Charge carrier transport anisotropy in ultrananocrystalline diamond films

The optoelectronic properties of ultrananocrystalline diamond films (UNCD) grown using N2=0 and 5% in the deposition gas mixture, are investigated by transient photocurrent measurements under nanosecond light pulses, both in planar and sandwich contact arrangements. Independent of contact configuration and N2% value, very similar characteristic times in the 6-7 ns range are detected in the nanosecond range, reflecting a homogeneous distribution of states responsible for such decay times. On a longer time scale, nitrogen addition appears to slow down carrier transport promoting trapping and detrapping processes responsible for single and two power law photocurrent decays in films deposited using N2=5% for sandwich and planar contact arrangements, respectively. Such a result suggests a nitrogen induced transport anisotropy tentatively related to structural modifications occurring at relatively low N2%.