Effect of indium doping on transient transport phenomena in semi-insulating GaAs

Abstract

The influence of defect structure on transient transport phenomena was investigated in semi-insulating GaAs, undoped and doped with In, grown by the liquid-encapsulated Czochralsky technique. The change in time after a strong laser excitation of the nonequilibrium photo-Hall effect voltage and the photomagnetoelectric effect were used to reveal the influence of In doping in concentrations of up to $>~2\ifmmode\times\else\texttimes\fi{}{10}^{20}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ We did not find additional In levels in the band gap. Nevertheless In doping caused significant changes in the behavior of nonequilibrium carrier mobility in the temperature range of 300--420 K, which were not observed in other crystals, undoped or doped with other dopants. The effect of In becomes pronounced if its concentration exceeds $(6--9)\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ These changes could not be explained only by the reduction of the dislocation density. We conclude that apart from this the rearrangement of the microscopic inhomogeneities must be taken into account. It is supposed that lattice defects become distributed more homogeneously, and appear more probably as small (short-range) inhomogeneities instead of large accumulations around dislocations. This leads to the diminished role of the percolation phenomena. It was demonstrated that though doping with In reduces the dislocation density, it can intensify the effect of smaller defects on transport phenomena.