The effects of Na and some additives on nitrogen dissolution in the Ga-Na system: A growth mechanism of GaN in the Na flux method

In the growth of GaN single crystal using the Na flux method, we succeeded in clarifying the role of Na in promoting nitrogen dissolution in the Ga-Na melt system above 900 K. At the gas-liquid interface of high temperature Ga-Na melt, Na functions to ionize the nitrogen gas. The ionization of the nitrogen gas results in drastic increase of nitrogen dissolution in the melt. In consequence, these synthesize GaN single crystals easily. On the other hand, the addition of a minor amount of Ca or Li to the Ga-Na melt system also increases the nitrogen dissolution. However, the additives function to maintain the nitrogen dissolved in the Ga-Na melt, which results in drastic increase in the nitrogen concentration. In the present study, we report the solubility of GaN in the Ga-Na system and the threshold pressure of nitrogen gas to grow GaN. On the basis of these data, we propose a growth mechanism of GaN and the role of additives to maintain nitrogen. (C) 2005 Springer Science + Business Media, Inc.