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1153-A17-07

Phosphorus and Boron Doping Effects on Nanocrystalline Formation in Hydrogenated Amorphous and Nanocrystalline Mixed-Phase Silicon Thin Films C.-S. Jiang, Y. Yan, H.R. Moutinho, and M. M. Al-Jassim National Renewable Energy Laboratory (NREL), Golden, CO 80401 B. Yan, L. Sivec, J. Yang, and S. Guha United Solar Ovonic LLC, Troy, MI 48084 Abstract We report on the effects of phosphorus and boron doping on the microstructure of nanocrystallites in hydrogenated amorphous and nanocrystalline mixed-phase silicon films, using Raman spectroscopy, secondary-ion mass spectrometry, cross-sectional transmission electron microscopy, atomic force microscopy, and conductive atomic force microscopy. The characterizations revealed the following observations. First, the mixed-phase Si:H films can be heavily doped in ~1021/cm3 by adding PH3 and BF3 in the precursor gases. Second, the intrinsic and doped films can be made in a similar crystalline volume fraction by adjusting the hydrogen dilution ratio. The hydrogen dilution ratio is much higher for P-doped films than for the intrinsic film with the similar crystallinity. Third, the doping significantly impacts the nanostructures in the films. Nanograins aggregate to form cone-shaped clusters in the intrinsic and B-doped films, but isolate and randomly distribute in amorphous tissues in the P-doped films. The cones in the intrinsic and Bdoped films are also different. The cone-angle is smaller and the nanograin density is lower in the Bdoped films than in the intrinsic films. These P- and B-doping effects on the nanocrystalline formation are interpreted in terms of diffusion of Si-related radicals during film growth. Introduction Hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) thin films have attracted great interest in photovoltaic devices and large-area thin-film electronics. A common technique for fabricating a-Si:H and nc-Si:H films is plasma-enhanced chemical vapor deposition (PECVD), which decomposes SiH4 or Si2H6 molecules and deposits Si radicals on foreign substrates. One of the advantages in fabricating Si:H-based thin-film devices is that the n- and pdoped layers can be produced during film growth by adding phosphorous- or boron-containing gases. High-performance solar cell devices have been successfully fabricated and manufactured by adding PH3 in the n-layer and BF3, (CH)3B, or B2H6 in the p-layer. Therefore, P- and B-doping effects on the structural and electronic properties of the films are of primary importance in fundamental material study and industrial applications. Many studies on the doping effects concentrate on macroscopic properties of the films [1–4]. In this study, we investigate the doping effects on microstructures of the films. We chose mixed-phase Si:H films because the amount of nanograins in the materials is easy to characterize [5,6]. In a-Si:H film, the nanostructured component is too low to be found; but it is too high in nc-Si:H to distinguish the changes induced by doping. In PECVD, hydrogen dilution is the