Molecular beam epitaxy of II–VI wide bandgap semiconductors

The paper presents the issues and challenges for molecular beam epitaxy (MBE) of the II–VI wide-bandgap semiconductors used for blue/green lasers. Use of reflection high-energy electron diffraction (RHEED) addresses many of these challenges, permitting characterization and control of various aspects of wide-bandgap II–VI MBE growth. The paper describes their use to control composition of Zn_{1 − x}Mg_xSe and ZnS_ySe_{1 − y}, layers, and to measure and control the growth rates of ZnSe, ZnTe and CdSe during migration-enhanced epitaxy (MEE) growth. RHEED oscillations reveal additional information about growth processes during II–VI MBE. The Mg sticking coefficient is found to be independent of substrate temperature, flux ratios, and electron beam excitation. Re-evaporation of Se, but not of Zn, is found to occur during pauses in growth. The effects of an electron beam on growth may be quantitatively determined.