Direct method for the investigation of nonradiative recombination in semiconductors

The dynamics of nonradiative recombination processes are investigated by measuring the thermal expansion and subsequent displacement of a sample surface caused by the absorption of a modulated laser beam. The displacement is detected with a Michelson interferometer for modulation frequencies of 1 Hz–100 kHz. We find that the frequency dependence of the signal is only weakly influenced by thermal or acoustic properties, and therefore solely reflects the dynamics of the nonradiative recombination processes. The feasibility of the method is demonstrated and results from crystalline and amorphous Si are presented.