COMPUTER-SIMULATION OF THE PHOTOLUMINESCENCE DECAY AT THE GAAS ELECTROLYTE JUNCTION .1. THE INFLUENCE OF THE EXCITATION INTENSITY AT THE FLAT-BAND CONDITION

The influence of excitation intensity, surface recombination velocity, and photocurrent on the time-resolved photoluminescence (PL) at the n -GaAs-electrolyte junction under flat band conditions was investigated using computer simulations. The mathematical background of the two-di mensional semiconductor analysis package (TOSCA) will be presented. We will show that the effects may be characterized qualitatively by expo nential fit function(s), although in most cases the simulated PL decay is nonexponential. For a free carrier concentration n(0) = 5 x 10(17) cm(-3), under the conditions of low injection density (p(i)) and with flat bands, both the surface recombination and the photocurrent lead to a remarkable decrease in the FL decay time either for surface recom bination velocities S-0 > 10(3) cm/s or for exchange photocurrent dens ities j(ph,0) > 10(-11) A/cm(2). Under the conditions chosen in this w ork, the PL decay time approximated by the monoexponential decay time T decreases to a minimum value in T-min = 1.64 ns when S-0 greater tha n or equal to 10(6) cm/s or j(ph,0) > 10(-8) A/cm(2). This minimum ind icates that the diffusion of the minority carriers toward the surface where they immediately nonradiatively vanish by means of surface recom bination and/or charge transfer, respectively, is limited by the therm al velocity. In both cases, diffusion competes effectively against bul k recombination. For injection levels (p(i)/n(0)) > 0.1, the PL decay time decreases with increasing injection density because the quadratic recombination process dominates. At high injection densities, the sur face recombination velocity may not remain constant during the PL deca y, but instead varies as a function of time S(t); S may decrease from its maximum value (S-0) by up to 1 order of magnitude during the PL de cay. The results will be discussed in relation to experimental results published previously by other groups.