Instantaneous temperature profiles inside semiconductor power devices: Part II

In Part I, handling and interpretation of infrared thermal radiation signals have been treated for optically thick devices. If thin slices are to be analyzed, as is the case if high spatial resolution is required, interpretation becomes more difficult because the emissivity of silicon may deviate significantly from the asymptotic value for an optically thick slice. A method will be presented by which both temperature and emissivity can be determined point by point and with a time resolution of several microseconds purely from thermal radiation data. The solution relies on a radiating reference source which for convenience has been chosen as a surface emitting nearly black radiation at two distinct temperatures. The analysis of an operating thyristor shows that rather large temperature gradients across the thickness of the device may exist with the peak temperature being displaced asymmetrically toward the cathode