Articles you may be interested inEffect of annealing on metastable shallow acceptors in Mg-doped GaN layers grown on GaN substrates Appl. Phys. Lett. 92, 151904 (2008); 10.1063/1.2909541Desorption of InSb(001) native oxide and surface smoothing induced by low temperature annealing under molecular hydrogen flowWe report a systematic study of the effects of wet chemical treatment, inductively coupled plasma etching, and thermal annealing on the surface and optical properties of Mg-doped p-type GaN. The chemical bonding and surface stoichiometry of the GaN surface subjected to different processing steps are analyzed based on the results of x-ray photoelectron spectroscopy. Atomic force microscopy has been employed to characterize the surface morphology. Photoluminescence ͑PL͒ and micro-Raman techniques have been used to investigate the electronic and vibrational properties of plasma etched surface. We have correlated the surface changes induced by dry etching of p-type GaN to the corresponding changes in the defect and impurity related states, through their manifestation in the PL spectra. We have observed several local vibrational modes ͑LVMs͒ in p-type GaN subjected to various processing steps. A broad structure in the low-temperature Raman spectra around 865 cm Ϫ1 is attributed to the electronic Raman scattering from neutral Mg acceptors. In addition to the LVMs of Mg-H n complexes, two new modes near 2405 and 2584 cm Ϫ1 are observed from the etched p-GaN surface. We have also carried out PL and micro-Raman analyses of Mg-doped GaN films annealed under different conditions.

Low-frequency noise has been investigated for epitaxial lateral overgrown (ELO) gallium nitride (ELO-GaN). The noise parameter α evaluated was about 2. The coherent piezoelectric quantum 1/f noise theory was applied to model the experimentally obtained α and excellent correlation was achieved. The high value of α indicates the significant contribution of the piezoelectric interaction and of the transversal acoustic phonon scattering mechanism.

In this study, micro-Raman spectroscopy has been used to investigate the vibrational properties of laterally epitaxial overgrown ͑LEO͒ GaN. The LEO GaN films were grown by metal organic chemical vapor deposition on a 2 in. sapphire substrate with SiN mask. Photoluminescence and polarized Raman scattering measurements have been performed in the two regions of GaN growth ͑wing and window regions͒. Raman scattering results are consistent with the lateral growth of GaN in the overgrown region. We have observed second-order Raman scattering in the wing and window regions of GaN. The observations of longitudinal optical phonon plasmon modes in the overgrown region demonstrate that LEO GaN is doped. We have carried out micro-Raman mapping of the local strain and free carrier concentration in the LEO GaN. Anharmonicity due to temperature in LEO GaN has also been investigated. The anharmonicity was found to increase with increasing temperature, and such temperature-induced anharmonicity introduces changes in the linewidth and line center position of the Raman active phonons. The phonon lifetimes in GaN are estimated in the LEO region as well as in the coherently grown region ͑window region͒.

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