Search for content and authors
 

Atomically-flat ScAlMgO4 single-crystalline films fabricated by reactive solid-phase epitaxy; Effects on growth of ZnO and GaN

Takayoshi Katase 1Kenji Nomura 2Hiromichi Ohta 2,3Hiroshi Yanagi 1Toshio Kamiya 1,2Masahiro Hirano 2,4Hideo Hosono 1,2,4

1. Materials and Structures Laboratory, Tokyo Institute of Technology (TOKYOTECH), R3-1, 4259 Nagatsuta, Midori-ku, Yokohama, JAPAN, Kanagawa 226-8503, Japan
2. ERATO-SORST, Japan Science and Technology Agency, in Tokyo Institute of Technology, Mailbox S2-13, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
3. Garaduate School of Enginnering, Nagoya University (NAGOYAU), Nagoya university, Furo-cyo, Chikusa-ku, Nagoya 464-8603, Japan
4. Frontier Reserch Center, Tokyo Institute of Technology (FRC), R3-1, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503, Japan

Abstract

ZnO and GaN have been investigated for optoelectronic devices including UV-LEDs and TFTs. However, they are, in general, grown on c-sapphire or YSZ single crystal substrates but these have large lattice mismatchings with ZnO and GaN (Da/a > 10 %), which leads to a three-dimensional spiral grain growth and high-density defects. Therefore a lattice matched substrate or buffer layer is important to reduce the defects and to improve carrier transport properties [1]. Homologous series compounds such as ScAlMgO4 (SCAM) with the chemical formula of RMO3(AO)3 have good lattice matching with ZnO and GaN (Da/a ~ 0.1 %).

Here we report the fabrication of single-crystalline thin films of SCAM on (111)-oriented YSZ single crystals by PLD and their application to buffer layers for ZnO and GaN. The SCAM films were fabricated by reactive-solid phase epitaxy (R-SPE) using bilayer composed of amorphous-SCAM / thin epitaxial ZnO template (~10 nm) [2].

In preliminarily experiments, it was found that 20mol% excess addition of Sc2O3 was necessary to obtain pure SCAM films. To obtain atomically-flat SCAM films, 40% Zn was added with respect to Mg in the PLD target. Finally, step-and-terraced epitaxial films were obtained with the relationships of [000l]SCAM // [111]YSZ in out-of-plane and [11-20]SCAM // [1-10]YSZ in in-plane. The SCAM layers were applied to buffer layers for growing ZnO and GaN films. The SCAM buffer layer enhanced the lateral growth of the ZnO layer to > 1 micrometer and resulted in step and flow growth at 800 oC. For GaN films grown by N2 source RF-MBE on the SCAM, residual carrier concentration was reduced to ~ 4.0×1017 cm-3 and Hall mobility was increased to ~140 cm2/Vs compared to ~2.0×1018 cm-3 and ~120 cm2/Vs for GaN on Al2O3 (0001) a low temperature GaN buffer layer.

[1] A. Ohtomo et al., Appl. Phys. Lett. 75, 17 (1999).  [2] H. Ohta et al., Adv. Funct. Mater.13, 2 (2003).

 

Legal notice
  • Legal notice:
 

Related papers

Presentation: Oral at E-MRS Fall Meeting 2008, Symposium B, by Takayoshi Katase
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-16 00:11
Revised:   2009-06-07 00:48