Measuring Minority Carrier Diffusion Length Using High-Injection Scanning Photocurrent Microscopy

Scanning photocurrent microscopy (SPCM) has been widely used for characterizing charge transport properties, in particular, the minority carrier diffusion length of semiconductors. However, studying lightly doped or intrinsic semiconductors using SPCM remained challenging. Methods used in previous work required low levels of optical injection, which could not be fulfilled easily in semiconductors with lower carrier concentration. In this work, using finite-element simulation, we show that the minority diffusion length can also be quantified under high optical excitation. Not only being applicable both doped and intrinsic semiconductors, the method also lifted the restriction of implementing a Schottky contact in testing devices -- a condition assumed to be necessary in previous studies. The results significantly expanded the versatility of SPCM in studying a broad spectrum of semiconducting materials with unprecedented flexibility in experimental conditions.