G. B. Galiev

Effect of the built-in electric field on optical and electrical properties of AlGaAs/InGaAs/GaAs P-HEMT nanoheterostructures

This study is concerned with the photoluminescence spectra and electrical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high-electron-mobility transistor (P-HEMT) structures with a quantum well grown at different depths Lb with respect to the surface. The samples are produced so as to make the concentration of electrons in the quantum well unchanged, as the barrier layer thickness Lb is reduced. It is established that the photoluminescence spectra of all of the samples exhibit peaks at the photon energies ħω = 1.28−1.30 and 1.35–1.38 eV. The ratio between the intensities of these peaks increases as Lb is decreased. Calculations of the band structure show that variations in the spectra are due to the fact that the built-in electric field increases as the quantum well is set closer to the surface.

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.

Electron transport and optical properties of shallow GaAs/InGaAs/GaAs quantum wells with a thin central AlAs barrier

Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three-monolayer thick AlAs central barrier have been investigated for different well widths and Si doping levels. The transport parameters are determined by resistivity measurements in the temperature range 4–300 K and magnetotransport in magnetic fields up to 12 T. The (subband) carrier concentrations and mobilities are extracted from the Hall data and Shubnikov–de Haas oscillations. We find that the transport parameters are strongly affected by the insertion of the AlAs central barrier. Photoluminescence spectra, measured at 77 K, show an increase of the transition energies upon insertion of the barrier. The transport and optical data are analysed with the help of self-consistent calculations of the subband structure and envelope wavefunctions. Insertion of the AlAs central barrier changes the spatial distribution of the electron wavefunctions and leads to the formation of hybrid states, i.e., states which extend over the InGaAs and the delta-doped layer quantum wells.

Metamorphic nanoheterostructures for millimeter-wave electronics

Electrical parameters and root-mean-square surface roughness of the metamorphic InAlAs/InGaAs/InAlAs nanoheterostructures with different indium contents (0.30–0.55) have been investigated. Field-effect transistors with the gate length Lg = 140−265 nm fabricated on the basis of metamorphic nanoheterostructures with an indium content of ~40% in the channel exhibit the current and power gain cutoff frequency fC = 147 GHz and fmax = 266 GHz, respectively.

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.