The successful growth of 2-in. -Ga 2 O 3 crystals by the edge-defined, film fed growth (EFG) method was demonstrated. The optimization of growth conditions for larger single crystalline -Ga 2 O 3 is discussed in detail. The seeding conditions of temperature and neck width were found to be the most important factors to grow single crystals. X-ray rocking curve measurements of -Ga 2 O 3 crystals were conducted to estimate the dislocation densities of the grown crystals. Etch pit densities (EPDs) of the -Ga 2 O 3 crystals were also measured using KOH solution to measure the dislocation densities. The results were discussed combining with crystal growth parameters such as neck width to clarify the mechanisms of propagation and the origin of dislocations in crystals from phenomenological and crystallographic points of view.

In this report, chemical mechanical polishing (CMP) of gallium nitride (GaN) with colloidal silica was studied. It was confirmed that colloidal silica based slurry could be used for gallium face of GaN. Removal rate of GaN was 17 nm/h under typical polishing conditions. An atomically flat surface with Ra = 0.1 nm was achieved after CMP. Detailed observation of the scratch density was done during the CMP process. Cathode luminescence (CL) imaging was used to understand the sub-surface damage induced by mechanical polishing process and its removal by CMP with colloidal silica based slurry. Combining the optical microscope, atomic force microscope (AFM), CL imaging, and reflection high energy electron diffraction (RHEED) observations before, after and at intermediate stages of the CMP process, the schematic model of the removal of scratch and damage layer from Ga-faced GaN substrate by CMP process was proposed.

The importance of the atomically well-controlled surface of sapphire substrate with slight misorientation and ideally minimized surface roughness for III–nitride epitaxy is discussed in detail. An atomically controlled surface of sapphire substrate with slight misorientation angle is modeled and an almost ideal level of atomic surface roughness of sapphire substrate is found to be obtained by a chemical mechanical polishing (CMP) with colloidal silica. Cathodoluminescence (CL) imaging indicated the complete absence of subsurface damage induced by mechanical polishing. GaN and AlN thin films are grown on misoriented sapphire substrate with an atomically controlled surface by the CMP to investigate the misorientation angle of both sapphire and grown GaN and AlN thin films. An interface model is proposed to explain the difference in misorientation angle between sapphire and III–nitride thin films, providing strong evidence of the necessity of atomically controlled surface of sapphire substrate for III–nitride epitaxy.

A systematic study to understand the relationship between wavelength uniformity and substrate curvature during InGaN growth is described in relation to the initial bow of sapphire substrate. The initial bow of the substrate acted as the offset parameter for its curvature throughout the stages of the epitaxy process. Substrate flatness during InGaN growth was found to be important for achieving high wavelength homogeneity. The impact of n-GaN layer thickness and InGaN growth temperature on the substrate curvature shape was investigated to obtain a perfectly flat substrate shape at the InGaN growth stage. Temperature adjustment showed a strong impact on substrate curvature at the InGaN growth stage. The best initial bow was found as a function of InGaN growth temperature, and the importance of the initial bow of the sapphire substrate for obtaining high homogeneity in light emitting diode (LED) wavelength was experimentally verified.

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