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Electrodeless photoelectrochemical (PEC) etching of GaN was studied in a K2S2O8/KOH solution irradiated with ultraviolet (UV) light either continuously or periodically. The rate of recombination of electrons and holes at dislocation defects is greater than for crystalline GaN, resulting in a rough etched surface with hexagonal pyramids. The shorter the interval of UV irradiation, the smoother is the etched GaN surface; a chopped UV source thus serves to improve the morphology of the etched surface. A uniform and smooth GaN surface was obtained with a root-mean-square roughness 0.37 nm through electrodeless PEC etching in a solution (KOH 0.01 M, K2S2O8 0.05 M) with a chopper frequency 2500 Hz (i.e., duration of irradiation 0.2 ms).

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Sputtering of the GaN(0001) surface by Ar + and N 2 + ion beams is investigated using synchrotron-radiation photoemission spectroscopy. For Ar + sputtering, the N atom is preferentially removed and a Ga-enriched GaN surface is produced. The excess Ga atoms on the Ar + -sputtered surface aggregate to form metallic Ga clusters at temperatures above 623 K. A better-ordered GaN(0001)-1 × 1 surface can be obtained by N 2 + sputtering, instead of Ar + sputtering. In addition to acting as a sputtering particle, the N 2 + ion also serves as a reactant which compensates for the preferential loss of the N atom caused by physical ion bombardment. During chlorination of GaN, chlorine preferentially reacts with surface Ga atoms to form Ga chlorides. Although Ga monochloride (GaCl) is the major product formed on the N 2 + -sputtered surface, however, volatile chlorides (GaCl 2 and GaCl 3 ) are mainly produced on the Ar + -sputtered surface. The formation of volatile products on the Ar + -sputtered GaN surface may result in higher etching rates and lower etching temperatures for ionassisted chemical etching.

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White electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device. Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1. Measured x value of the film is 0.56, and the corresponding photoluminescence of a-SiN0.56:H thin film exhibited a red-infrared spectrum, centered at 630 nm. The layer structure of the EL device is ITO/a-SiN0.56:H (80 nm)/Al, with light emitting from the ITO layer, recognizable by the naked eye in the dark, under the 14 V forward bias conditions. White EL spectra from ∼400 to 750 nm, with a central peak at 560 nm, were observed in the hydrogenated amorphous silicon nitride EL device. A carrier transport mechanism was suggested, and the EL was attributed to the recombination of carriers through the luminescent states.

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