Effects of the Nitridation Process of (0001) Sapphire on Crystalline Quality of InN Grown by RF-MBE
- PDF / 137,529 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 77 Downloads / 204 Views
E4.2.1
Effects of the Nitridation Process of (0001) Sapphire on Crystalline Quality of InN Grown by RF-MBE Daisuke Muto1, Ryotaro Yoneda1, Hiroyuki Naoi2, Masahito Kurouchi1, Tsutomu Araki1 and Yasushi Nanishi1 1 Dept. of Photonics, Ritsumeikan Univ., 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan 2 Center for Promotion of the COE Program, Ritsumeikan Univ., 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan ABSTRACT The effects of the nitridation process of (0001) sapphire on crystalline quality of InN were clearly demonstrated. The InN films were grown on NFM (nitrogen flux modulation) HT-InN or LT-InN buffer layers, which had been deposited on nitridated sapphire substrates. We found that low-temperature nitridation of sapphire is effective in improving the tilt distribution of InN films. Whereas the twist distribution remained narrow and almost constant, independent of nitridation conditions, when LT-InN buffer layers were used. The XRC-FWHM value of 54 arcsec for (0002) InN, the lowest reported to date, was achieved by using the LT-InN buffer layer and sapphire nitridation at 300○C for 3 hours.
INTRODUCTION InN is one of the most promising materials for high-speed electronic devices and long-wavelength opto-electronic devices since it has the highest peak and saturation velocities and smallest direct bandgap among the group III nitride semiconductors. Of special note is its bandgap energy recently reported to be 0.6-0.7 eV [1-3] rather than the previously accepted value of 1.9 eV [4, 5]. This finding has expanded the application fields of InN and its alloys into longer-wavelength devices, such as laser diodes for optical communication and high-efficiency solar cells. However, it is still difficult to obtain high-quality InN films. One reason is the lack of suitable substrate materials that are lattice matched to and thermally compatible with InN. Thus, a variety of substrates have been studied in an attempt to obtain high-quality InN [6]. Epitaxial growth of InN generally employs (0001) sapphire as substrate because of its low cost and high thermal stability, and experimental data suggesting that relatively high-quality InN can easily be grown on it. Nitridation of sapphire substrates prior to growth improves the crystalline quality of InN [7-10] because i) the formation of AlN on the sapphire surface reduces the in-plane lattice mismatch between InN and the underlying layer from ~25% for [11-20]InN || [11-20]sapphire to nominally ~13% for [10-10]InN || [10-10]AlN [7] and ii) AlN formation, thought to occur through the 30° rotation of the in-plane epitaxial relationship with sapphire, suppresses the generation of
E4.2.2
a multi-domain InN structure. This multi-domain structure InN is generally considered to be formed because of the similar in-plane lattice-mismatch values of ~25% for [11-20]InN || [11-20]sapphire and ~29% for [10-10]InN || [11-20]sapphire. The above epitaxial mechanism induced by the formation of AlN successfully explains the in-plane orientation relationship of [10-10]InN || [10-10]Al
Data Loading...
