Shallow Donors In GaN Research Articles

Shallow donors in GaN: A magnetic double resonance investigation

The residual shallow donor in GaN is investigated by electron spin resonance and the Overhauser shift double resonance technique. From the resolved quadrupolar splitting, we determine the electric field gradients at the Ga and the N site. The hyperfine interaction, as determined simultaneously from the Overhauser shift and the Knight shift, supports a delocalized donor wavefunction with an effective Bohr radius of 20–30 Å.

Exciton fine structure in undoped GaN epitaxial films.

We report on photoluminescence experiments on hexagonal GaN epitaxial films grown by hydride and organometallic vapor phase epitaxy on sapphire and 6H-SiC. At low temperatures we observe free and bound exciton recombinations, which allow us to establish the free-exciton binding energy and the localization energies of the excitons bound to neutral donors in undoped films. We demonstrate that the energetic positions of the excitonic recombination lines depend on the layer thickness and the substrate materials on which the layer was deposited. The influence of strain on the valence-band splittings can be quantified when observing the free-exciton transitions onto the different valence bands. The experimental results are compared to a theoretical calculation using a first-principle total-energy pseudopotential method within the local-density formalism. We present evidence for the existence of two shallow donors in GaN. One of them most likely stems from an intrinsic defect. \textcopyright{} 1996 The American Physical Society.

Shallow donors in GaN—The binding energy and the electron effective mass

Fourier transform infrared absorption spectroscopy has been performed on a GaN epitaxial film grown by the hydride vapor phase epitaxy on sapphire substrate. We observe a transition at 215 cm −1 with a half width of 2 cm −1, which we attribute to an electronic transition on the basis of temperature dependent measurements. We assign it to the 1s-2p transition of the residual shallow donors. Using effective mass theory neglecting anisotropies in the effective mass and dielectric constant the binding energy of the shallow donors is calculated to be (35.5 ± 0.5) meV. The electron effective mass is (0.236 ± 0.005) m o. Based on this knowledge, the energy separation between the donor-acceptor and the band-acceptor transitions as seen in photoluminescence at 45 K can be used to evaluate the donor concentration in the epitaxial films.

The influence of TMA and SiH 4 on the incorporation rate of Ga in Al xGa 1− xN crystals grown from TMG and NH 3

In an atmospheric pressure vertical reactor, with conditions designed to minimize predeposition of A1N (water-cooled walls), the growth rate of Al x Ga 1− x N grown from the TMG, TMA and NH 3 decreases rapidly with substrate temperatures above 900°C. The aluminum mole fraction of these films increases with temperatures above 1000°C with other growth parameters fixed. Furthermore, the Ga incorporation rate decreases with increasing TMA input flux at fixed TMG input flux and substrate temperature. A surface kinetic model in which both A1 and Ga compete for the same surface sites and the thermally ativated desorption of Ga from the surface plays a key role has been developed to explain these results. Addition of small amounts of SiH 4 (Si is a shallow donor in GaN) strongly reduces the incorporation rate of Ga but it does not affect that of A1.