Reflectivity and absorption of thin ZnTe epilayers near the exciton-polariton
The authors have studied the exciton absorption of single-crystalline ZnTe epilayers grown by metalorganic vapour-phase epitaxy on (001) GaAs substrates. More than 1 mu m of the 2 mu m thick layers, including a dislocation-rich interface region, has been removed by a chemical etching procedure. Transmission and reflectivity measurements have been performed on the same samples with thicknesses below 1 mu m. Samples glued on a glass substrate reveal two exciton absorption structures, which are identified to be the n=1 heavy- and light-hole excitons. This splitting nearly disappears for free-standing layers. The absorption maximum appears at the transverse exciton energy, which has been determined by a polariton model for the reflectivity. The deformation potentials obtained from hydrostatic pressure measurements and from the shift and splitting of the exciton are a=-5.5 eV and b=-1.4 eV at low temperatures.