Measuring minority-carrier diffusion length using a Kelvin probe force microscope

A method based on Kelvin probe force microscopy for measuring minority-carr ier diffusion length in semiconductors is described. The method is based on measuring the surface photovoltage between the tip of an atomic farce micr oscope and the surface of an illuminated semiconductor junction. The photog enerated carriers diffuse to the junction and change the contact potential difference between the tip and the sample, as a function of the distance fr om the junction. The diffusion length L is then obtained by fitting the mea sured contact potential difference using the minority-carrier continuity eq uation. The method was applied to measurements of electron diffusion length in GaP pn and Schottky junctions. The measured diffusion length was found to be similar to 2 mu m, in good agreement with electron beam induced curre nt measurements.