Transient-photocurrent studies ina−Si:H

Abstract

We present a detailed study of carrier transport in sputtered $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ with the use of the time-of-flight technique. Charge-collection experiments reveal that total charge collection must take place to enable the extraction of reliable dispersion parameters. Under this condition the dispersion parameters accurately follow the predictions of a multiple trapping and release transport process. By integration of the current transients we derive values of the ${\ensuremath{\mu}}_{D}{\ensuremath{\tau}}_{D}$ product for samples having a range of deep-state densities and also obtain the capture cross section of the dominant defect. Upon phosphorus doping the electron carrier lifetime increases; furthermore, changes in the dispersion parameters suggest that the conduction-band-tail---state distribution is altered with respect to the undoped material. We also present measurements of photocurrents made with the use of electrode co-planar geometry and suggest that carrier loss to deep states dominates the response at room temperature.