Recombination induced non-equilibrium phase transitions in semiconductors

The thesis analyzes various carrier generation-recombination (g-r) models in semiconductors for possible non-equilibrium phase transitions. A general macroscopic theory is formulated for the steady states of non-equilibrium systems. The work then proceeds in three steps (i) stability analysis of the steady states of a g-r model and establishment of a possible phase transition behaviour, (ii) a study of the phase transition behaviour near the critical point and (iii) a stochastic analysis of the phase transition. Autocatalysis provided by electric field induced impact ionization and/or stimulated creation of bose particles such as excitons and non-linearities of the radiative and Auger recombination processes are essential ingradients of a g-r model exhibiting non-equilibrium phase transitions.Yost of the g-r models considered in this work displayed second-ordertype transitions, however first-order-type transitions are possible in coupled boson-fermion systems when higher order autocatalytic processes are taken into consideration. When diffusion and drift are taken into account fluctuations induce a spatial correlation function which is of the well known exponential form in simple cases and the correlation length diverges near the critical point. The' stochastic master equation leads to a nonPoissonian steady state distribution and the uniqueness of the distribution breaks down under the conditions of the realization of a phase transition behaviour. The effects of explicit inclusion of carrier generation-recombination on the Gunn instability are shown to be unimportant unless the diffusion constant vanishes, in which case the instability criterion is modified by putting a lower bound on the negative differential conductivity.</p