Carrier transport and recombination in MOVPE-grown CdTe/ZnTe/GaAs and ZnTe/GaAs heterostructures

The carrier dynamics in metalorganic vapour-phase epitaxy-grown CdTe/ZnTe/GaAs and ZnTe/GaAs heterostructures is investigated by transient laser-induced grating (TLIG) spectroscopy. TLIG measurements were performed at room temperature for different grating periods and pump excitation intensities. By best-fitting the slower part of the TLIG decay curves with a one-dimensional model we found recombination lifetime tau(R) = 1130 ps, and carrier diffusion coefficient D = 29.5 cm(2)/s for CdTe/ZnTe/GaAs samples and tau(R) = 1670 ps, D = 31.4 cm(2)/s for ZnTe/GaAs. Whilst the above lifetime values are typical for highly excited II-VI semiconductors, the diffusion coefficients are much higher than that expected for bipolar diffusion. Our D values can be explained by unipolar (n much less than p) diffusion as a result of the efficient trapping of electrons in CdTe and their fast escape into GaAs for ZnTe.