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.
A phenomenological theory describing the exciton photoluminescence ͑PL͒ kinetics in type-II superlattices is proposed herein, which takes into account both the intrinsic exciton radiative decay and nonradiative decay due to exciton trapping by interfacial defects surrounding a ''disordered'' interface. We have thus investigated the effect of system dimensionality on details of these nonradiative-decay kinetics. For effectively threedimensional and two-dimensional structures, the theory predicts a transition from strongly nonexponential to nearly exponential decay kinetics as the temperature is increased. Contrastingly, for one-dimensional structures the decay kinetics is predicted to be nonexponential at all temperatures. Using these predictions, we have applied this model to explain our observed time-resolved PL on specific short-period type-II GaAs/AlAs superlattices. These PL decays are thus explained both over a wide range of temperatures ͑2-30 K͒ and over an observed crossover from nonexponential to exponential behavior. The model allows us to extract a nonradiative-defect density and an average radiative-decay rate from the experimental data.
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.
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