Depth Profiling of Light-Induced Defects in Hydrogenated Amorphous Silicon by Transient Photocurrent Spectroscopy

Abstract

The sensitivity of transient photocurrent measurements to the spatial location of native and metastable electronic defects in hydrogenated amorphous silicon films is demonstrated. The technique utilises red and green laser excitation to generate excess carriers in the bulk and at the surfaces of the film, respectively. In annealed films the defect density is found to be higher in the surface regions. Following white light soaking, the metastable defect density at the surface at which the light is incident is greater than that in the bulk, which in turn is greater than that at the exit surface. This is attributed to the white light absorption profile within the film. Green light soaking creates metastable defects at the incident surface, with the bulk of the film largely unaffected.