Interfacial nucleation of compounds for thin-film Co-Hg1−xCdxTe contacts

Abstract

We have determined the phases formed at the interfacial contact between deposited Co thin films prepared with both e-beam evaporation and sputtering of Co onto CdTe (111) and Hg0.8Cd0.2Te substrates using transmission electron microscopy and diffraction. Sputter profiling with Auger electron spectroscopy has been used to determine the depth profiles of Co, Cd, Te, and Hg at the interface and throughout the Co overlayer on Hg0.8Cd0.2Te and CdTe. For the Co-Hg0.8Cd0.2Te system, the γ phase is formed upon sputter deposition of Co films of 80 Å or thicker at room temperature. This Co-Te phase is also seen for thinner films upon annealing (e.g., 100 °C for a 40-Å Co film) after sputter deposition. However, after the deposition of 80-Å Co by e-beam evaporation onto an Hg0.8Cd0.2Te substrate, the γ phase forms only after annealing at 150 °C in vacuum. Texturing of the γ phase was observed in the transmission electron diffraction patterns with the Hg0.8Cd0.2Te substrates, indicating at least a partial ordering of this phase with respect to the substrate. On the CdTe substrates, Te was observed after Co deposition in either deposition system. The Te generated by either sputter deposition or e-beam evaporation with a high deposition rate (8–10 Å/s) of Co onto CdTe (111) was polycrystalline, whereas the slow deposition rate (0.3–0.5 Å/s) e-beam evaporation resulted in amorphous Te. Auger electron spectroscopy results indicated that the Te generated is distributed throughout the Co film. The Co-Te γ phase was formed upon annealing at 300 °C after sputter deposition and at 350 °C after e-beam evaporation, but the crystallites did not have the relationship to the substrate (texturing) which was displayed by those on the Hg0.8Cd0.2Te substrates. Annealing of the Co overlayer on Hg0.8Cd0.2Te causes the growth of the crystals and an increase in ordering of the γ phase.