Annealing Characteristics Of Low Temperature Grown GaAs:Be
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ANNEALING CHARACTERISTICS OF LOW TEMPERATURE GROWN GaAs:Be 4 3 1 12 D.E. BLISS, , W. WALUKIEWICZ, K.T. CHAN, J.W. AGER III,1 S. TANIGAWA, and E.E. HALLER1,2
1. Center for Advanced Materials, Materials Science Division, Lawrence Berkeley Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720 2. Dept. of Materials Science, University of California at Berkeley, Berkeley, CA 94720 3. Hewlett-Packard Co. Microwave Technology Division, Santa Rosa, CA 95403 4. Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305, Japan ABSTRACT We have studied the annealing characteristics of acceptor doped GaAs:Be grown at Low substrate Temperatures (300'C) by Molecular Beam Epitaxy (LTMBE). The Be was introduced in 3 a range of concentrations from 1016 -1019 cm- . As-grown material was found to be n-type even 3 up to the highest Be concentration of 1019 cm- although Raman spectroscopy of the Be local vibrational mode indicates that the majority of the Be impurities are substitutional. We propose that Be acceptors are rendered inactive by the high concentration of AsGa-related native donor defects present. Results of slow positron annihilation studies indicate an excess concentration of VGa in LTMBE layers over bulk grown crystals. A distinct annealing stage at 500'C, similar to irradiation damaged and plastically deformed GaAs, marks a rapid decrease in the AsGa defect concentration. A second annealing stage at 800'C corresponds to the activation of Be acceptors. Analysis of isothermal annealing kinetics for the removal of AsGa-related defects gives an activation energy of 1.7 ±0.3 eV. We model the defect removal mechanism with the VGa assisted diffusion of ASGa to As precipitates. INTRODUCTION More than a decade ago it was proposed [1] that GaAs grown at low temperatures, -400*C, would make an excellent buffer layer for field effect transistors. Recently it was found that lowering the buffer layer growth temperature even further, -200-300'C, resulted in substantial performance improvements for GaAs integrated circuits [2]. It is this novel material grown at 200-300'C that we shall refer to as LTMBE GaAs which has generated great technological and scientific interest. Of great scientific interest is the extremely high quantity of excess As, -1.5% [3]. The excess As is incorporated mainly as AsGa-related defects [4] in as-grown material and as arsenic precipitates after annealing [5]. The extremely high concentrations of native defects in as-grown material provide a unique opportunity to study the reactions between native defects and/or intentionally introduced impurities in highly non-stoichiometric material. The high resistivity -104 to 105 f2cm, of LTMBE GaAs has been attributed to the high concentration of excess As. As grown, however, these materials exhibit conductivity characteristics of a hopping mechanism via defects [6]. Only after annealing the layers at temperatures above 500'C, such as encountered during the subsequent growth of a standard MBE layer, does the material become Semi-Insulating (SI) with resistiv
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