NONLINEAR TRANSPORT AND STRUCTURE FORMATION IN SEMIINSULATING GAAS

We present an experimental study of slow domains in semi-insulating Ga As using time-resolved, two-dimensional electro-optic voltage probing. A detailed analysis of the shape of the bulk domains proves that they are formed by symmetric charge dipoles made up from ionized traps. Th e study of the dependence of the domain parameters on the applied volt age allows us for the first time to reconstruct experimentally the bul k j(E)-characteristic of SI-GaAs and to show that prevailing theoretic al models fail to explain the observations. The experimentally determi ned field dependence of the free-carrier concentration reveals a stron gly field-enhanced trapping with no critical field. The drift velocity of domains is experimentally found to be exclusively determined by th e free-carrier concentration at the centre of the domain.