In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear behavior in the low current range with a slope 1.9 and a sublinear behavior with a slope 0.85 in the high current range are observed.

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We report on fabrication and characterization of blue GaN–InGaN multi-quantum well (MQW) light-emitting diodes (LEDs) over (111) silicon substrates. Device epilayers were fabricated using unique combination of molecular beam epitaxy and low-pressure metalorganic chemical vapor deposition growth procedure in selective areas defined by openings in a SiO2 mask over the substrates. This selective area deposition procedure in principle can produce multicolor devices using a very simple fabrication procedure. The LEDs had a peak emission wavelength of 465 nm with a full width at half maximum of 40 nm. We also present the spectral emission data with the diodes operating up to 250 °C. The peak emission wavelengths are measured as a function of both dc and pulse bias current and plate temperature to estimate the thermal impedance.

Scanning tunneling microscopy is used to study the nonequilibrium surface morphology of singular and vicinal Ge͑001͒ grown by molecular-beam epitaxy. Growth on substrates with Ϸ0.1°miscut produces patterns of nearly symmetrical growth mounds over a wide range of growth temperature, 60ϽTϽ230°C and film thickness, 0.5ϽhϽ1000 nm. The characteristic slope or aspect ratio of the growth mounds increases with film thickness. Analysis of the onset of mound formation gives an estimate of the Ehrlich-Schwoebel length; l ES is approximately equal to the surface lattice constant and independent of temperature. This small value for l ES implies either a weak repulsive barrier (⌬E d ϳk B T) at descending steps or a step-adatom attraction (⌬E a Ͼk B T) at ascending steps. Buffer layers grown at Tϭ365°C on vicinal substrates ͑9°miscut towards ͓110͔͒ show ͑115͒ facets. Low-temperature growth on vicinal surfaces ͑6°and 9°miscuts at Tϭ155 and 230°C͒ produces highly anisotropic growth ridges oriented along the miscut direction with larger roughness amplitude and smaller in-plane length scales than mounds produced by the same growth conditions on singular substrates. At 230°C, the slopes of the growth ridges are stabilized by the ͑105͒ surface.