Spectroscopic study of CdTe layers grown by molecular-beam epitaxy on (001) and (111) Cd0.96Zn0.04Te substrates

Abstract

The optical properties of CdTe grown by molecular-beam epitaxy are investigated by means of high-resolution photoluminescence, reflectivity, transmission, and resonant excitation spectroscopy. The CdTe epilayers are grown on (001)- and (111) B-oriented Cd0.96Zn0.04Te substrates. Sharp and strong lines associated with impurity bound exciton recombination dominate the spectra and indicate a good crystalline quality as well as a low level of impurity contamination. For the donor bound exciton lines, two electron transitions are observed which allow an identification of the chemical nature of the donors (probably Ga) by comparison with the data previously obtained on bulk material. For the acceptor lines, however, the shallow states which contribute to the spectra are different from those reported in the bulk and seem correlated with more complex centers. This study also reveals the importance of the residual strain contribution. Moreover, the marked difference observed for the optical properties between the (001) and the (111) epilayers spectra clearly evidence the change in the incorporation rate of impurities and/or grown-in defects density with the growth direction. The best spectra are obtained for the (001)-oriented CdTe layers.