Investigation of deep-level states in bulk and low-temperature MBE semi-insulating GaAs by admittance transient spectroscopy

Deep-level states in low-temperature-grown MBE GaAs are analyzed from the viewpoint of thermal stability. Gallium vacancy Va-related states have two annealing stages with the on-set temperature at about 310 and 430 "C. Low temperature stage is connected with mobile arsenic interstitial As;, while an interaction between Va and arsenic antiside Asc. is dominant in the later stage. Essential annealing kinetic characteristics were determined for both stages. Finally, the migration enthalpy for Asc, and the formation enthalpy of annealing of the EL6 state were estimated. A. IntroductionGallium arsenide grown by molecular-beam epitaxy technique at low substrate temperatures (hereafter LTG GaAs) has became an important material because of its properties such as an extremely high excess of arsenic, a high resistivity and a very short charge carrier lifetime.These unusual parameters have attracted great attention of device technologm [l] as well as solid-state physicists. An extended literature on structural electrical and optical properties of LTG GaAs has been built over past years. Moreover, as the LTG GaAs contains an abundance of various defects, it is considered as an excellent object for the study of native defects of the GaAs lattice and interaction between them. In LTGGaAs arsenic antisite ha and V G~ seem to dominate [2]. These defects were already observed in very early studies [3,4] and are involved in one of the models of LTG GaAs material [SI. However, apart from of isolated &, and Vaa , information about other mainly complex defects is limited.In this contribution we present results of an analysis of annealing characteristics of deep-level states observed in the LTG GaAs. Information achieved as the order of the annealing kinetics and the enthalpy of annealing process allowed us to estimate a very probable microscopic configuration of several native defects present in the LTG GaAs. B. ExperimentalThe annealing kinetics analysis of deep-level states (hereafter DLS) was performed on LTG MBE GaAs layers grown at 250 "C. We chose the growth temperature as low as possible to obtain a large concentration of various defects inside the layers, but to avoid a deteriorating effect of hopping conduction on the measurement of deep-level states spectra. 2 pm thick LTG GaAs layers were grown on N' conductive GaAs substrates in a standard MBE system. The growth temperature was measured by a thermocouple attached to a substrate holder. The VDII ratio was maintained at 19. After growth samples were cleaved fiom the substrate and were subjected to the series of the isochronal and the isothermal annealing procedures. The analysed structures had the Au-Schottky contact onto the LTG GaAs layer and an ohmic contact &om the substrate side. The deep-level states spectra were studied by admittance transient spectros-0-7803-31 79-6/96 $5.00 0 1 996 IEEE 67

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“…The deep-level states spectra were studied by admittance transient spectros- conductor. Details about the ATS are presented elsewhere [6].…”

Section: B Experimentalmentioning

confidence: 99%