TIME-RESOLVED PHOTOLUMINESCENCE AND MICROWAVE CONDUCTIVITY AT SEMICONDUCTOR ELECTRODES - DEPLETION LAYER EFFECTS

Analytical expressions which include depletion layer effects on low-in jection carrier relaxation are being presented for the first time here . Starting from the continuity equation for the minority carriers, we derive expressions for the output signal pertinent to time-resolved mi crowave and luminescence experiments. These are valid for the time dom ain that usually overlaps with the time scales of surface processes, s uch as charge transfer and trapping. Apart from the usual pulse form o f illumination, theoretical expressions pertaining to other forms of i llumination such as switch-on and switch-off transient modes, a period ic mode, and a steady state and their various inter-relationships are derived here. The expressions obtained are seen to be generalizations of existing flat-band low-injection results in the Limit of early or i nitial band bendings. The importance of the depletion layer as an expe rimental parameter is clearly seen in the limit of larger band bending s wherein it is shown, unlike the flat-band case, to exhibit pure expo nential forms of carrier relaxation. Our results are consistent with t he main conclusions of the numerical and experimental work published r ecently. Furthermore, this work provides the actual functional relatio nships between the applied potential and observed carrier decay. This should enable one to extract the surface kinetic parameters, after dec iding on the dominant mode of carrier relaxation at the interface, whe ther charge transfer or trapping, by studying the potential dependence of the fate of relaxation.