Optical technique for determining surface recombination velocity and bulk lifetime in silicon nanowire arrays

Silicon nanowire (SiNW) arrays have become a promising structure for photovoltaics in which the surface recombination velocity is an important parameter. In this study, a simple and cost-effective method is presented for producing large-area SiNW arrays with various lengths. We then employ an optical technique based on resonant-coupled photoconductive decay (RCPCD) to provide a contactless measurement for the determination of the surface velocity and bulk lifetime of SiNW arrays. The basic method is to probe the decay of total excess carrier concentration by varying the excitation wavelengths. However, as the initial carrier distribution could be very complicated in SiNWs, we have developed a rigorous couple wave analysis (RCWA) to calculate the absorption of SiNWs in order to obtain the initial distribution of excess carriers. The total excess carrier concentration as a function of time can then be derived by using the simulation results for experimental curve fitting. The model successfully fits the measured data and extracts parameters, which helps to determine both the bulk lifetime and the surface recombination velocity.