A method of preparing a semiconductor film on a substrate is disclosed. The method includes arranging an insulating substrate in a deposition chamber and depositing a semiconductor film onto the insulating substrate using ion beam deposition, wherein a temperature of the insulating substrate during the depositing does not exceed 250.degree. C. The method can produce a thin film transistor. The disclosed ion beam deposition method forms, at lower temperature and with low impurities, a film morphology with desired smoothness and grain size. Deposition of semiconductor films on low melting point substrates, such as plastic flexible substrates, is enables.