We report results of our growth and characterization of GaN films using low-pressure chemical vapor epitaxy with a new nitrogen source, hydrazoic acid (HN3). This growth technique allows for low-temperature deposition, low III/V ratios, and increased deposition rates (up to ∼2–3 μm/h). The deposited films show Ga:N atomic ratios of 1±0.25 based on our x-ray photoelectron spectroscopy analyses, and the He(II) UPS (ultraviolet photoelectron spectroscopy) spectra compare favorably with the semi-ab initio calculations for the GaN valence bands and with the reported UPS data for single crystal GaN films. X-ray and Raman spectra show deposited films crystallized in the expected wurtzite structure. We find these epitaxial films to be efficient light emitters in the blue or yellow region of the spectrum, depending upon growth conditions. Our photoluminescence time-decay kinetics confirm the excitonic nature of the blue emission. Lastly, far infrared time-domain spectroscopy shows the low carrier concentration of this material.

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An emission, named (D 2 0 ,X), located at ϳ3.48 eV at low temperature, in the near-band-edge spectrum of GaN, was investigated by photoluminescence ͑PL͒. This (D 2 0 ,X) emission is close in energy to the well-studied neutral-donor-bound-exciton (D 0 ,X) line in GaN. They are distinguished by a variety of PL measurements in this study. Excitation power and temperature-dependent studies indicate that this emission is related to a bound exciton complex. Annealing at a relatively low temperature ϳ440°C results in a dramatic reduction of the PL intensity of this emission. A model is proposed that the exciton-binding center responsible for the (D 2 0 ,X) emission consists of a ͑shallow͒ donor-hydrogen complex that is formed in the GaN epilayer during the growth. The annealing at 440°C results in the dissociation of this complex and thus reduces the PL intensity of the (D 2 0 ,X) emission.

We have grown high-quality GaN films on sapphire using a new nitrogen precursor, hydrazoic acid ͑HN 3 ͒. Films were grown at 600°C on ͑0001͒ sapphire substrates in a low-pressure chemical-vapor-deposition system using triethylgallium and hydrazoic acid as precursors. Subsequently, we have conducted a complete study of the surface, structural, electrical, and optical properties of these GaN films, and our early results are very encouraging. All films were of wurtzite crystal structure, slightly polycrystalline, and n type at about 2ϫ10 17 cm Ϫ3 . We find the films to be efficient light emitters in the near-band edge region of the spectrum. Analysis of the emission energies and kinetics suggests that the midgap emission results from a superimposed deep-donor-to-shallow-acceptor emission and a deep-donor-to-valence-band emission, where the deep donor consists of a distribution of energy levels, thereby yielding a broad emission band.

The dissociation channels of two prominent bound exciton complexes in wurtzite GaN thin films are determined via an extensive temperature dependent photoluminescence study. The shallow donor bound exciton dissociation at low temperatures (T ≤ 50 K) is found to be dominated by the release of a free exciton with thermal activation energy consistent with the exciton localization energy. At higher temperatures a second dissociation channel with activation energy E A = 28 ± 2 meV is observed. The dissociation of a bound exciton complex with exciton localization energy E X loc = 11.7 meV is also dominated by the release of a free exciton. In contrast to previous studies evidence is presented against the hypothesis of this emission being due to the exciton bound to an ionized donor. We find that it originates most likely from an exciton bound to a neutral acceptor.