Hydrogenated microcrystalline silicon (mu c-Si:H) thin films were deposited on the glass substrate at the applied electric biases of -200, 0 and +200 V on the substrate holder at the filament temperature of 1700 degrees C and the substrate temperature of 300 degrees C. At the electric biases of -200, 0 and +200 V, the respective growth rate of films was 6.4, 4.7 and 4.1 angstrom/s, the respective root-mean-square (RMS) surface roughness was 27.6. 5.46 and 2.42 nm and the respective optical band gap (E-opt) was 1.75, 1.68 and 1.65 eV. The results indicate that the growth rate could be increased by applying the negative bias whereas the surface uniformity could be improved by applying the positive bias. The dependence of E-opt on the electric bias had some correlation with that of the RMS surface roughness in such a way that E-opt decreases as the RMS surface roughness decreases. (C) 2008 Elsevier B.V. All rights reserved.