Lattice strain determination in MOVPE grown ZnTe epilayers on GaAs by RBS-channeling and reflectance spectroscopy

The determination of elastic strain in MOVPE-grown ZnTe epitaxial layers on (100)GaAs by ion channeling Rutherford backscattering spectrometry (RBS) and low temeprature (10K) reflectance spectroscopy is reported in this paper. The crystalline and optical quality of the examined samples is very good as estimated by photoluminescence spectroscopy in conjunction with ion channeling and reflectance measurements. This allowed us to perform meaningful and accurate strain measurements on all investigated samples. The present in-plane strain values obtained by the two techniques are consistent in the range of the epilayer thicknesses examined, showing that the total measured strain increases monothonically with the epilayer thickness. Also, its sign changes from negative (compressive) to positive (tensile) values at around 300 nm. This effect is explained by considering the occurrence of a thickness-dependent residual compressive strain superposed to the expected thermal strain, the latter being caused by the cooling down of the ZnTe/GAs structure from the growth temperature to room temprature