Wafer characterization via sub-nanosecond time-correlated single photon counting

The free charge carrier lifetime is a highly sensitive parameter that can be used for analyzing the function of semiconductor devices and monitoring the quality of wafer materials. In this context, time-resolved photoluminescence (TRPL) is presented as a technique for directly determining the free charge carrier lifetime with pulsed diode laser excitation and time-correlated single photon counting, employing highly sensitive single-photon avalanche detectors (SPADs). The full range in time-scales of charge carrier dynamics can be addressed with the capability to resolve luminescence lifetimes from approximately 50 ps up to several hundred microseconds. This is achieved with an instrument response function (IRF) as short as 100 ps and the capability of adjustable repetition rates in the pulsed laser excitation that can be adapted to the luminescence lifetime of the material. The technique is capable of correlating spectral information concerning material specific band gap transitions and transmission edges with the respective luminescence lifetimes in a specific spectral channel. This is particularly valuable for the analysis of multi-component systems. Furthermore, the general instrumentation can be combined with a raster scanning based microscope setup, which can be configured to cover lateral resolutions down to sub-μm scale and scan ranges from 100 microns up to several centimeters [1].