Masakazu Kobayashi
Department of Electrical Engineering and Bioscience
Waseda University, Tokyo Japan

Growth of severely lattice mismatched materials is always difficult, but the success could open a glorious future. In this context, MBE growth and characterization of two different materials combinations would be discussed. They are namely the rock salt structure SnTe layer growth on zincblende structure GaAs substrates and zincblende structure ZnTe layer growth on “hexagonal” Al2O3 substrates.

High temperature thermal treatment of Al2O3 substrates produces atomically flat surfaces or nano-facet structures. The orientation of the successively grown ZnTe layers were drastically affected by the direction of the substrate surface orientation as well as the surface treatment conditions.
(100) oriented layer of SnTe can be grown on (100) oriented GaAs substrate, but (111) layers can be also grown on (100) substrates. SnTe (100) single-domain thin films have been previously grown on GaAs substrates by molecular beam epitaxy but obtaining excellent crystallinity can be difficult. ZnTe buffer layers are introduced to improve the crystallinity of SnTe films. The effects of the molecular beam flux ratio (JTe/JSn) and growth temperature (Tg) on the crystallinity are investigated to achieve high-quality layers. The surface morphology and electrical properties of the SnTe thin films are also evaluated in addition to the conventional X-ray diffraction measurements. The crystallographic properties of the grown samples are shown to be significantly improved by introducing a ZnTe buffer layer. It is also found that lowering JTe/JSn to 0.6 results in a reduced growth rate, and an increased growth temperature (Tg = 220 °C) promotes the migration of atoms at the growth front. compares the θ-2θ scan and the pole figure images of a layer grown with the ZnTe buffer layer. The θ-2θ scan indicated that the layer included (001), (011), and (111) oriented crystals. (111) oriented crystal was very weak compared to others. However, the pole figure images are relatively different, and strong signals originated from (111) crystal were confirmed while (001), and (011) crystals were less pronounced. The XRD pole figure could tell the detail structural information of the thin films, while the θ-2θ scan provide the information viewed from only one particular direction. The variation of the crystal’s structures which could be observed for the severely lattice mismatched heteroepitaxial layer could be precisely understood by this powerful method.

This work was supported in part by a Waseda University Grant for Special Research Projects and was partly carried out at the Joint Research Center for Environmentally Conscious Technologies in Materials Science at ZAIKEN, Waseda University.