Crystal growth of gallium nitride

Abstract

A review is given of the methods which have been used to grow single crystals and epitaxial layers of gallium nitride. In view of the problems in growing bulk crystals, the main emphasis is on heteroepitaxy. Sapphire has been the most popular substrate material, but leads to severe stress because of lattice and expansion mismatch. The use of an intermediate AlN layer appears to alleviate this problem. Chemical vapor deposition using gallium chloride and ammonia has given the highest quality layers to date, but a native donor remains a persistent problem. The use of high pressures of nitrogen offers promise as a means of reducing the native donor concentration. Atomic layer epitaxy is an alternative technique which looks promising for film deposition under well-controlled conditions. The properties of GaN and device considerations are included briefly in this review.