A New Method for the Electronic and Chemical Passivation of GaAs Surfaces using CS 2
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ABSTRACT A new GaAs surface passivation method, CS 2 treatment at moderate temperature was developed for effective passivation of GaAs surfaces. The CS 2 treatment of GaAs surfaces at 350 'C and 10 atm leads to deposition of a homogeneous film, with a thickness of several hundred A. The passivation layer thus produced causes a significant enhancement in room temperature photoluminescence intensity and the passivation effect of the sulfide film was confirmed by Raman spectroscopy. The passivation layer remained electrically and chemically stable over a period of nine months under ambient atmospheric conditions. In-depth Auger electron spectroscopy (AES) revealed that the carbon and oxygen content in the film was negligible, whereas sulfur was uniformly distributed throughout the film. A metal-insulator-semiconductor diode whose insulating layer is produced by the CS 2 treatment shows well-defined accumulation and depletion regions in its capacitance-voltage (C-V) characteristics with low hysteresis. INTRODUCTION Although GaAs has many physical properties that are superior to silicon as a semiconducting material, it has only limited application in the semiconductor device industry today, partly because of the inability to passivate the GaAs surface properly. The air-exposed GaAs surface is well known to have a high density of surface states, midgap pinning of Fermi level, and Schottky barrier heights that are nearly independent of metal work function. Several attempts have been made to circumvent this problem, and one of the most promising approaches is treatment of the GaAs surface with sulfur-containing solutions [1-3]. Despite the dramatic improvement in the GaAs surface characteristics after this type of treatment, a serious problem with these schemes is the short duration of the passivation effect obtained. Continuous photoluminescence (PL) measurements [4] have shown that the passivation effects obtained from prior sulfide treatments were completely lost only a few hours after the passivated surface was exposed to ambient air. This aging effect was also reported in the device characteristics of a (NH 4)2S-treated GaAs metal-insulator-semiconductor field-effect transistor (MISFET) [5]. The instability of the previous sulfide methods seems to originate from the susceptibility of the passivated GaAs surface to re-oxidation. There have been efforts to grow relatively thick sulfide films using the metal organic chemical vapor deposition (MOCVD) technique [6], and coating with As2S3 followed by annealing [7]. While these methods have demonstrated some improvements in surface properties, they are not completely satisfactory and there still seems to be a need to develop a more reliable passivation technique for GaAs. In 1994, LeRolland el al. [8] reported a technique for synthesis of rare-earth and transition metal sulfides from the oxides under high CS 2 pressure at 350-600 'C. This technique was used 529 Mat. Res. Soc. Symp. Proc. Vol. 406 © 1996 Materials Research Society
for easy preparation of bulk polysulfide c
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