Properties of Nanocrystalline 3C-SiC:H and SiC:Ge:H Films Deposited at Low Substrate Temperatures
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0910-A04-01
Properties of Nanocrystalline 3C-SiC:H and SiC:Ge:H Films Deposited at Low Substrate Temperatures Shinsuke Miyajima1, Akira Yamada2, and Makoto Konagai1 1 Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1-S9-9 O-okayama, Meguro-ku, Tokyo, 152-8552, Japan 2 Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-S9-9 Ookayama, Meguro-ku, Tokyo, 152-8552, Japan
ABSTRACT We have investigated properties of nanocrystalline hydrogenated cubic silicon carbide (nc-3C-SiC:H) and silicon carbide: germanium alloy (nc-SiC:Ge:H) films deposited by hot-wire chemical vapor deposition (HWCVD) at low temperatures of about 300oC. we found that the density of charged defects was strongly influenced by grain size of the films. In-situ doping into nc-3C-SiC:H films was also carried out. N-type nc-3C-SiC:H films were successfully deposited by using phosphine (PH3) and hexamethyldisilazane (HMDS) as dopants. We found that HMDS is an effective n-type dopant for low temperature deposition of nc-3C-SiC:H films by HWCVD. For the deposition of p-type nc-3C-SiC:H with trimethylaluminum (TMA), it was found that the substrate temperature of above 300oC is required to activate the acceptors. We added dimethylgermane (DMG) into mixture of MMS and H2 to prepare nc-SiC:Ge:H films. The ncSiC:Ge:H films with Ge mole fraction of 1.9% were successfully deposited. INTRODUCTION Crystalline cubic silicon carbide (c-3C-SiC) is one of the well known wide band gap materials. This material is suitable for the window layer of thin film silicon based solar cells and heterojunction crystalline silicon solar cells since the absorption coefficients of c-3C-SiC in visible light region are quite low due to its wide band gap of 2.2-2.4 eV and its indirect band structure [1,2]. Low-temperature deposition of c-3C-SiC is required for the application described above, however growth of c-3C-SiC requires high substrate temperatures of about 1000oC [3] in general. The solution of this problem is nanocrystalline hydrogenated cubic silicon carbide (nc3C-SiC:H). Several reports on the deposition of undoped nc-3C-SiC:H at a substrate temperature of about 300oC are available now [4-8]. Doping into nc-3C-SiC:H is indispensable to apply a nc3C-SiC:H film to a window layer of the solar cells. However, there a few reports on the deposition of p-type and n-type nc-3C-SiC:H at low substrate temperatures [9-11]. Germanium addition into nc-3C-SiC:H is a potential technique to control the band gap of group IV nanocrystalline materials. Preparation of crystalline silicon carbide: germanium alloy (c-SiC:Ge) whose composition was (SixGe0.5-x) C0.50 has been reported by several researchers. Roe et al. reported that preparation of c-SiC:Ge by ion implantation of Ge into bulk SiC and subsequent annealing [12]. They also reported that bandgap of the SiC:Ge (Ge content : 0.3 %) was 8 meV lower than that of SiC. c-SiC:Ge with high Ge concentration was reported by Kouvetakis et al. They deposited polycrystalline Si0.37Ge0.13C0.50 films by
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