TRANSIENT PHOTOLUMINESCENCE DECAY STUDY OF MINORITY-CARRIER LIFETIME IN GAAS HETEROFACE SOLAR-CELL STRUCTURES

Transient photoluminescence decay has been studied theoretically and experimentally as a technique for the investigation of GaAs solar cell materials and solar cell structures. The time-dependent continuity equation was solved using two variable boundary conditions modelling the interface between the emitter and hetero-window layer (AlGaAs) and between the emitter and space charge region, respectively. The solution was found with help of the Fourier transform method and the method of residues. There results an analytical expression for the time dependent photoluminescence (PL) intensity. The influence of various solar cell parameters on this photoluminescence transient has been studied in detail. An experimental investigation of transient PL decay was performed using a synchronously pumped mode locked and cavity dumped Nd:YAG/dye laser system for excitation and an optical sampling oscilloscope as the detector. GaAs wafers with and without surface passivation have been measured as well as hetero-window pn-structures and processed solar cells. A fit of the theoretical PL transients to the measured transients allows surface and bulk recombination parameters to be determined.