Selective growth of GaN on sapphire substrates treated with focused femtosecond laser pulses Hisashi Matsumura a,Ã , Shunro Fuke b , Takayuki Tamaki c , Yasuyuki Ozeki c , Kazuyoshi Itoh c , Yasuo Kanematsu a a Venture Business Laboratory, Center for Advanced Science and Innovation, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan b Department of Electrical and Electronic Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan c Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan article info Article history: Received 7 January 2008 Received in revised form 16 September 2008 Accepted 17 September 2008 Communicated by M.S. Goorsky Available online 7 October 2008 PACS: 81.15.Gh 81.65.Cf 85.40.Hp Keywords: A1. Substrate A1. Surface processes A3. Metalorganic chemical vapor deposition B1. Nitrides abstract We developed a novel selective growth technique for metalorganic chemical vapor deposition (MOCVD) growth of GaN using an unique substrate treatment procedure; sapphire substrates were treated and patterned with focused femtosecond laser pulses. By adjusting laser-irradiation conditions, GaN film growth could be suppressed over the laser-irradiated region. Using organic layer deposition onto a sapphire substrate prior to laser irradiation, we could achieve selective growth of GaN without sapphire ablation. Compared with the conventional technique, the present selective growth procedure is characterized by patterning without the need for the etching process or mask layers. & 2008 Elsevier B.V. All rights reserved. 1. Introduction Selective growth using metalorganic chemical vapor deposi- tion (MOCVD) can be applied for forming two-dimensional microstructures without the need for the etching process [1]. Especially, for GaN-based materials, this technique has been employed to form microstructures such as periodic patterns [2], ridge waveguides [3], cavity mirrors [4], and photonic crystal structures [5]. Furthermore, this technique has been employed to reduce threading dislocation density during growth [6–8] with the idea of controlling side facets during lateral overgrowth [9,10], and it has been applied for fabricating laser diodes [11]. By fabricating periodical microstructures, application of GaN in nonlinear optical material is anticipated, since phase mismatch arising from GaN dispersion would be compensated (quasi-phase matching). Such periodical microstructures, for example GaN-air photonic crystals, have been previously fabricated, and nonlinear optical processes such as second-harmonic generation (SHG) [12] has been carried out. Especially, difference frequency generation (DFG) would be useful for realizing a robust and bright mid-infrared light source (l45 mm; ‘‘fingerprint region’’), since GaN is characterized by its chemical stability, thermal stability, wide transparency window (0.365–13 mm) [13], and the operation at room temperature. Conventionally, selective growth of GaN has been achieved by either (1) using growth masks on a GaN film [6,8,14] or (2) forming trenches on a substrate surface [15]. However, those methods require complex procedures including lithography and etching processes during patterning mask layers, and such etching processes sometimes result in ion-induced damages and high density of surface states [16]. Furthermore, since the mask layers must be embedded within a GaN layer, such foreign layers would cause refractive index modulation, and would degrade the quality for the application of GaN to nonlinear optical material. To solve these problems, we have previously investigated substrate treatment procedures; the sapphire substrate surface was treated and patterned with an electron beam prior to MOCVD growth of GaN [17]. Over the surface areas exposed to electron beam, GaN hardly grows, resulting in groove-like structures with dimensions ranging from micrometer to sub- micrometers. Surface damages would be avoided by patterning prior to GaN growth. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2008.09.165 Ã Corresponding author. Tel.: +816 6879 7755; fax: +816 6879 7878. E-mail address: matsumura@casi.osaka-u.ac.jp (H. Matsumura). Journal of Crystal Growth 310 (2008) 5278–5281