Journal of Crystal Growth 237–239 (2002) 993–997 Effect of sapphire substrate nitridation on determining rotation domain in GaN growth T. Yamaguchi a, *, T. Araki a , Y. Saito a , K. Kano a , H. Kanazawa a , Y. Nanishi a , N. Teraguchi b , A. Suzuki b a Department of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan b Advanced Technical Research Labs., Sharp Corp. 2613-1 Ichinomoto, Tenri, Nara 632-8567, Japan Abstract GaN films were grown at various V/III ratios on sapphire (0 0 0 1) substrates with and without nitridation process by radio-frequency plasma-excited molecular beam epitaxy. Based on the results of X-ray diffraction pole-figure and f scan measurements, the GaN film grown without nitridation process has a tendency to form the metastable in-plane rotation domain by B111 from the substrate, in addition to the main domain rotated by 301 from the substrate. In suppressing the formation of the metastable in-plane rotation domain, it is found to be very effective to perform the nitridation process. In addition, even in GaN films grown without nitridation process, decrease in V/III ratio enables us to suppress the formation of the metastable domain. The rotation domains are considered to have the epitaxial relationship of ½12 % 30 GaN 8½11 % 20 sapphire and ½ % 1 % 230 GaN 8½11 % 20 sapphire : r 2002 Elsevier Science B.V. All rights reserved. PACS: 61.10.Kw Keywords: A1. Substrates; A1. X-ray diffraction; A2. Single crystal growth; A3. Molecular beam epitaxy; B1. Nitrides 1. Introduction GaN and related III–V nitride semiconductors have been promising materials for optoelectronic devices in the visible and ultraviolet regions, and electronic devices that can be operated at high- temperature, high-frequency and high-power con- ditions. Until now, there has been a remarkable progress in GaN growth techniques, and nitrida- tion process of sapphire substrate is well known as one of the key processes in order to obtain better quality GaN films by molecular beam epitaxy (MBE) [1]. It is reported that nitridation process improves the structural, morphological and optical properties of GaN films [1,2]. Moreover, it is reported that GaN films grown without nitridation process exhibit a different crystallographic orientation of ½10 % 10 GaN 8½11 % 20 sapphire and ½10 % 13 GaN 8½11 % 20 sapphire which corresponds to a tilt of the c-axis with respect to the substrate surface, while GaN films grown with nitridation process have only ½10 % 10 GaN 8½11 % 20 sapphire [3,4]. It is considered that the formation of AlN-relaxed *Corresponding author. Tel.: +81-77-561-2884; fax: +81- 77-561-3994. E-mail address: ro012961@se.ritsumei.ac.jp (T. Yamaguchi). 0022-0248/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)02114-5