GROWTH AND CHARACTERIZATION OF LIGHT-EMITTING ZNS GAN HETEROSTRUCTURES/

Heterostructures involving ZnS/GaN show promise for the injection of h oles from p-GaN into n-ZnS. Utilizing knowledge obtained from ZnS phos phor technology, this combination could result in a new type of multi- color electroluminescent display. Further, this combination provides a very interesting interface. Both ZnS and GaN are very ionic materials . Hence, it is desirable that the interface will be relatively benign, and that charge injection can occur despite the large lattice mismatc h and resulting misfit defects that form near the interface. The highl y lattice mismatched structures ZnS/GaN and ZnS/Al2O3 were grown by mo lecular beam epitaxy using elemental sources. Growth rates of up to 0. 4 mu m ph were observed for the lower growth temperatures, with rapidl y diminishing rates for temperatures above 350 degrees C. The GaN subs trate consisted of a 3 mu m epilayer grown on sapphire (0001) by metal organic chemical vapor deposition. Reflection high energy electron dif fraction observations indicate that the zincblende ZnS layers commonly contain (111) twins, although films with no visible twin spots could be grown at a high substrate temperature. The sulfide layers were char acterized using photoluminescence, x-ray diffraction, and scanning ele ctron microscopy (SEM). X-ray peaks typically had widths of 400 arcsec for omega/2 theta scans, and somewhat worse for omega scans, indicati ng mosaic tilt. Photoluminescence spectra of the ZnS films doped with Ag and Al demonstrated the characteristic blue transition near 440 nm. SEM electron channeling patterns indicated that the ZnS films lie at a 30 degrees rotated orientation to the Al2O3 (0001) substrate, as doe s GaN. p-GaN/n-ZnS devices were fabricated using standard photolithogr aphy techniques. The current voltage characteristics are reported and preliminary electroluminescence results are discussed for this heteroj unction system. (C) 1997 American Vacuum Society.