Magnetic Resonance Studies of Mg-Doped GaN Epitaxial Layers Grown by Organometallic Chemical Vapor Deposition
NAVAL RESEARCH LAB WASHINGTON DC
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Electron paramagnetic resonance EPR and optically detected magnetic resonance ODMR experiments have been performed on a set of GaN epitaxial layers doped with Mg from 2.5 x 10exp 18 to 5.0 x 10exp 19cu cm. The samples were also characterized by secondary-ion-mass spectroscopy SIMS, temperature-dependent Hall effect, and low-temperature photoluminescence PL measurements. EPR at 9 GHz on the conductive films reveals a single line with gsub parallel approx. 2.1 and gsub perpendicular approx. 2 and is assigned to shallow Mg acceptors based on the similarity of the spin density with that found for the number of uncompensated Mg shallow acceptors from Hall effect and the total Mg concentration by SIMS. PL bands of different character are observed from these layers, including shallow-donor shallow-acceptor recombination at 3.27 eV from the lowest doped sample and, in most cases, broad emission bands with peak energy between 2.8 and 3.2 eV from the more heavily doped films. In addition, several of the films exhibit a weak, broad emission band between 1.4 and 1.9 eV. ODMR at 24 GHz on the blue PL bands reveals two dominant features. The first is characterized by gsub parallel, gsub perpendicular approx. 1.95-1.96 GHz and is assigned to shallow effective-mass donors. The second line is described by similar g tensors as found by the EPR experiments and, thus, is also attributed to shallow Mg acceptors. Although several groups have related the 2.8 eV PL in heavily Mg-doped GaN with the formation of deep donors, no clear evidence was found from the ODMR on this emission for such centers. However, based on the near-midgap PL energy and the observation of the feature assigned to shallow Mg acceptors, the strongest case from magnetic resonance for the existence of deep donors in these films is the isotropic ODMR signal with g2.003 found on emission 1.9 eV.
- Industrial Chemistry and Chemical Processing
- Inorganic Chemistry
- Atomic and Molecular Physics and Spectroscopy