Computer analysis of photon-induced non-equilibrium phenomena at Si and AlGaAs surfaces

A theoretical analysis of the surface recombination, surface band bending and photoluminescence (PL) under strongly absorbed light illumination was performed for n-type Si and AlGaAs surfaces. A very strong dependence of the so-called effective surface recombination velocity (S_eff), surface photovoltage (SPV) and photoluminescence quantum efficiency (Y_PL) on both the excitation intensity and surface Fermi level position was found from rigorous computer calculations. The initial surface band bending was varied from accumulation to inversion by introducing the surface fixed charge (Q_FC) in the Si case, and from weak to strong depletion by increasing the surface state density (N_SS0), in the AlGaAs case. It was revealed that S_eff can be significantly reduced (almost four orders of magnitude on Si surface) by shifting the surface Fermi level towards band edges. On the other hand, a deep quenching of PL efficiency was observed for the values of N_SS around midgap above 5 × 10¹⁰ cm^-2 eV^-1 on AlGaAs surface. In addition, a comparison of simulated Y_PL dependencies versus photo-excitation with the experimental data obtained for MBE-grown AlGaAs layers passivated by ultrathin Si interface control layer was performed. This technique of passivation is known to reduce the interface state density down to the range of 10¹⁰ cm^-2 eV^-1.