Determination of minority-carrier diffusion length in a p-silicon wafer by photocurrent generation method

A nondestructive method to determine the diffusion length of minority carriers in a p-silicon wafer is outlined. This novel method is based on creating an accumulation layer on one side and an inversion layer on the other side of the wafer by depositing thin semitransparent layers of high (e.g., palladium) and low (e.g., aluminum) workfunction metals, respectively. The wafer acquires a structure akin to p+-p-n+ and is capable of generating a photocurrent when illuminated. The photocurrent Isc (where sc represents short circuit) as a function of the intensity Pin of a monochromatic radiation incident on the accumulation layer (p+) side of the wafer is measured. The diffusion length L is determined from the slope of the Jsc vs Pin curve. The values of L so determined were compared with that determined from the measurement of spectral response by illuminating the wafer from the inversion layer (n+) side and were found to be in excellent agreement.