Voltage-pulse stimulated capacitance transient measurements on a seriesa-Si:H/a-Si, Ge:H devices disclose a large density of hole traps at or very close to the heterojunction interface. The transient signal magnitude is independent of temperature or applied bias, ruling out charge polarization effects or a defect creation process caused by the filling pulse. While the areal density of such hole traps is considerable (within a factor of 2 of1011 cm−2for all samples) these traps do not appear to behave as recombination centers. Also, the treatment of thea-Si:H/a-Si,Ge:H interface during growth can significantly alter the concentration of these traps. ©1997 American Institute of Physics.