MBE TECHNIQUES FOR IV-VI OPTOELECTRONIC DEVICES

Recent development of high-quality IV-VI optoelectronic devices grown by MBE has significantly increased the technological importance of this epitaxial technique in IV-VI materials. Despite the progress made, much is still unknown about the importance of crystal perfection for device performance. Criteria for crystal perfection required to minimize carrier recombination and optical losses in i.r. devices in IV-VI materials need to be established. In this paper the literature on IV-VI film growth by vacuum deposition techniques is briefly reviewed. MBE techniques used for growth of IV-VI materials on BaF2 and SrF2 substrates and for growth of PbSnTe on PbTe substrates are described. Emphasis is on the techniques used to deposit pseudobinary alloys with homogeneous composition. The use of foreign impurity dopants is also discussed. Criteria of quality and crystal perfection of epitaxial layers needed for device performance are evaluated. In layers grown on IV-VI substrates, large dislocation densities due to lattice mismatch are normally present but may not be detrimental to device performance. Lattice-matched heteroepitaxial system are discussed. For insulating substrates, it is shown that the crystalline quality and the carrier mobility of layers grown on BaF2 and SrF2 are superior to those grown on alkali halide substrates and that the latter are unsuitable for making devices. Carrier mobility is not a good test of crystalline perfection, however, it is argued that device performance, particularly in the demanding requirements for low-noise photodiodes, is a sensitive measure of the epitaxial material quality. Thin-film photodiodes grown by MBE and the hot-wall techniques are then reviewed in detail, including some recent unconventional devices in which the unique properties of thin films are exploited. Heterostructure optical waveguides are described briefly followed by a review of diode laser results obtained by MBE and the hot-wall technique. These results are for thin-film PbTe lasers grown on BaF2 and for a variety of devices grown on I-VI substrates including single heterostructure, double heterostructure, homostructure, and distributed feedback lasers. © 1981.