Two Step Growth of InN Films on Sapphire (0001) Substrates Without Nitridation Process by RF-MBE
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Two Step Growth of InN Films on Sapphire (0001) Substrates Without Nitridation Process by RF-MBE
Tomohiro Yamaguchi, Yoshiki Saito, Kenji Kano, Tomo Muramatsu, Tsutomu Araki and Yasushi Nanishi Dept. of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu 525-8577, JAPAN. Nobuaki Teraguchi and Akira Suzuki Advanced Tech. Res. Labs., Sharp Corp., 2613-1 Ichinomoto, Tenri 632-8567, JAPAN.
ABSTRACT InN films were grown on sapphire (0001) substrates by radio-frequency plasma-assisted molecular beam epitaxy. The InN buffer layers deposited at low temperature were either grown on a substrate with nitridation or on a substrate without nitridation. The InN buffer layers on the nitridated substrates were always single crystalline, whereas the buffer layers on non-nitridated substrates were always polycrystalline. However, even without nitridation process, single crystalline InN films could be grown on the polycrystalline InN buffer layers; in this case, the orientation was always [ 1120 ] InN//[ 1120 ] sapphire epitaxy, which differed from the [ 10 1 0 ] InN//[ 1120 ] sapphire epitaxy in films grown with nitridation.
INTRODUCTION Group III nitride semiconductors, such as GaN, AlN, InN, and their combinations, are promising materials for optoelectronic devices with light ranging from the ultraviolet to the visible. Furthermore, extensive research has been done to apply these materials to electronic devices. However, nitrides have few suitable substrates due to their large lattice mismatch, which means that the right initial growth process is needed to solve this problem. Nitridation of a sapphire substrate is one such initial process that has been studied. In the growth of GaN, which is a pioneer among nitrides, nitridation prior to growth has been found to improve the quality of epitaxial films.[1-4] However, such studies have reported different results including different nitridation times, different temperatures, and different layer properties on the substrate surface. In spite of these differences, nitridation might also be necessary for the InN growth[59]; for example, high electron mobility InN films grown with nitridation have been reported [8,9]. InN films grown without nitridation tend to become polycrystalline. In the direct growth without nitridation, there is a tendency to have a multidomain structure within the c-plane by having various a-axis orientations.[10] Tsuchiya et al. used spinel instead of sapphire as a substrate to solve this problem.[11] This problem also appeared in the growth of ZnO on sapphire (0001) substrate; Fons et al. used sapphire ( 1120 ) instead of sapphire (0001) as a substrate to solve the problem.[12] Recently, we could suppress the rotation domains of InN films grown directly on sapphire (0001) substrates[13]; however, the method was very sensitive to the growth conditions. I3.41.1
In this paper, we report that single crystalline InN films could be always grown on low temperature InN buffer layers even without nitridation process. The orientation was always [ 1120 ] InN//
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