Precise Measurements of Transient Excess Carrier Lifetimes in II-VI Films and Superlattices

Abstract

ABSTRACTA system has been developed for accurately measuring lifetimes for photo-induced excess current carriers in semiconductors using the transient photoconductivity decay method. The specifications of state-of-the-art equipment, considerations peculiar to the capture of fast transient pulses, and sophisticated statistical data analysis techniques are discussed. Experimental results are presented to demonstrate the capability of the system (a) to measure lifetimes in the 40-ns - 75-µs range for temperatures varying from 77K to 300K with 10% accuracy for single lifetime decays and 30% accuracy for individual effective lifetimes in a multi-component decay, and (b) to use a 300-ns lifetime photoconductor as a detector to measure nanosecond-time-scale structure of laser pulses. The predominant excess carrier lifetimes of HgCdTe samples grown at NCSU by photoassisted molecular beam epitaxy (PAMBE) ranged from 46 ns at 300K to 341 ns at 77K. CdTe samples and CdMnTe-CdTe superlattices exhibited a multi-component decay with the two longest components having effective lifetimes of 26 µs and 4 µs for CdTe and 75 µs and 10 µs for CdMnTe-CdTe. These values were relatively insensitive to temperature variation.