Highly conductive n+ hydrogenated microcrystalline silicon and its application in thin film transistors

n(+) muc-Si:H films were deposited using 13.56 MHz plasma enhanced chemical vapor deposition from a gas mixture of silane, phosphine, and hydrogen. To study the effect of deposition conditions and thickness dependence on film properties, and to optimize deposition regimes, we varied the rf power and doping ratio for two different hydrogen dilutions. The film properties were investigated using Raman, x-ray diffraction, secondary-ion-mass spectroscopy, and optical transmittance measurements, as well as dark conductivity. The growth mechanism for a formation of n(+) muc-Si:H is explained in terms of a hydrogen dilution effect using the combination of surface diffusion and selective etching models. The optimal conductivity [25 (Omegacm)(-1)] 50 nm n(+) muc-Si:H film was obtained with 99.6% hydrogen dilution of silane. Thin film transistors with this n(+) muc-Si:H ohmic contact layer demonstrate a device mobility of 0.9 cm(2) Ns, a threshold voltage of 3 V, an ON/OFF current ratio of above 10(7), a subthreshold slope of 0.5 V/dec, and a leakage current of the order of 10-13 A. (C) 2004 American Vacuum Society.