Abstract: In the method of forming an amorphous silicon film on a substrate supported on an electrode facing a discharging electrode within an evacuated reaction chamber through decomposition of a reacting gas introduced therein and containing at least silicon hydride such as SiH.sub.4 along with or without a doping impurity gas, by glow dicharging developed across the facing electrodes through application of a high frequency (radio frequency) electric power the oppose across, the improvement wherein: the power density of the electric power applied for glow discharging is so set that the ratio of the electric power relative to the discharging surface area of the discharging electrode is 0.3 W/cm.sup.2 or greater, and the ratio F/V of the total flow rate F (l/min.) relative to the volume V (l) of the reaction chamber is 0.01 min..sup.-1 or greater. The resulting a-Si film has a high resistivity in darkness and a large photosensitivity which are suitable for electrophotography.

Abstract: For regulating the vibration frequency of a tuning-fork vibrator to a desired frequency, the tuning-fork vibrator is regulated so that its vibration frequency may become a frequency lower than the desired frequency by a predetermined value, and then the tuning-fork vibrator is regulated so that a difference between proper vibration frequencies of both legs of the vibrator may become smaller than a predetermined value, and further, the vibrator is regulated so that the desired frequency may be reached, while maintaining the difference in the proper vibration frequency smaller than the predetermined value. In this way, the desired frequency can rapidly be attained.