Measurement of Minority-Carrier Diffusion Coefficient in Silicon by AC Photo-Current Method

Abstract
The ac photo-current method was studied and improved theoretically as a method of determining the diffusion coefficient and lifetime mapping of a semiconductor wafer. It was found that if the diffusion length of excess carriers is greater than the junction depth of a p-n diode structure, the phase shift of the ac photo-current due to short-wavelength light is independent of the lifetime and is determined by the diffusion coefficient. If the diffusion length is shorter than the junction depth, on the other hand, the phase shift is influenced by the lifetime as well as by the diffusion coefficient. The results were used to measure the diffusion coefficient of holes in n-Si.