Defect band distributions in hydrogenated tetrahedral amorphous carbon/crystalline silicon heterostructures

Junction capacitance measurements and voltage-pulse stimulated capacitance transient measurements have been applied to undoped hydrogenated tetrahedral amorphous carbon (ta-C:H)/crystalline-Si (c-Si) heterostructures to deduce the defect densities in as-grown and post-annealed ta-C:H films. Transient capacitance measurements reveal a component corresponding to the emission of carriers out of defect states at the ta-C:H/c-Si interface, and a slower component corresponding to the carrier emission from defect states of interior ta-C:H. The interior defect density of as-grown films was estimated at 1×1018±2×1017 cm−3, decreasing to (6.5±2)×1017 cm−3 for films annealed at 300°C. A Gaussian defect band was identified with activated hole emission with a 0.35 eV activation energy. Steady state admittance measurements indicate two thermal activation processes and have allowed us to determine a defect density of 1×109±2×108 cm−2 at the ta-C:H/c-Si interface.