| Abstract Scope |
InN has potentialities for optical device applications because of its narrow bandgap of 0.6-0.8 eV. However, there is a difficulty in obtaining a high crystalline quality InN due to the low dissociation temperature and lack of lattice-matched substrates. In general, sapphire is used as a substrate for the growth of InN. So far various buffer layer techniques and an increased film thickness up to 10 μm have been employed, which were valid to some extent, but inefficient in decreasing the dislocation density below 10<SUP>9</SUP> cm<SUP>-2</SUP>. Meanwhile, selective-area growth (SAG) provided epitaxial lateral overgrowth (ELO); it is a dramatically-effective method for reduction of threading dislocation of GaN, as well developed with HVPE and MOVPE. Contrarily, SAG of InN has not been well developed yet. The SAG by MOVPE of InN was tried on GaN template using SiO2 masks, following the conventional SAG of GaN. For preventing crystal deposition on SiO2 masks, a high temperature growth was necessary, but which induced decomposition of InN. Recently, by use of Molybdenum mask, Denker et al. reported SAG of InN at low temperature by rf-MBE. In this study, the SAG of InN was beautifully obtained, by which the first achievement of ELO in InN crystals was demonstrated. Prior to the growth, a thin Mo film was deposited on c-plane sapphire substrate by electron beam evaporation. Subsequently we prepared Mo-mask patterns through electron beam lithography and dry etching, in which hexagonally shaped holes with diameter of 433 nm were arranged in triangular lattice of lattice constant of 1000 nm. After initial nitridation of the substrate surface at 550°C, InN was grown at 510-580°C for 1-60 min. by rf-MBE, producing InN micro-crystals. The grown InN micro-crystals were evaluated with SEM, TEM and micro-PL spectroscopy. The growth of the InN micro-crystals proceeded as follows; the nucleation occurred firstly inside the holes opened in the Mo-mask and then hexagonal nano-disks were formed at 5 min. and then InN grew laterally and vertically. At 60 min., hexagonal geometry columnar InN micro-crystal arrays in closed packing scheme were prepared. The height and diameter were approximately 1.5 μm and 1.0 μm, respectively. TEM observation confirmed that a large number of threading dislocations (10<SUP>9</SUP>-10<SUP>10</SUP> cm<SUP>-2</SUP>) arose at InN/sapphire interface and propagated in the center area of the InN micro-crystals along the crystal c-axis, while laterally overgrown side areas were nearly dislocation-free. The micro-PL spectrum at room temperature showed the PL-FWHM of 54 meV at the peak energy of 0.63eV, indicating a high quality of the InN. Acknowledgment: This study was partly supported by Grants-in-Aid for Scientific Research on Priority Areas No.18069010, and (B) No.18310079 from the MEXT, Japan. |