Surface States on a-Si:H,F Grown from SiF4 and H2

We describe a detailed study of surface states on a-Si:H, F films deposited by DC-plasma from SiF4 and H2. In the a-Si:H, F growth from these source gases, the density of surface states (Nss) and the Urbach Energy (Eu) show a reciprocal relation, meaning that the film grown with less bond distortion is accompanied by a higher density of surface states. These surface states can be reduced by keeping the films at growth temperature after termination of growth; immediate cooling produces a high density. This suggests that bonds can rearrange on or near the film surface at growth temperature, after growth termination. Nss can be made as high as l×1014 cm−2. The surface states can be measured by optical subgap absorption, but do not give an ESR signal. A high density of these surface states lowers the Pd-Schottky barrier height. Time-of flight electron collection data show that the surface states act as deep electron traps, located at about 0.4eV below the conduction band edge. We present and discuss other experimental results to help understand these nature of the surface state on a-Si:H, F.