Minority Carrier Lifetime Measurement by MW-PCD Based on Doppler Effect

In order to measure the minority carrier lifetime of semiconductor, a method of microwave photoconductivity technique (MW-PCD) based on Doppler Effect is used in this paper. By introducing a frequency shifter and a mixer, the high frequency detection signal is modulated and demodulated to be low frequency received signal, which can reduce the performance requirements of the devices in the received end of system. The key technologies about the selection of laser wavelength and microwave frequency, the design of frequency shifter and mixer are studied. The formula contains all related factors in the measuring process is summed. Experiments show that the resultant curves are consistent with the formula highly, confirming the feasibility of the measurement method. The new measurement method can measure the minority lifetime without destructiveness and contact, reduce system cost, improve the signal to noise ratio, and make great sense in optimizing the performance of semiconductor materials.