Effects of stoichiometry on thermal stability of undoped, semi-insulating GaAs

Abstract

We provide independent evidence of the effects of melt composition on the semi-insulating behavior and thermal stability of undoped GaAs crystals pulled from pyrolytic boron nitride crucibles by the liquid-encapsulated Czochralski technique. Semi-insulating crystals pulled from stoichiometric or As-rich melts show excellent stability to heat treatments, in contrast to semi- insulating Ga-rich material which exhibits p-type conversion after prolonged annealing at 860 °C. Deep level transient spectroscopy and Hall-effect measurements suggest that p-conversion is caused by outdiffusion of native As and/or Ga defects associated with the EL2 deep donors, resulting in uncompensated residual acceptors, predominantly carbon impurities at the surface. The measured mobility of undoped, semi-insulating GaAs is found empirically to be a sensitive parameter for qualifying substrates for direct ion implantation.