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GaN nanopillar and nanostripe arrays with embedded InGaN/GaN multi-quantum wells (MQWs) are fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures is successfully healed through annealing of NH3/N2 mixtures under optimized conditions.

Rotational Maker fringes were used to measure the non-linear susceptibilities chi[(super 2)(sub 31)] and chi[(super 2)(sub 33)] for a series of metalorganic chemical vapor deposition (MOCVD) and hydride vapor-phase epitaxy (HVPE) AlxGa1-xN thin-film samples grown on sapphire substrates. The results are consistent with theoretical studies of nonlinear susceptibilities for GaN and AlGaN.

The metalorganic chemical vapor deposition of gallium nitride on Si(111) is examined in terms of stress control and application to field-effect transistors.

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

The effect of subband gap illumination on transport properties of AIGaN/GaN heterostrcutures was investigated using the Shubnikov-de Haas and Hall effects.

The fabrication of junction field effect transistors on a GaN epitaxial structure grown by metal organic chemical vapor deposition is discussed.

Results demonstrate that the thin AlGaN and thick GaN layers are coheretly strained as determined by x-ray diffraction map analysis. Data on mobility spectra reveal single-carrier transport at low temperatures.

Thin A1xGa1-xN layers grown by metalorganic chemical vapor deposition, were studied.

Research was conducted to examine the formation of the two-dimensional electron gas (2DEG) in AlGaN/GaN structures grown by plasma-assisted molecular-beam epitaxy. The low-temperature electron transport and charge transfer in the AlGa/Ga structures were studied as a function of the Al(sub x)Ga(sub 1-x)N barrier composition and its width. Results may be related to the change in the alloy disorder scattering or interface roughness scattering that substantially intensify as the density of the 2DEG increases.

Research was conducted to examine the surfaces of GaN films deposited by metalorganic chemical vapor deposition and molecular beam epitaxy using atomic force microscopy. The objective was to explain how the surface structures form and how they can be controlled. Results demonstrate that the spiral hillock formation was dependent on the critical radius of curvature of the step-line and the miscut terrace width.

The first inclusion of GaAs in the pores of MCM-41 is reported. Of special concern is the optical characterization of a direct-gap semiconductor heterostructure synthesized by deposition of GaAs into the channels of MCM-41 using metalloorganic chemical vapor deposition. The GaAs/MCM-41 heterostructures exhibit blue-shifted absorption and broad visible photoluminescence even at room temperature. The MCM-41 pore diameter determines the photoluminescence, thus supporting formation of size-quantized semiconductor crystallites whose growth is restricted by the diameter of the pores of MCM-41.

A study was conducted on the structure, morphology and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy. The findings indicate that GaN layers grown with a low III/V ratio exhibited a faceted morphology and a tilted columnar structure with a high density of stacking faults. On the other hand, films grown with a high III/V ratio exhibited comparable structure to the underlying MOCVD-grown template.

Experimental magnetic field dependent Hall and resistivity data is presented for two modulation-doped AlGaN/GaN heterostructures in the temperature range from 6 to 300 K and for a magnetic field up to 12 T. An analysis of the temperature dependencies of mobility and electron concentration in the GaN layer and two-dimensional electron gas indicates that electron transport in the GaN layer is dominated by carriers in the conduction band for the case of low-doping (10 super 18 per cu cm).

Polarized photoreflectance (PR) spectroscopy is used to investigate a [1120]- oriented A-plane GaN film on R-plane sapphire, where the c axis of GaN lies in the film plane. The results indicate that the observed transition energies and polarization properties of the three transitions can be used to describe the presence of an overall compressive, anisotropic in-plane strain in the film.

Two-dimensional reciprocal space mapping of high resolution x-ray diffraction was utilized to examine the structural properties of InGaN/GaN/AlGaN multiple quantum wells (MQW). It was found that the InGaN/GaN/AlGaN MQWs are grown coherently on the GaN base layer. Better interface properties were achieved with Si doping. Results indicated that Si doping in the GaN barriers influences the interface quality of the InGaN/GaN MQW systems.

Monoenergetic positron beam is used for probing the vacancy-type defects in AlN grown by metal-organic vapor phase epitaxy (MOVPE) and lateral epitaxial overgrowth (LEO) using halide vapor phase epitaxy. Doppler broadening spectra of the annihilation radiation are measured and compared to the spectra calculated by using the projector augmented-wave method.

Smooth N-polar InGaN/GaN and AlGaN/GaN multiquantum wells (MQWs) and heterostructures are grown by metal organic chemical vapor deposition on (0001) sapphire substrates with misorientation angles toward the a-sapphire angle. The studies have shown that the tendency toward formation of multiatomic steps at the film surface and at interfaces has increased with increasing misorientation angle.

The properties of GaN/[Al.sub.x][Ga.sub.1-x]N/GaN heterostructures with a different Al mole fraction and Si doping in the barrier layer and fabricated devices from selected wafers are examined. The fabricated devices have displayed a drain-source current of 0.9 A/mm at a gate-source voltage +1 V.

Scanning capacitance microscopy is used for characterizing nanoscale, local electronic structure in nonpolar n-type GaN grown in the a-plane orientation by using lateral epitaxial overgrowth (LEO). The studies have shown that the positive charge associated with the defect is very significant, as linear defects like threading dislocations in c-plane n-GaN are nearly universally observed to be either electrically neutral or negatively charged.

Smooth, high quality N-polar GaN films are grown by metal organic chemical vapor deposition (MOCVD) on misoriented sapphire substrates by using a high temperature nucleation process. The studies have shown that the quality of the N-polar GaN films deposited (0001) sapphire substrates with a misorientation angle is comparable to Ga-polar GaN-on-sapphire films grown in the same reactor.

The forward biased current-voltage-temperature (I-V-T) and internal photoemission measurements were used to investigate the impact of threading dislocation density on Ni/n-GaN Schottky barrier diode characteristics. A simple model that reconciles both the shift and variations in the extracted Richardson constant as a function of threading dislocation density is presented.

P-n junctions formed by selective regrowth of n-(Al)GaN on p-GaN is characterized by I-V measurements and secondary-ion mass spectrometry (SIMS). Regrown p-n diodes of high quality with low leakage currents is achieved, comparable to as-grown GaN p-n diodes, by optimizing the regrowth conditions and structures.