Kazumasa Hiramatsu

Hydrogen and Nitrogen Ambient Effects on Epitaxial Lateral Overgrowth (ELO) of GaN Via Metalorganic Vapor-Phase Epitaxy (MOVPE)

Ambient gas effect on the epitaxial lateral overgrowth (ELO) of GaN via metalorganic vapor-phase epitaxy (MOVPE) on a MOVPE-grown GaN (0001) / sapphire (0001) substrate with a SiO 2 stripe mask has been studied by means of field-emission scanning electron microscopy (SEM) and high-resolution X-ray diffraction (XRD) analysis. Different ambient gases of nitrogen, hydrogen and their mixture (mixture ratio, hydrogen: nitrogen = 1: 1) affect the lateral overgrowth rate, the surface morphology and the crystalline tilting of ELO-GaN layers. XRD revealed that the ELO-GaN layer on the SiO 2 mask aligned along the 1 00> direction exhibited anisotropic crystalline tilting toward 2 0>. For ELO-GaN growth in nitrogen ambient, the growth rate of the (0001) facet decreases, the lateral overgrowth rate increases and the tilting of the ELO-GaN layer increases, while no smooth surface is obtained, in comparison with ELO-GaN growth in hydrogen ambient. For the mixture ambient, a smooth surface with a fast lateral overgrowth rate is achieved and the dislocation density is not more than 10 7 cm -2 , which is comparable to that in hydrogen ambient.

High-temperature annealing of AlN on sapphire using face-to-face method (Conference Presentation)

To fabricate such deep UV devices, a high-quality underlying AlN film is desirable because of its wide bandgap. In this work, we studied the effects of thermally annealing sputtered AlN films grown on sapphire substrates on the crystallinity and surface morphology, where the thermal annealing was performed in nitrogen ambient. The effects of annealing were investigated as a function of the sputtered AlN film thickness and the thermal annealing temperature. The thicknesses of the sputtered AlN films were 170 and 340 nm. Subsequently, the sputtered AlN films were thermally annealed in N2 at 1600 - 1700 oC for 1 h. Both the (0002) and (10-12) XRCs of the AlN films had a single sharp peak after thermal annealing owing to the elimination of the tilt and twist components from the sputtered AlN films by high-temperature thermal annealing. The improved crystallinity is related to the solid-phase reactions that occur at high annealing temperatures. The FWHMs of the (0002) and (10-12) XRCs were markedly reduced from 532 to 49 and 6031 to 287 arcsec, respectively. Cross-sectional STEM images of sputtered AlN on sapphire substrate after annealing were observed. Columnar structures are observed in grown layer before annealing while they disappear after annealing. With annealing, hexagonal shaped voids pointed by white arrows form and the polarity invert from N-polar to Al-polar about 10 nm away from AlN/sapphire interface.