Bulk and surface defects in a-Si:H films studied by means of the cavity ring down absorption technique

The sub gap absorption at 1.17 eV in hydrogenated amorphous silicon (a-Si:H) has been measured by means of the ex situ cavity ring down (CRD) absorption technique. The evolution of defects has been studied as a function of film thickness and deposition temperatures. A comparison with the dual beam photoconductivity (DBP) technique shows that the CRD results are systematically higher. Furthermore, it is shown that the CRD technique is sensitive to surface defects and typical surface dangling bond coverages of 2×10-4 up to 6×10-3 are obtained for air-exposed a-Si:H samples depending on the deposition temperature.