Journal of Crystal Growth 237–239 (2002) 2112–2115 Influence of pressure control on the growth of bulk GaN single crystal using a Na flux M. Onda*, T. Iwahashi, M. Okamoto, Y.K. Yap, M. Yoshimura, Y. Mori, T. Sasaki Department of Electrical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565 0871, Japan Abstract We investigated the influence of N 2 pressure control on the growth of bulk GaN crystals by using a Na flux. GaN single crystals with a maximum dimension of 3mm could be obtained by this method, though smaller crystals of 0.5–2mm in size have been grown without pressure control. This suggested significant effects of additional NH 3 gas on growth of GaN crystals in the Na flux method. r 2002 Published by Elsevier Science B.V. PACS: 81.10; 81.10; 42.55.P Keywords: A1. Single crystal growth; A2. Growth from melt; B1. Nitrides; B2. Semiconducting III–V materials; B3. Laser diodes; B3. Light emitting diodes 1. Introduction Recently, bulk GaN single crystals have received much interest due to the need of GaN substrates for homoepitaxial growth of GaN in order to realize advanced blue-light emitting diodes and lasers [1]. However, the growth of GaN single crystals from solution requires temperatures as high as 16001C and N 2 gas pressures as high as 10,000 atms [2]. In 1997, Yamane et al. reported that high-quality bulk GaN single crystals can be obtained at a relatively low temperature and pressure of 8001C and 100 atm by using the Na flux method [3,4]. However, this method has some problems. First, the nucleation site and the number of GaN single crystals nucleated are still not controlled, so it is still difficult to obtain large GaN single crystals with high reproductivity [5,6]. Second, the growth rate of GaN crystals is inadequate because of the low N 2 dissolution in Ga melt. In order to obtain large GaN single crystals, it is necessary to control the nucleation of GaN and enhance the dissolution of nitrogen in the Ga melt [7]. The main parameters for growth of GaN crystals in the Na flux method are temperature and pressure. Therefore, changing the pressure seems to change the supersaturation in this growth system, reducing nucleation sites. Ammonia gas (NH 3 ) is superior to N 2 gas with respect to reactivity to molten Ga. N 2 gas does not react with Ga metal under low pressure, but NH 3 gas does. *Corresponding author. Tel.: +81-6-6879-7707; fax: +81-6- 6879-7708. E-mail address: onda@ssk.pwr.eng.osaka-u.ac.jp (M. Onda). 0022-0248/02/$-see front matter r 2002 Published by Elsevier Science B.V. PII:S0022-0248(01)02269-2