Interpretation of laser absorption measurements on 4H-SiC bipolar diodes by numerical simulation

The interpretation and evaluation of free carrier absorption experiments on SiC devices is essentially supported by computer simulations of the measurement process, which exploits the physical effect that the light absorption coefficient in a semiconductor depends on the electron and hole concentrations. Hence, the attenuation of a laser beam transmitted through a sample is an integral function of the local charge carrier density along the optical path. We investigated time-resolved absorption profiles in 4H-SiC pin-diodes in the high-injection regime at current densities of 100 A/cm2. Based on ldquovirtual experimentsrdquo we studied the factors limiting the spatial resolution or disturbing the absorption signal such as Fabry-Perot interferences.