High-resolution X-ray diffraction studies on mbe-grown p-ZnTe/n-CdTe heterojunctions for solar cell applications

Abstract

High-resolution X-ray diffractometer was used to study structural quality, lattice parameters and mis-t strain in p-ZnTe/n-CdTe heterojunctions grown by the molecular-beam epitaxy technique on two different (001)-oriented substrates of GaAs and CdTe. The X-ray diffractometer results indicate that the CdTe layers, grown on lattice mismatched GaAs substrate, are partially relaxed, by the formation of mis-t dislocations at the interface, and display residual vertical strain of the order of 10-4 . The presence of threading dislocations in the layers effectively limits the e-ciency of solar energy conversion in the investigated heterojunctions. Homoepitaxially grown CdTe layers, of much better structural quality, display unexpected compressive strain in the layers and the relaxed lattice parameter larger than that of the substrate. Possible reasons for the formation of that unusual strain are discussed.