Ionizing-Radiation Response of the GaAs/(Al, Ga)As PHEMT: A Comparison of Gamma- and X-ray Results

An experiment is reported on the effect of ⁶⁰Co gamma rays or 45-keV x-ray photons on the GaAs/(Al, Ga)As PHEMT. It is shown that x-ray treatment can improve the dc performance of the device in some cases. This finding is attributed in part to the annealing or modification of DX centers.     

Investigation of the structural properties of GaAs layers grown by molecular-beam epitaxy at low temperatures

The results of an investigation of the structural perfection of GaAs epitaxial films grown by molecular-beam epitaxy at low growth temperatures (240–300 °C) and various As/Ga flux ratios (from 3 to 13) are presented. Diffraction reflection curves display characteristic features for the samples before and after annealing in the temperature range from 300 to 800 °C. Hypotheses which account for these features are advanced. The range of variation of the arsenic/gallium flux ratio, in which low-temperature growth takes place under nearly stoichiometric conditions, is established. Fiz. Tekh. Poluprovodn. 31, 1168–1170 (October 1997)     

n-AlGaAs/GaAs/n-AlGaAs double quantum wells with an AlAs barrier: Relating the cladding doping level to structural and transport properties

Double quantum wells in the form of an AlGaAs/GaAs/AlGaAs heterostructure with an AlAs barrier a few monolayers thick are fabricated by MBE. Their structural and compositional characterization is carried out by double-crystal XRD and SIMS. Electron mobility is evaluated by Hall-effect measurements for different quantum-well thicknesses. Conditions are identified under which electron mobility can be enhanced by introduction of an ultrathin barrier into a single quantum well. The findings are analyzed from the viewpoint of interface structural quality.Translated from Mikroelektronika, Vol. 34, No. 2, 2005, pp. 98–109.Original Russian Text Copyright © 2005 by Vasilevskii, Galiev, Ganin, Imamov, Klimov, Lomov, Mokerov, Saraikin, Chuev.     

Deep-level trapping centers in heterostructures for GaN field-effect transistors

Structural and electrophysical properties of heteroepitaxial gallium nitride layers on a sapphire substrate that are grown via the molecular beam epitaxy (MBE) method are studied. The parameters of deep-level trapping centers are determined by the method of the thermostimulated capacitor discharge; the degree of perfection of the film and substrate are determined by the two-crystal X-ray spectrometry method. The following structures are studied: i-GaN (1–2 μm)/GaN 〈Si〉(0.1−0.4 μm) and multilayer structures (Al_0.3Ga_0.7N-GaN-Al_0.3-Ga_0.7N-GaN-Al₂O₃) grown via the MBE method on a sapphire substrate. The effect of reactive ion etching on the energy spectrum of deep-level trapping centers in gallium nitride is studied. The obtained results are used to calculate the energy spectrum of defects in gallium nitride structures. Original Russian Text ? M.S. Andreev, L.E. Velikovskii, T.S. Kitichenko, T.G. Kolesnikova, A.P. Korovin, V.G. Mokerov, S.N. Yakunin, 2007, published in Radiotekhnika i Elektronika, 2007, Vol. 52, No. 7, pp. 880–887.     

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 n _s and mobility of two-dimensional electron gas in the quantum well (n _s ≈ 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.     

A Study of (In,Ga,Al)As/GaAs Quantum-Dot Heterostructures by X-ray Diffraction and Total Reflection

The structure of (In,Ga,Al)As/GaAs stacks with one to three layers of self-assembled InAs quantum dots is studied by high-resolution x-ray diffractometry and x-ray reflectometry. It is shown that the quantum dots are almost pyramidal in shape. It is found that (i) a first InAs layer, 2.7 ML thick, is invariably produced with a faceted surface and (ii) vertical coupling of quantum dots and superlattice formation do occur (with three quantum-dot layers). It is demonstrated that combining the two methods provides researchers with more reliable structural data.     

A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor

It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.     

Electrical behavior of modulation-and delta-doped Al x Ga1 − x As/In y Ga1 − y As/GaAs PHEMT structures

Modulation-and delta-doped Al_xGa_{1 ? x} As/In_yGa_{1 ? y} As/GaAs PHEMT structures are grown by MBE. The effect is examined of changes in the technique and level of doping on the electrical behavior of the structures. Photoluminescence spectroscopy combined with Hall-effect measurements is shown to be an effective strategy for the purpose. The experimental results are interpreted on the basis of calculated conductionband diagrams.     

The use of the amphoteric nature of impurity silicon atoms for obtaining planar p-n junctions on GaAs (111)A substrates by molecular beam epitaxy

Epilayers of the n-and p-type were grown. It is demonstrated that the surface relief of the p-type layers is inferior to that of n-type layers. However, in both cases, the photoluminescence spectra and charge carrier mobility have no considerable distinctions from these characteristics for single-crystal samples. Planar p-n junctions were obtained, and diodes were fabricated as well. Depending on the layer structure, the current-voltage characteristics for devices take a form typical of conventional or inverted diodes.     

Ultraquasi-hydrodynamic electron transport in submicrometer field effect MIS transistors and heterotransistors

It is shown that electrons in the channel of submicrometer field effect transistors have no time to be heated to quasi-steady-state temperatures corresponding to a balance between the Joule heating and thermal relaxation. This “underheating” contributes to an increase in the effective mobility of charge carriers as compared to the value of μ(E) corresponding to the drift-diffusion approximation. Using a reduction of the thermal-balance equation by eliminating the relaxation-related term, a simple analytical expression is obtained for current-voltage characteristics. In particular, the saturation current in the developed ultraquasi-hydrodynamic model is found to be proportional to (V _G -V _t ) ^3/2 . The results of measurements of characteristics of the test GaAlAs/InGaAs/GaAs P-HEMTs with the channel length of about 0.3 μm are reported; these results verify the adequacy of the developed model, the accuracy of which can only increase with a further decrease in the channel length. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 2, 2000, pp. 239–242. Original Russian Text Copyright ? 2000 by Gergel’, Mokerov, Timofeev, Fedorov.