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Characterization of Boron Doped Amorphous Silicon Films by Multiple Internal Reflection Infrared Spectroscopy N. Ross1, K. Shrestha2, O. Chyan1, C. L Littler2, V. C. Lopes2, and A. J. Syllaios2 1 Department of Chemistry and 2Department of Physics, University of North Texas, Denton, TX 75203, USA

ABSTRACT In this study, we employed Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) to characterize chemical bonding structures of boron doped hydrogenated amorphous silicon (aSi:H(B)). This technique has been shown to provide over a hundred fold increase of detection sensitivity when compared with conventional FTIR. Our MIR-IR analyses reveal an interesting counter-balance relationship between boron-doping and hydrogen-dilution growth parameters in PECVD-grown a-Si:H. Specifically, an increase in the hydrogen dilution ratio (H2/SiH4) was found to cause the increase in the Si-H bonding and a decrease in the B-H and SiH2 bonding, as evidenced by the changes in corresponding IR absorption peaks. In addition, although a higher boron dopant gas concentration was seen to increase the BH and SiH2 bonding, it also resulted in the decrease of the most stable SiH bonding configuration. The new chemical bonding information of a-Si:H thin film was correlated with the various boron doping mechanisms proposed by theoretical calculations. INTRODUCTION Thin amorphous silicon and its alloy films are widely used in important commercial applications including thin-film transistor and photovoltaic solar cell. For uncooled microbolometer infrared detectors, optimizing the key properties of film morphology, temperature coefficient of resistance and electrical conductivity is crucial for the detector performance. Extensive characterization has been carried out on the effects of PECVD growth conditions on optical and electrical properties of amorphous silicon [1-4]. However, the chemical bonding structure is less studied. In this work, we have used MIR-IR spectroscopic tool to investigate the chemical bonding of hydrogenated amorphous silicon (a-Si:H) thin film and explore its boron doping mechanism. EXPERIMENT Samples of a-Si:H thin films were grown in a PECVD system using capacitively coupled 13.56 MHz plasmas with the substrate on the ground electrode. Source gases for p-type a-Si:H growth were silane (SiH4) and hydrogen in argon, and boron trichloride (BCl3). MIR-IR was used to characterize the chemical bonding structure differences due to variation of H dilution and B doping during PECVD deposition. MIR-IR utilizes silicon wafer itself as an IR waveguide for attenuated total reflection (ATR) to achieve sub monolayer detection sensitivity [5]. Favorable

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difference of refractive indices of Si wafer and its air interface enables multiple total internal reflections (ca. 80 reflections from a 60 mm Si ATR crystal), which greatly enhances IR measuring sensitivity. The a-Si:H (ca. 50 nm) coated silicon wafers were fabricated on to an ATR optical element (60 x 10 x 0.7 mm, 45° bevel angle) by mechanical polishing [5]. For Si backg