Drift mobility measurements in a-C:H films by time-resolved electroluminescence

Carrier transport mechanism has been studied in thin insulating hydrogenated amorphous carbon (a-C:H) films. The layers were prepared by plasma polymerization of methane (CH4) at a frequency of 20 kHz. Electron mobility was derived from time-resolved luminescence experiments. Between the application of a rectangular voltage pulse and the first appearance of electroluminescence (EL) a time lag exists, which depends on the pulse height. Transit times are in the order of 10−3 to ∼10−6 s in a voltage range between 10 and 25 V. And the estimated electron mobility varies accordingly from 8×10−8 to ∼10−6 cm2/(V s). The field dependence of the carriers mobility is characteristic of Poole–Frenkel-detrapping conduction model, and thus confirms the results obtained by dc experimental data.