A Feasibility Study on the Growth of Bulk GaN Single Crystals.

In the previous report, a breakthrough was reported in attempts to prepare large crystals of GaN, in that the maximum crystal size had been increased for the first time above 1 mm. The emphasis in the previous quarter has been to obtain an improved understanding of the factors leading to this improvement and so to determine the conditions necessary for the next advance. Experimental work has been concentrated on the horizontal crucible method which has shown the greatest promise to data. In order to study in more detail the reaction between ammonia and liquid gallium, a series of experiments has been performed in which ten samples were located in separate recesses in a compartmented quartz cruicible. The overall length of the crucible was 15 cm, as in the case of a single vitreous carbon boat, and the compartmented tube was located in the same temperature gradient as in previous experiments with the carbon boat 1010-825 C. The ratio of ammonia to hydrogen flows was 0.002, as in the experiments of Logan and Thrumond, and the hydrogen flow rate was about 225 cu cmmin. The reaction proceeded for 12 days in each case. Prior to crystal growth, the furnace was purged with hydrogen for 12 hours at room temperature, followed by 24 hours at about 1200 C.