Deposition of Amorphous and Microcrystalline Si,C Alloy Thin Films by a Remote Plasma-Enhanced Chemical-Vapor Deposition
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DEPOSITION OF AMORPHOUS AND MICROCRYSTALLINE Si,C ALLOY THIN FILMS BY A REMOTE PLASMA-ENHANCED CHEMICAL-VAPOR DEPOSITION PROCESS C. WANG, G. LUCOVSKY AND R.J. NEMANICH Departments of Physics, and Materials Science and Engineering North Carolina State University, Raleigh, NC 27695-8202 ABSTRACT We have extended the remote PECVD process to the deposition of intrinsic and doped, amorphous and microcrystalline silicon,carbon alloy films, a-Si,C:H and gc-Si,C, respectively. The electrical and optical properties of a-Si,C:H deposited by remote PECVD are comparable to those of films deposited by the glow discharge or GD process. The degree of crystallinity in the lc-Si,C alloys, as determined from the relative intensities of crystalline and amorphous features in the Raman spectra, is lower than that of gc-Si films deposited under comparable deposition conditions. The Raman spectra indicate that the crystallites in the jic-Si,C alloys are Si, while the infrared measurements establish that the intervening amorphous component is an a-Si,C:H alloy. INTRODUCTION The electrical and optical properties of amorphous and microcrystalline silicon,carbon alloy films deposited by GD technique can be tailored for specific device applications by varying the relative concentrations of Si and C. The intrinsically wider band-gaps of a-Si,C:H and lic-Si,C relative to a-Si:H and gic-Si, respectively, combined with the ability to dope the Si,C alloys n-type and p-type has made them important components in high efficiency amorphous silicon solar cells [1], and in electroluminescent devices [2]. We have previously established that device-quality intrinsic and doped a-Si:H and gxc-Si can also be deposited by an alternative plasma-assisted deposition process, remote PECVD, and that these films can also be incorporated into device structures [3,4,5]. In this paper, we extend these studies of remote PECVD films to the deposition of intrinsic and doped a-Si,C:H and l±c-Si,C. The amorphous films are produced by remotely exciting down-stream injected SiH4-CH4 source gas mixtures, and the gic-Si,C films are produced by adding H2 downstream as well. We have also been able to deposit n-type and p-type a-Si,C:H and l±c-Si,C alloy films by introducing the respective dopant atom source gases, PH3 and B2H6, downstream from the plasma generation region. The structural, electrical and optical properties of these a-Si,C:H and gcSi,C films have been investigated and are discussed below. FILM DEPOSITION The remote PECVD deposition system used for film preparation in this study has been described elsewhere [3]. The deposition conditions for producing device quality a-Si,C:H films are essentially the same as those used for the deposition of device quality a-Si:H films, except that the C-atom source gas CH4 is introduced downstream along with the Si-atom source gas SiH4, and the combined flow of the SiH4+CH4 mixture is maintained at a level comparable to the flow of SiH4 for the a-Si:H depositions. We have defined the SiH4 fraction of this Si- and C-atom source gas
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