Growth of epitaxial CdTe/CdS heterostructures for single crystal thin film solar cell applications

Epitaxial CdTe/CdS heterostructures have been grown by molecular beam epitaxy onto BaF₂ covered Si (111) substrates. An epitaxial BaF₂ buffer is used for compatibility reasons, and because of easier dissolution during the lift-off processing. Epitaxy of cubic CdS (111) layers on BaF₂/Si (111) is achieved; electron channelling patterns exhibit a three-fold symmetry which is a characteristic for cubic crystal structures. The growth kinetics and structural properties of epitaxial CdS and CdTe/CdS have been studied with reflection high energy electron diffraction, Rutherford backscattering spectrometry and X-ray diffraction rocking curve measurements. The full width at half maximum of the (222) CdS and (333) CdTe X-ray peaks are ~1150 arcsec for 2.7 and 3.4 μm thick CdS and CdTe layers, respectively. To fabricate CdTe/CdS single crystal thin film solar cells, a lift-off process has been developed to remove the epitaxial layers from the Si substrates