasis is placed on the application of asymmetric diffraction schemes in the method of X-ray standing waves to increase sensitivity (in recording of photoelectrons, fluorescence, and Compton scattering) and to study the characteristic features of the diffraction process in strongly asymmetric geometry.

Structural and electrical properties of quantum wells with nanoscale InAs inserts in InyAl1 − yAs/InxGa1 − xAs heterostructures on InP substrates

A complex study of the effect ofintroduction of nanoscale InAs inserts of different thicknesses into an In0.53Ga0.47As quantum well on the electrical properties and structural features of In0.50Al0.50As/In0.53Ga0.47As/In0.50Al0.50As nanoheterostructures with bilateral δ-Si doping grown on InP substrates has been performed. The layers of nanoheterostructures with a weak lattice mismatch are found to be equally (cube-on-cube) oriented. The introduction of a nanoscale InAs insert leads to an increase in mobility. At an insert thickness of about 1.8 nm, the effect of increasing mobility is saturated due to structural deterioration. The segregation of the second (apparently, wurtzite) phase is revealed; this process, as well as the formation of other defects in the nanoheterostructure layers, is due to local strains caused by variations of the indium content in the layers.

X-Ray diffractometry of metamorphic nanoheterostructures

Elastic strains in active regions of metamorphic transistor nanoheterostructures In0.7Al0.3As/In0.7Ga0.3As/In0.7Al0.3As on GaAs substrates with a metamorphic buffer (MB) having different complex designs have been determined by X-ray diffractometry. The objects of study are linear-graded MBs with different thicknesses, including those with internal strain-balanced superlattices or internal inverse steps, and a step-graded MB. All MBs are completed with an inverse step. The experimental results are compared with model predictions for hypothetical linear-graded MBs with the same average compositional gradients as for the samples under study.

Simultaneous analysis of double-crystal X-ray rocking curves from a set of crystallographic planes

A technique of simultaneous analysis of rocking curves from different crystallographic planes of multilayer semiconductor heterostructures is developed and implemented. By the example of the GaAs-InxGa1−xAs/GaAs(001) heterostructure with a quantum well and the rocking curves from the (004), (113), and (115) planes, it is demonstrated that simultaneous analysis makes it possible to derive both more reliable and more exhaustive information on the thickness, strain, and degree of amorphization of individual layers and interfaces in this heterostructure. The procedure developed can be used effectively to analyze arbitrary experimental data sets obtained by different X-ray methods sensitive to the general set of structural parameters.

Structural diagnostics of 'quantum' layers by X-ray diffraction and standing waves

We analyze the possibility for simultaneous adequate treatment of angular dependencies of the X-ray diffraction reflectivity and photoelectron yield (X-ray standing waves method) in order to extract the structural characteristics of semiconducting materials with ultra fine inclusions. Facilities of such an approach for evaluation of the degree of structural perfection of the layers, the phase shift of upper layers with respect to the buffer, the lattice parameters of particular layers and interfaces between them are demonstrated within the analysis of heterostructures based on the Si matrix with the Si1-xGex quantum wells and on the GaAs matrix with the InAs quantum dots.

Characterization of porous InP(001) layers by triple-crystal X-ray diffractometry

The structure of porous layers fabricated on the surface of an InP(001) semiconductor wafer by electrochemical oxidation has been studied by triple-crystal X-ray diffractometry. It is shown that, depending on the probe potential (current density), column-shaped pores of two types with different orientations with respect to the substrate are formed. It is established that, at a probe potential of ∼6 V, pores are extended along the current lines (CLO pores) and directed normally to the sample surface. With a decrease in the potential to ∼3 V, the longitudinal axes of pores are oriented at an angle of ζ = 52° ± 2° to the sample surface (CO pores). The average diameter and length of pores are determined (∼80 and 300–900 nm, respectively) and the porosity of the samples is evaluated (P ∼ 40–60%). The obtained data on the pore parameters are in satisfactory agreement with the scanning electron microscopy data.