a-Si:H electron drift mobility measured under extremely high electric field

The electron drift mobility of undoped a-Si:H is studied by a current time-of-flight method over a broad temperature range (T=35–300 K). A possibility of deducing the drift mobility (${\mathrm{\mu }}_{\mathit{D}}$) from the initial (t=0) value of space-charge-limited current (SCLC) is suggested and verified for T>120 K. In the SCLC case an effect, the so-called pseudotransit, is observed and explained. The drift mobility is deduced at electric fields F>1×${10}^5$ V/cm and low temperatures, T<120 K, not only for a high intensity of illumination (the SCLC case) but also for the ‘‘small-signal’’ case (low-intensity illumination). Both these values are in agreement, and there is no increase of ${\mathrm{\mu }}_{\mathit{D}}$ at T<100 K, as observed by W. E. Spear [in Amorphous Silicon and Related Materials, Advances in Disordered Semiconductors Vol. 1, edited by H. Fritzsche (World Scientific, Singapore, 1989), p. 721]. The strong electric-field dependence of the collected charge is observed at these temperatures and even at 40 K almost full charge collection is reached. This implies that the quantum efficiency η≊1. In the end, two possibilities of explaining the discrepancy in comparison with Spear’s work are discussed.