Growth of micro-crystalline Si:H and (Si,Ge):H on polyimide substrates using ECR deposition techniques

We report on the growth of good quality micro-crystalline Si:H and (Si,Ge):H films on polyimide substrates using a remote plasma ECR deposition technique. We find that under conditions that lead to significant ion bombardment of the substrate, the films are microcrystalline even at relatively low deposition temperatures of about 250 C. A critical factor in inducing microcrystallinity is the presence of a metal coating layer on polyimide. In the absence of such a coating, the films are amorphous, probably because the uncoated polyimide substrate charges up and prevents any further ion bombardment. The quality of the films was measured using both Raman spectroscopy and by studying the activation energy and low-energy absorption coefficient of the films. The sub gap absorption coefficient was found to follow the crystalline Si absorption curve quite well. The addition of germane to the gas phase shifted the absorption curve to smaller energies.