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The strain dependence of the free-exciton resonance energies in AlN epilayers and the values are analyzed by using an appropriated Hamiltonian assuming equibiaxial stress for the wurtzite crystal structure in order to obtain valence band parameters. The strain dependence of the valence band ordering, optical transition probability and free-exciton binding energy are analyzed.

The electrical and structural characterization of Mg-doped Al-rich p-type [Al.sub.0.69][Ga.sub.0.31]N alloys on SiC substrate grown by metal organic chemical vapor deposition is presented. Transmission electron microscopy has shown the generation of vertical spike-like defects with increasing Mg doping and the increase in resistivity with the increase in Mg doping.

The adsorption and subsequent desorption of Ga on (0001) GaN using simultaneous line-of-sight quadrapole mass spectroscopy (QMS) and reflection high-energy electron diffraction (RHEED) is investigated. It is concluded that the experimental results show the complementary nature of the information provided by the RHEED oscillations and the Ga-adlayer coverage measured by QMS.

A new study seeks to advance growth and fabrication technology for GaN HBTs.

Several analyses are conducted to explain the mechanisms involved in the polarity inversion occurring because of the insertion of an aluminum oxide interlayer on the N-face GaN. The inversion is shown to lead to smoother surfaces and enhanced electrical properties in the materials.

The plasma-assisted molecular beam epitaxy technique is employed to analyze the nucleation of islands observed on the continuous high-quality [In.sub.2][O.sub.3](001) films. The growth of the bulk of the film on the nucleation layer is shown to lead to a higher crystalline quality.

The impact of growth conditions, including temperature and the group-III flow rates, on the surface morphology and indium mole fraction were studied for [In.sub.x][Al.sub.1-x]N layers grown on GaN on both the In-polar and N-polar orientations. The indium incorporation increased with decreasing growth temperature and increasing growth rate for both In-polar and N-polar layers.

As-grown and oxygen plasma treated n-type tin dioxide (SnO2) (101) thin films were examined to understand the properties of Au contacts, surface structure, and band bending. The damaged layer due to oxygen ion bombardment, oxygen adsorption layer, and possibly bulk traps depleted the surface carriers facilitated the formation of a Schottky contact with Au.

Two-dimensional optical waveguide mode simulations are used for examining the optimized device structures for ridge-waveguide (Al, In, Ga)N-based green laser diodes (LDs). The studies have shown that regarding the effect of Mg doping concentration on the absorption, the reduction in Mg in the p-cladding layer and the p-guiding layer is vital to reduce waveguide absorption ([alpha]).

The polarity of GaN grown by plasma-assisted molecular beam epitaxy is inverted from N-face to Ga-face by simultaneously exposing the surface to Mg and activated N fluxes during a growth interruption at a reduced substrate temperature. Current-gain cutoff and maximum oscillation frequencies are measured and the device performance is similar to that of Ga-face transistors with comparable dimensions.

Smooth, high-quality N-polar GaN films are grown on C-face SiC substrates by metal organic chemical vapor deposition (MOCVD) and their structural and morphological properties are characterized. An island growth mode is seen for the initial layer of GaN, which has described the strong correlation of the growth temperature of the initial GaN layer to the film quality.

The Si[N.sub.x]/GaN interface barrier height for N-polar GaN based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) is examined. The Fermi level at the interface is pinned at approximately 1 eV with respect to GaN conduction band edge and Hall measurements of the two-dimensional electron gas density have corroborated the predicted interface barrier height.

The development of N-polar GaN-based high electron mobility transistors grown by [N.sub.2] plasma-assisted molecular beam epitaxy on C-face SiC substrates is described. An AlGaN-cap layer is used for reducing gate leakage in these devices and for achieving a low-dispersion high breakdown voltage device.

The Ga-adlayer mediated growth of GaN quantum dots at 707 degree Celsius on AlN (0001) by simultaneous use of in situ reflection high-energy electron diffraction and line-of-sight quadrupole mass spectrometry during rf-plasma assisted molecular beam epitaxy (PA-MBE) is investigated. The results reveal that the Ga-adsorbate coverage of 1.0 ML (monolayer) is critical in the mediation of a fundamental change in the GaN Stanski-Krastanov (SK) growth mode on AIN.

Achieving nitride-based device structures unaffected by polarization-induced electric fields is realized with nonpolar GaN. Analysis of the lateral epitaxial overgrowth stripes shows that (0001) surfaces grow faster than (000bar1) surfaces by approximately an order of magnitude.

A comprehensive study of Al0.32Ga0.68N/GaN and GaN/Al0.32Ga0.68N/GaN heterostructures is reported. A surface Fermi-level pinning position of 1.7 eV for AlGaN and 0.9-1.0 eV for GaN, and an interface polarization charge density of 1.6*10(13 to the power of 10)-1.7*10(13 to the power of 10) cm(super -2), are extracted from the simulations.