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A14.1.1

Application of Spectroscopic Ellipsometry and Infrared Spectroscopy for the Real-Time Control and Characterization of a-Si:H Growth in a-Si:H/c-Si Heterojunction Solar Cells Hiroyuki Fujiwara and Michio Kondo Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan ABSTRACT We have demonstrated real-time process control of a-Si:H growth in an a-Si:H/c-Si heterojunction solar cell by spectroscopic ellipsometry (SE). Accurate thickness control of a-Si:H p-i layers with a precision better than ±1 Å has been realized by this technique. From real-time attenuated total reflection spectroscopy (ATR), we find the formation of a porous interface layer with a maximum SiH2-hydrogen content of 27 at.% at the a-Si:H/c-Si interface, although a rather high conversion efficiency of 14.6 % has been obtained in the solar cell. We found that an optimum i-layer thickness for the a-Si:H/c-Si solar cells is consistent with the thickness at which the a-Si:H i-layer growth reaches a steady state after the H-rich interface-layer formation. We have applied SE further to determine the dielectric functions of In2O3:Sn and ZnO:Ga with different carrier concentrations. From the dielectric function analysis, the effective mass m* is extracted. We find linear increases in m* as the carrier concentration of In2O3:Sn and ZnO:Ga increases. The validity of our analyses has been confirmed from excellent agreement between carrier concentrations determined by SE and Hall measurements. The construction of the optical database further enabled us to calculate a reflectance spectrum of the a-Si:H/c-Si solar cell accurately. INTRODUCTION Heterojunction solar cells consisting of hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) have received renewed attention because of their high efficiencies exceeding 20 % [1]. In the heterojunction solar cells, however, real-time thickness control is of significant importance especially for mass production, owing to thin layer thicknesses of a-Si:H layers (~50 Å) and large dependences of solar cell characteristics on the a-Si:H layer thicknesses [2]. For real-time control of semiconductor processing, spectroscopic ellipsometry (SE) provides an ideal tool, as SE offers a non-invasive measurement during processing. In this study, we have demonstrated real-time thickness control of a-Si:H layers in the a-Si:H/c-Si heterojunction solar cells by applying SE. To characterize interface structures in the a-Si:H/c-Si heterojunction solar cells, we have performed real-time infrared attenuated total reflection spectroscopy (ATR). Real-time ATR enables us to investigate SiHn (n=1~3) local structures during interface formation [3]. By performing real-time SE and ATR simultaneously, growth processes and structures of a-Si:H layers can be determined in greater detail. Furthermore, we have applied SE to determine the dielectric functions of In2O3:Sn and ZnO:Ga that have been incorporated in various solar cells. In parti