Sulfur doping of GaAs with (NH4)(2)S-x solution

Abstract

A novel technique for sulfur doping to GaAs was demonstrated. The surface of GaAs was treated with (NH4)(2)S-x solution, subsequent to annealing using either furnace or rapid thermal processing. Sulfur atoms adsorbed at the surface of GaAs during the (NH4)(2)S-x treatment diffuse into GaAs during the annealing. The diffusion profiles of sulfur in both types of annealing treatments show a concave shape from the GaAs surface. Diffusion constants of sulfur determined using the Boltzmann-Matano technique increase with the decrease of sulfur concentration via the depth from the surface of GaAs. This suggests that immobile sulfur donor S-As(+) forms at the near surface interacts with a Ga divacancy, and results in the production of mobile As interstitials, I-As. The I-As moves fast toward the inside of GaAs and kickout the S-As(+) donor, producing a fast diffusing species of interstitial S atoms. The diffusion coefficients of sulfur determined are 2.5X10(-14) cm(2)/s at 840 degrees C and 5X10(-12) cm(2)/s at 900 degrees C. The sulfur doping technique is applied to the fabrication of metal-semiconductor field-effect transistors (MESFETs). The MESFETs with 1.0 mu m gate length exhibit transconductance of 190 mS/mm, demonstrating the applicability of this technique to the formation of active channel layer of MESFETs. (C) 1999 American Institute of Physics. [S0021-8979(99)09002-7].