Anisotropic drift mobility in hydrogenated amorphous silicon

The dependence upon the electric field direction of the electron photocarrier transient drift mobility was measured in amorphous hydrogenated silicon (-Si:H) using transient photocurrent and time-of-flight spectroscopy. In contrast with the frequent assumption of microscopically isotropic transport in noncrystalline materials, the measurements indicate that the electron drift mobility is anisotropic in -Si:H. The ratio of axial measurements (along the growth axis) and planar measurements (parallel to the surface) can exceed an order of magnitude. Certain problems with previous transport-based characterizations of -Si:H may be resolved by anisotropic mobility effects.