E. A. Klimov

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.

The effect of spacer-layer growth temperature on mobility in a two-dimensional electron gas in PHEMT structures

The effect of growth temperature of the AlGaAs spacer layer on mobility in a two-dimensional electron gas μe in single-side δ-doped pseudomorphic AlGaAs/InGaAs/GaAs transistor structures with a high electron mobility is studied experimentally. The energy-band diagram is analyzed using a self-consistent calculation. In order to study the electronic transport properties, an optimized structure in which there is no parallel conduction over the doped layer was chosen. It is shown that, in optimized structures, the mobility μe increases by 53% at T = 300 K and by 69% at T = 77 K as the growth temperature increases from 590 to 610°C, with the other parameters and the growth conditions remaining the same. It is assumed that this behavior is related to an improvement in the structural quality of the AlGaAs spacer layer and the AlGaAs/InGaAs/GaAs heteroboundary.

Investigation of the optical properties of GaAs with δ-Si doping grown by molecular-beam epitaxy at low temperatures

Molecular-beam epitaxy is used for the preparation of structures based on “low-temperature” grown GaAs with introduced d-Si doping. Specific features in the photon-energy range of 1.28–1.48 eV are observed in the photoluminescence spectrum after structures annealing at temperatures of 520 and 580°C; these features are related to the formation of point defects and their complexes. The “pump–probe” light transmission measurements reveal that the characteristic lifetimes of nonequilibrium carriers in the fabricated structures amount to Tc ≈ 1.2–1.5 ps.

Electron effective masses in an InGaAs quantum well with InAs and GaAs inserts

We have measured and calculated effective masses m* and the band structure of the In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well on the InP substrate with one or two InAs inserts in the quantum well and GaAs inserts in heterointerface barriers. The effective mass m* was measured by the Shubnikov?de Haas effect. Double symmetric InAs inserts in a quantum well lead to decreasing of m* by about 10%?35% as compared with the uniform In0.53Ga0.47As lattice-matched quantum well.

Electron mobility and effective mass in composite InGaAs quantum wells with InAs and GaAs nanoinserts

The paper is concerned with the theoretical and experimental studies of the band structure and electrical properties of InAlAs/InGaAs/InAlAs/InP heterostructures containing a composite InGaAs quantum well with InAs and GaAs nanoinserts. From the Shubnikov-de Haas effect, the effective cyclotron mass mc* is determined experimentally and calculated with consideration for the nonparabolicity of the electron energy spectrum. An approach to estimation of the effective mass is proposed and tested. The approach is based on weighted averaging of the mc* of the composite quantum well’s constituent materials. A first proposed heterostructure containing two InAs inserts symmetrically arranged in the quantum well makes a 26% reduction in mc* compared to mc* in the lattice-matched In0.53Ga0.47As quantum well possible.

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.

Electrical and optical properties of near-surface AlGaAs/InGaAs/AlGaAs quantum wells with different quantum-well depths

A series of AlGaAs/InGaAs/AlGaAs quantum-well heterostructures with different quantum-well depths and approximately the same concentrations of two-dimensional electrons is grown by molecular-beam epitaxy. The built-in electric field in the grown samples is determined from the photoreflectance data and, on this basis, the energy-band structure in the quantum-well region is calculated. It is found that the highest mobility μe of two-dimensional electrons is attained in the sample with a barrier-layer thickness of Lb = 11 nm. Measurements of the photoluminescence spectra and the band-structure calculations demonstrate that, as the quantum well becomes closer to the surface, the doping profile broadens due to diffusion and segregation processes. The nonmonotonic dependence of μe on the distance between the surface and the quantum well is explained.

Interrelation of the construction of the metamorphic InAlAs/InGaAs nanoheterostructures with the InAs content in the active layer of 76–100% with their surface morphology and electrical properties

The influence of the construction of a metamorphic buffer on the surface morphology and electrical properties of InAlAs/InGaAs/InAlAs nanoheterostructures with InAs content in the active layer from 76 to 100% with the use of the GaAs and InP substrates is studied. It is shown that such parameters as the electron mobility and the concentration, as well as the root-mean-square surface roughness, substantially depend on the construction of the metamorphic buffer. It is established experimentally that these parameters largely depend on the maximal local gradient of the lattice constant of the metamorphic buffer in the growth direction of the layers rather than on its average value. It is shown that, with selection of the construction of the metamorphic buffer, it is possible to form nanostructured surfaces with a large-periodic profile.

Structural and photoluminescence properties of low-temperature GaAs grown on GaAs(100) and GaAs(111)A substrates

Undoped, uniformly Si-doped, and δ-Si-doped GaAs layers grown by molecular-beam epitaxy on (100)- and (111)A-oriented GaAs substrates at a temperature of 230°C are studied. The As4 pressure is varied. The surface roughness of the sample is established by atomic-force microscopy; the crystal quality, by X-ray diffraction measurements; and the energy levels of different defects, by photoluminescence spectroscopy at a temperature of 79 K. It is shown that the crystal structure is more imperfect in the case of GaAs(111)A substrates. The effect of the As4 flux during growth on the structure of low-temperature GaAs grown on different types of substrates is shown as well.

Experimental determination of the electron effective masses and mobilities in each dimensionally-quantized subband in an InxGa1 − xAs quantum well with InAs inserts

HEMT structures with In0.53Ga0.47As quantum well are synthesized using molecular-beam epitaxy on InP substrates. The structures are double-side Si δ-doped so that two dimensionally-quantized subbands are occupied. The effect of the central InAs nanoinsert in the quantum well on the electron effective masses m* and mobilities in each subband is studied. For experimental determination of m*, the quantum μq and transport μt mobilities of the two-dimensional electron gas in each dimensionally-quantized subband, the Shubnikov-de Haas effect is measured at two temperatures of 4.2 and 8.4 K. The electron effective masses are determined by the temperature dependence of the oscillation amplitudes, separating the oscillations of each dimensionally-quantized subband. The Fourier spectra of oscillations are used to determine the electron mobilities μq and μt in each dimensionally-quantized subband. It is shown that m* decreases as the InAs-nanoinsert thickness d in the In0.53Ga0.47As quantum well and electron mobilities increase. The maximum electron mobility is observed at the insert thickness d = 3.4 nm.