Investigation of transient transport effects in semi-insulating GaAs caused by defect state change and their interaction

We investigated the transport of nonequilibrium charge carriers in semi-insulating liquid encapsulated Czochralski grown GaAs. The temporal changes of the Hall mobility were analysed after strong photo-excitation over long time intervals. They ranged up to 3000 cm2 V−1 s−1 and depended sensitively on the crystal technology, defect nature and concentration. The maximum mobilities were anti-correlated with the dislocation density, while for the stationary values no clear correlation was found. In all crystals a long-lasting saturation of the mobility took place, which in some cases was interrupted by a ‘step-like’ increase or decrease. Different scattering centres appeared to be effective at different time intervals. The changes in the product of their concentration and scattering cross section were up to 2 × 106 cm−1. The observed effects confirm the influence of complex scatterers. It could have been defect associations and dislocations with Cottrell spheres, which created drift and recombination barriers of different heights. Screening by carriers changes not only the effective barrier heights, but the effective volume of the inhomogeneities and the drift paths of the carriers as well. The associations of scattering centres especially can be divided into smaller centres.