Influence of Point Defects on GaAs Devices
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INFLUENCE OF POINT DEFECTS ON GaAs DEVICES DAVID C. LOOK University Research Center, Wright State University, Dayton, OH
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ABSTRACT From electron-irriadiation sLudies, it is known that point defects can strongly affect the electrical properLies of GaAs-based MESFET's, MODFET's, solar cells, resonant-tunneling diodes, MIMIC circuits and other devices. As an example, 1 x 016 cm-2, 1 MeV electrons reduce the transconductance Fortunately, in a 1 pm by 200 pan MESFET by nearly an order of magnitude. annealing at 350 0 C for 10 min. can largely restore the device performance, although riot without some adverse effects. Point defects, or simple point defect complexes, can also exist in as-grown GaAs and affect devices in several different ways. For example, an As-rich stoichiometry can lead to an abundance of Ga vacancies, and thus to a higher Si donor activation in implanted MESFET devices; however, it can also promote an increase in As another example, unwanted impurities which sit on the Ga site. extremely high (> 3 x 1019 cm-3 ) concentrations of As arntisites, which are found in MBE GaAs grown at 2009C, lead to very unusual electrical and optical properties, and make possible a highly useful buffer material anid a very fast photoconductive switch. However, there are also adverse effects here, such as slow-transients in some MODFET devices, which may result from defect diffusion. Thus, the effects of point defects in GaAs devices must be understood. INTRODUCTION In any semiconductor material system, the influence of impurities on the electrical and optical properties is usually undlerstood well before that of defects. There are probably three major reasons for this situation: (1) beginming materials are typically full of impurities, which then dominate the electrical and optical properties; (2) impurities are needed for controlled doping, and thus are studied in great detail anyway; and (3) impurities are normally much easier to detect, identify, and quantify than defects. By and large, the GaAs material system has also For example, both followed this path, and is in the latter stages. liquid-encapsulated Czochralski (LEC) ard vertical gradient freeze (VGF) bulk semi-insulating (SI) ingots can now be grown with impurity contents in the low 1015 uM-3 [1]. Since several known electrically-active defects in GaAs often have concentrations this high or higher, their presence must be considered ira compensation models (2]. Defects can enter a semiconductor lattice through nmany different avenues, such as growth conditiors, irradiation, or stress. However, it is important to understand that the simplest defects, i.e., vacancies anid interstitials, probably exist as isolated species only after light-parLicle (electron) irradiation, because heavy-particle irradiation and stress tend to produce more massive damage (complexes, precipitates, and dislocations), and any high-temperature process (> 3000C), such as growth, will cause the (In fact, vacancies and interstitials to move around, and find sinks [2]. However, there in
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