CdTe and CdTe/PbTe layers were grown on cleaved BaF2 (111) substrates by molecular beam epitaxy technique employing PbTe, CdTe, and Te2 effusion cells. The growth of the layers was monitored in-situ by RHEED diffraction technique. Crystal structure was examined by standard X-ray diffraction method. The CdTe/PbTe layers are monocrystalline with (111) crystal orientation and exhibit x-ray rocking curve FWHM parameter of 200-300 arcsec for PbTe and 300-600 arcsec for CdTe. The well defined streaky RHEED diffraction pattern was observed during the entire process of growth of both layers indicating a two-dimensional mode of growth with a smooth transition between PbTe and CdTe evidenced by a distinct surface reconstruction.
For the optical characterization of CdTe layers, the photoluminescence spectra were studied at T=4.2 K in 750-870 nm (1.40-1.65 eV) spectral range using pulsed excitation at 2.35 eV by YAG laser. In CdTe/BaF2 (111) layers, the dominant photoluminescence peak is observed at 785 nm and corresponds to the radiative recombination of excitons bound to neutral acceptors. In CdTe/PbTe/BaF2 (111) heterostructures with thick PbTe buffer, no photoluminescence is observed in the spectral rage studied. It agrees with recent photoluminescence studies of PbTe/CdTe/GaAs (100) epilayers [1], and supports the idea that despite the dramatic differences in electronic structure of CdTe and PbTe these semiconductors form type-I quantum well heterostructures with fundamental optical transitions expected in PbTe well in the mid-infrared.
[1] K. Koike et al, J. Crystal Growth 257 (2003) 212. |