Aluminum Nitride Crystal Growth by Halide Vapor Transport Epitaxy
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Aluminum Nitride Crystal Growth by Halide Vapor Transport Epitaxy 2 1 1 2 2 V. L. Tassev , D. F. Bliss , D. Weyburne , J. S. Bailey , S.-Q. Wang 1
Air Force Research Laboratory, Sensors Directorate, 80 Scott Road, Hanscom AFB MA 01731 Tel: (781) 377-4247; Fax: (781) 377-3717; E-mail: [email protected] 2 Solid State Scientific Corporation, Hollis, NH 03049
Abstract Halide vapor transport epitaxy (HVTE) is demonstrated for growth of AlN layers with thickness up to 50 µm at deposition rates up to 60 µm/h. The HVTE process uses an aluminum chloride amine adduct as the aluminum source of both aluminum and nitrogen. This new technique eliminates the main difficulties of the conventional hydride VPE growth, where aluminum oxidation and the strong reactivity of aluminum chloride with fused silica create the potential for oxygen contamination. This study shows the effect of temperature, gas flow velocities, and reactor pressure on the growth rate and layer quality. It is found that the growth rate and the layer quality strongly depend on the gas ratio. The species of carrier gas, the flow rates and partial pressures can be used as tools to optimize growth rate and to avoid any etching effects resulting from reverse chemical reactions. The crystalline layer quality as determined by x-ray rocking curve measurement shows FWHM of 300-900 and 500-1300 arc-sec for (002) and (102) planes, respectively. PACS: 81.05.Ea; 81.15.Kk; 68.55.Jk. Keywords: A3.Halide vapor phase epitaxy; B1.Nitrides.
1. Introduction Thick-film aluminum nitride on sapphire can be used as a substrate material for a wide range of optical and electronic applications from UV sensors to high power RF devices. The properties that make it attractive are its high thermal and low (insulating) electrical conductivity [1], high UV transparency [2], high acoustic wave velocity [3], and its excellent lattice and thermal expansion match with GaN [4]. The choice of a VPE process for growth of aluminum nitride layers is dictated by the possibility of high growth rates compared with other methods, including reactive sputtering [6], MBE [7], MOCVD [8] and VPE [9]. Only VPE has a high growth rate for well-oriented AlN film growth. This paper covers the most recent results of AlN film growth by the HVTE process. Our approach uses a pre-synthesized aluminum chloride adduct as the source material. Several authors have discussed adduct preparation [11,12] and the adduct properties [13,14,15]. The use of the aluminum chloride amine adduct circumvents the high affinity of pure aluminum for oxygen and the strong reactivity of aluminum chloride to the quartz reactor walls. At the same time, the adduct contains within itself both sources – of aluminum and nitrogen. Thus, the deposition can be easily controlled by the temperature and gas flow rate. In what follows, we present the results of AlN film growth by the HVTE process using the preformed adduct.
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2. Experimental The halide vapor transport epitaxy (HVTE) system for III-nitride layer growth is des
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