Non-contact evaluation of photodiode performance by laser beam induced current imaging

This work reports on the application of laser beam induced current (LBIC) to the determination of the product of zero-bias dynamic resistance and area, R₀A, of homojunction photodiodes. The technique involves using LBIC to measure temperature dependent values of the photocarrier spreading length of a particular device, and then fitting the theoretical temperature dependence. The photocarrier spreading length is a measure of the rate of decay of photoinduced forward bias of the p-n junction with distance from the location of electron-hole pair generation and is partly responsible for the shape of the LBIC profile. The LBIC magnitude is not required to be measured in any quantitative sense, although there is a requirement that the photocarrier spreading length be shorter than the device length in order for it to be measurable. The technique provides a non-contact method of determining the performance of individual devices within large two-dimensional focal plane arrays of photodiodes. Experimental results from Hg_0.77Cd_0.23Te infrared photodiodes are presented to demonstrate the procedure.