Low Schottky barrier height contacts to n-CdTe using rare-earth metals

Abstract

Low-resistance contacts on n-type CdTe have been produced by molecular-beam epitaxy using metallic rare earths (europium, samarium, and neodymium). The metallic europium and neodymium epitaxy is achieved via an interfacial layer about 3 nm thick which results from the strong reactivity between the rare-earth metal and the tellurium semiconductor anion. For the two-dimensional growth of europium the interfacial layer is deliberately formed with samarium or neodymium, whereas for neodymium epitaxial growth the interfacial layer is formed with neodymium. Schottky barrier heights of the different heterostructures are determined by current–voltage characteristics and the specific contact resistance is measured using the transmission line model. The best results are obtained for neodymium/n-CdTe heterostructures with a specific contact resistance of 8×10−4 Ω cm2 for a doping level of 4×1017 cm−3. The Schottky barrier heights have been determined to be about 0.35±0.05 eV for the various rare-earth/n-CdTe heterostructures. The temperature and the doping level dependence of the current–voltage characteristics suggests furthermore that a dipolar layer is present at the interface.