P-Type Doping in Heteroepitaxial CdTe and Lift-Off Technique for Making Thin Film Single Crystal CdTe Solar Cells

Abstract

Epitaxial CdTe(100) layers have been grown on Si(100) by conventional molecular beam epitaxy (MBE) and photo-assisted MBE (PAMBE) using stacked BaF₂-CaF₂ as a buffer. Growth kinetics have been studied with RHEED. The RHEED patterns indicate that in PAMBE, laser illumination induces Te desorption and the Sb-dopants get incorporated at desorbed Te-sites. PAMBE grown layers have superior structural quality compared to the MBE grown layers. The photoluminescence of CdTe:Sb at 10 K shows a single dominant (A°, X) peak at 1.588 eV. The electrical resistivity of CdTe:Sb layer is 1×10³ ohm.cm while that of As-doped is ∼20 ohm.cm. A lift-off technique has been used to separate the single crystal CdTe thin films from the Si wafer by dissolving the fluoride buffer. CdS/CdTe solar cells have been fabricated in these layers.