Preparation of AlN thin films by means of CVD using iodide source under atmospheric pressure
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1040-Q09-30
Preparation of AlN thin films by means of CVD using iodide source under atmospheric pressure Hiroki Iwane, Naoki Wakiya, Naonori Sakamoto, Takato Nakamura, and Hisao Suzuki Materials Science and Chemical Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu, 4328003, Japan
ABSTRACT Epitaxial aluminum nitride (AlN) thin films were successfully prepared on the (0001) sapphire substrate by chemical vapor deposition (CVD) using aluminum iodide (AlI3) and ammonia (NH3) under atmospheric pressure at 750 ºC. The crystallographic relationship between AlN thin films and Al2O3 substrate is in the following; AlN(0001)//Al2O3(0001) and AlN[ 1010 ]//Al2O3[ 1020 ]. Lattice parameters of AlN thin film measured by X-ray diffraction revealed that c=0.498 and a=0.311 nm, respectively. Residual stress estimated by modified sin2ψ method was 0.38 GPa in compressive stress. Cross-sectional TEM observation revealed that an interlayer lies between the AlN films and the sapphire substrate. It was suggested that relaxation of residual stress caused by the mismatching of lattice parameter and thermal expansion coefficient was brought about by the interlayer. INTRODUCTION Aluminum nitride (AlN) has been attracting attention because of its excellent physical and electrical properties such as a wide energy gap of 6.2 eV1) and a high thermal conductivity of 320 W/(m٠K)2). Therefore AlN thin film is promising for wide application such as deep ultraviolet optoelectronic devices, and high-power and high-frequency electronic devices. Recently, many researches have investigated the preparation of AlN films by chemical vapor deposition (CVD) using aluminum chloride (AlCl3)3) or metal-organic (MO) compounds4) as a starting materials. Among them, Kumagai et al. reported the success in the preparation of high quality 112 µm AlN film by the CVD using AlCl33). However, CVD processes mentioned above have following problems; CVD process using AlCl3 requires high deposition temperature more than 1200 ºC. Such a high temperature degrades a quartz glass tube reactor. MO compounds are not only expensive but also explosive and flammable as well. Therefore, the use of another source that can be reacting at lower temperature and without potential hazard of explosion should be selected. In this paper, we propose an alternative method for the preparation of the epitaxial AlN thin films, which AlI3 was used as a source of CVD. We have already reported the preparation AlN nano-pillar structure film on Si substrate using this method5)6). In this work, preparation of epitaxial AlN thin film on the sapphire substrate by this method and morphology of the films was discussed.
EXPERIMENT The AlN thin films were prepared by a CVD apparatus with a vertical hot-wall quartz reactor operating at atmospheric pressure. Sapphire substrates with c-plane polished both sides were loaded into the growth zone without any cleaning. AlN films were directly grown on the substrate without any buffer or nucleation layers. AlI3 gas reacted with NH3 in the growth zone to grow
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