Hafnium dioxide films have been deposited using reactive electron beam evaporation in oxygen on hydrogenated Si(100) surfaces. The capacitance–voltage curves of as-deposited metal(Ti)–insulator–semiconductor structures exhibited large hysteresis and frequency dispersion. With post-deposition annealing in hydrogen at 300 °C, the frequency dispersion decreased to less than 1%/decade, while the hysteresis was reduced to 20 mV at flatband. An equivalent oxide thickness of 0.5 nm was achieved for HfO2 thickness of 3.0 nm. We attribute this result to a combination of pristine hydrogen saturated silicon surfaces, room temperature dielectric deposition, and low temperature hydrogen annealing.

Controlled and reproducible growth of GaN nanowires is demonstrated by pulsed low-pressure metalorganic chemical vapor deposition. Using self-assembled Ni nanodots as nucleation sites on (0001) sapphire substrates we obtain nanowires of wurtzite-phase GaN with hexagonal cross sections, diameters of about 100nm, and well-controlled length. The nanowires are highly oriented and perpendicular to the growth surface. The wires have excellent structural and optical properties, as determined by x-ray diffraction, cathodoluminescence, and Raman scattering. The x-ray measurements show that the nanowires are under a complex strain state consistent with a superposition of hydrostatic and biaxial components.

Selective area epitaxy has been used to grow pyramidal GaN stripes, followed by InGaN multiple quantum well (MQW) structures, in order to produce long-wavelength green light emission. Stripes oriented along ⟨112¯0⟩ produce smooth {11¯01} sidewall facets. The room-temperature optical properties are investigated by cathodoluminescence spectroscopy using a scanning electron microscope. MQWs grown in unmasked reference regions exhibit emission at 450 nm. The stripe sidewalls emit light with peak wavelength of 500 nm with consistent linewidth and intensity. The stripe ridge emits light with peak intensity at wavelength of ∼550 nm. Based on the spatial extent of the 550 nm emission, the ridge is estimated to be ∼250 nm wide. The large redshift is produced by the enhanced presence of indium species due to lateral vapor diffusion and surface migration in selective area epitaxy.

We describe solar-blind photodetectors based on superlattices of AlN/AlGa(In)N. The superlattices have a period of 1.4 nm, determined by x-ray diffraction, and an effective band gap of 260 nm measured by optical reflectivity. Using simple mesa diodes, without surface passivation, we obtain low dark leakage currents of 0.2–0.3 pA, corresponding to the leakage current density of ∼0.3 nA/cm2, and high zero-bias resistance of ∼1×1011 Ω. Excellent visible cutoff is obtained for these devices, with six orders of magnitude decrease in responsivity from 260 to 380 nm. These results demonstrate the potential of junctions formed by short-period superlattices in large-band-gap devices.

We report a systematic study of the optical properties of superlattices of AlN/Al 0:08 Ga 0:92 (In)N with periods in the range of 1.25-2.25 nm. The superlattices were grown on sapphire substrates using gas source molecular beam epitaxy with ammonia. Effective bandgaps between 4.5 eV (276 nm) and 5.3 eV (234 nm), as determined by optical reflectivity measurements, were obtained by adjusting the barrier and well thickness. These superlattices can be doped n-and p-type. We demonstrate double heterostructure light emitting diodes operating at wavelengths as short as 262 AE 2 nm.