An optical system for bilateral recombination-radiation diagnostics of the carrier redistribution in switching power devices

An optical scanning system is developed for the detection of recombination radiation from power devices. The instrument facilitates two-dimensional characterization of the excess-carrier content in a device. A bilateral technique enables measurements along various perpendicular surfaces of the devices under investigation. Hence, measurements of processes not present, or less dominant, in one direction may be observed in another. Examples taken from gate turn-off (GTO)-thyristor investigations are presented. All stages of the switching cycles as well as during the ON-state can be investigated with the instrument. Detailed three-dimensional carrier maps are produced for the visualization of measurement results, and sequences of maps are used to observe time-dependent phenomena involved in the transient operation of a device. Features associated with placement of the optical focus are explained, and possibilities of tomographic mapping of power devices are discussed