Nonthermal Equilibrium Fluctuations of Electrons and Holes

A discussion is presented on the behavior of electron and hole fluctuations under steady-state conditions. The differences between steady-state and thermal-equilibrium systems, associated with microscopic reversibility, are briefly discussed. It is concluded that so far all calculations pertained to conditions valid for (quasi-) thermal equilibrium. To illustrate the features for a nonequilibrium state, an academic model involving cyclic transitions through one set of electron traps is analyzed. The variance is shown to be super-Poissonian in the range where the photoconductance is superlinear and sub-Poissonian in the range where all traps are filled. The connection with presently accepted two-center models for phosphors and photoconductors is also indicated.