Heteroepitaxial growth of ZnO films on Gd 3 Ga 5 O 12 garnet substrates
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Heteroepitaxial growth of ZnO films on Gd3Ga5O12 garnet substrates Yosuke Ono1, Hiroaki Matsui1,2, and Hitoshi Tabata1,2 1 Department of Electrical Engineering and Information Systems, the University of Tokyo, Tokyo 1130032, Japan 2 Department of Bioengineering, the University of Tokyo, Tokyo 113-0032 ABSTRACT This study focused on structural and optical properties of ZnO films grown epitaxially on Gd3Ga5O12 substrates. ZnO films (a = 3.2439 Å and c = 5.2036 Å) were deposited on the (001) and (111) planes of Gd3Ga5O12 (GGG: a = 12.383 Å) garnet substrates by a pulsed laser deposition method. From out-ofplane and in-plane X-ray diffraction measurements, the obtained ZnO films showed a single phase with the (0001) orientation on the GGG (001) and (111) substrates. The epitaxial relations between the ZnO film and GGG (001) substrate were [10-10] ZnO || [100] GGG and [10-10] ZnO || [010] GGG, while the epitaxial relations between the ZnO film and GGG (111) substrate were [10-10] ZnO || [11-2] GGG ±21°. Furthermore, transmittance electron microscopy revealed sharp interfaces between ZnO films and GGG substrates. From photoluminescent spectra, the ZnO films showed donor bound emissions superimposed with free excitons at a low temperature of 10 K. INTRODUCTION Rare earth (RE) garnets, Re3Fe5O12, have received much attention because of their magnetism and magneto-optical properties. These properties are expected to be promising for practical applications such as scintillations [1], microwave magnets [2], and optical isolators [3]. Epitaxial layer growth of garnets is usually performed using garnet-types of substrate in order to obtain high quality garnet films. However, Re3Fe5O12 single crystals with micrometer sizes are markedly limited for device applications because it is not easy to use garnet crystals with micrometer sizes. Unfortunately, it has not been achieved epitaxial layer growth of garnet materials on non-garnet substrates. To date, heteroepitaxy on garnet substrates has been only reported using compound semiconductors such as InP [4] and GaAs [5]. In this work, we found that ZnO grew epitaxially on the GGG (001) and (111) substrates. In order to achieve epitaxial layer growth of garnet materials on non-garnet substrates, it is indispensable for understanding epitaxial layer growth of non-garnet materials on garnet substrates as a first step. In this paper, we report the higher ordered epitaxial growth of ZnO on Gd3Ga5O12 (GGG) substrates. This growth technique is applied for ZnO epitaxial layers on c-face Al2O3 substrates [6]. We believe that this study contributes to elucidate origin of heteroepitaxial growth of non-garnet materials on garnet substrates. EXPERIMENT Prior to film growth, GGG (001) and (111) substrates were annealed at a high temperature of 1250 oC for 2.5 hours. ZnO films were grown on the GGG substrates at 800 oC by pulsed laser ablation. ArF excimer laser pulses (193 nm, 3Hz and 4 J/cm 2) were focused on ZnO ceramic targets (5N) away 5 cm from the substrates in oxygen ambient of 1.8 x 10-1 Pa
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