Electrical Properties of InN Grown by RF-MBE
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Electrical Properties of InN Grown by RF-MBE Yoshiki Saito, *Nobuaki Teraguchi, *Akira Suzuki, Tomohiro Yamaguchi, Tsutomu Araki and Yasushi Nanishi Department of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu 525-8577, Japan. * Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto, Tenri, Nara 632-8567, Japan. ABSTRACT InN films with excellent surface morphology were grown by controlled the V/III ratio of InN epitaxal layer. It was found they were single crystal of InN films with wurtzite structure by X-ray diffraction (XRD) measurement and reflection high-energy electron diffraction (RHEED) observation. Hall mobility as high as 760 cm2/Vs was achieved for InN film grown at 550°C with 240 W of RF plasma power with a carrier density of 3.0× ×1019 cm-3 at room temperature. To our knowledge, this electron mobility is the highest value ever reported.
INTRODUCTION Of the group III-V nitride semiconductors, InN has the smallest effective mass of 0.11 mo at 1 valley [1] and the highest electron drift velocity of 4.2× ×107 cm/s [2]. These attractive physical properties indicate that this material has a possibility for high speed and high frequency electronic devices. On the other hands, as InN has the smallest band gap energy of 1.9 eV at room temperature [3], this material is expected for optoelectronic devices. It is also used as an interface layer for ohmic contacts [4]. However, the growth of high quality InN is very difficult because of some reasons. One is that InN has an extremely high dissociation pressure [5]. Another reason is the lack of suitable substrate materials that are matched both in lattice constant and thermal expansion coefficient with InN. Therefore, InN films with excellent electrical properties have not been obtained for a long time. For example, reported values of electrical properties have been electron mobility of 1020 cm-3 [6]. Recently, Yamaguchi et al., has reported [7] InN films with electron mobility of 700 cm2/Vs and carrier density of 5× ×1019 cm-3 grown by metalorganic vapor phase epitaxy (MOVPE) technique on a GaN/sapphire. Lu et al., has also ×1018 cm-3 grown by migration enhanced reported [8] InN films with electron mobility of 540 cm2/Vs and carrier density of 3× epitaxy (MEE) technique on sapphire. In this study, we report on the relation between growth conditions and electrical properties. The crystallinity and film structure of InN are also reported.
EXPERIMENTAL InN films were grown by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). The elemental indium (In) was evaporated from a standard Knudsen effusion cell, and RF plasma source (SVT associates model 4.5) with mass-flow controlled N2 gas was used to obtain excited nitrogen. The substrate used in this study was (0001) sapphire. Figure 1 shows the growth time chart of InN films. The substrate was cleaned by organic solvent and loaded into vacuum. Prior to growth, the sapphire substrate was thermally cleaned. The background pressure of the growth chamber was around 1× ×10
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