EFFECTS OF PRESSURE AND HYDROGEN DILUTION ON GAP-STATE DEFECTS IN A-SIC-H

By using Photothermal Deflection Spectroscopy(PDS), the optical absorp tion was measured in amorphous silicon-carbon alloys. The Urbach energ y E(0) and defect density N-D were deduced in the films. The samples w ere prepared by the technique of Plasma Enhanced Chemical Vapor Deposi tion(PECVD) from silane (SiH4) and methane (CH4). Two series of sample s were studied. The first one was prepared by varying the pressure fro m 0.35 to 0.7 mbar in deposition chamber and for which we find a decre ase of E(0) when E(g) increases, while the defect density is unchanged . The second serie was made by dilution in hydrogen. The effect of dil ution is to reduce considerably E(0) and N-D in the material.