Effects of Growth Temperature on Morphology of GaN Crystals by Na Flux Liquid Phase Epitaxial Method

The morphology of GaN crystals grown in a temperature range of 800–860°C by the Na flux liquid phase epitaxial (LPE) method was observed by the optical microscope and the scanning electron microscope (SEM). Significant changes in the morphology of as-grown GaN crystals occurred with the growth temperature being increased. Differing from the crystals grown at the temperature lower than 840°C, the side morphology of crystals grown at 850°C and 860°C presented a rather integrated and flat facet observed along the m -direction. In addition, there were two distinct growth stages with lateral equilibrium epitaxial growth (Stage I) and c direction growth (Stage II) during the epitaxial growth process. Under the growth temperature of 850°C and keeping nitrogen pressure 3 MPa for 150 h, the as-grown GaN crystal had relatively higher crystalline quality, the thickness and yield of GaN-LPE crystal were about 622 μm and 15.2%, respectively. The dislocation density in the GaN crystal was also remarkably reduced to the order of 10 5 –10 6 cm −2 . Therefore, the continuous lateral equilibrium epitaxial growth (stage I) is feasible to achieve a large size and high quality GaN single crystal.