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The study of lifetimes regarding the recombination of non-equilibrium carriers and their kinetics is essential in order to explain the recombination mechanisms in semiconductors. The study of recombination kinetics and lifetime values in CdSe epitaxial layers is the target of this paper. CdSe layers have been deposited on (0001) mica substrates by vapor epitaxial method. The epitaxial layers contain defects that induce gap states and specific recombination kinetics. The lifetimes were determined by photoconductive frequency-resolved spectroscopy (PCFRS), a usual method for such measurements. The lifetime spectra obtained show in all studied samples the presence of three types of recombinations: τ1 is due to band-to-band recombination, τ2 to surface recombination associated with chemical impurities and τ3 to surface recombination associated with structural defects. The lifetime measured as a function of the substrate temperature denotes a complex correlation between the crystal perfection and the growth temperature.

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The analysis of carrier lifetime distribution in CdSe epitaxial layers grown onto (0001)-oriented mica substrates by the vapor epitaxial method at various substrate temperatures (745°C, 750°C and 780°C), annealed at temperatures up to 400°C and impurified with iodine and chlorine carrier traps is made in the frequency range of carrier recombination kinetics by means of photoconductive frequency-resolved spectroscopy (PCFRS). The carrier lifetime distribution depends on processes related to band-to-band, deep local levels induced by impurities and structural defect recombination mechanisms.

The lock-rn amplifier technique is frequently used in characterization of optoelectronic devices. A digital lock-in amplifier and a digital direct synthesis signal generator are implemented with a general propose 68HC1 1E1FN microcontroller. The resolution in frequency is less than 1 Hz. The digital lock-in amplifier operates over a frequency range from 1 Hz to 1 kHz and can measure signal at any harmonic of the reference signal. Typical error is less than 0.5%for the range of frequencies reported. This thgital lock-in technique is inexpensive and can be used in experiments with low frequency response.