A-SIH 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 (mu(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 x 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 mu(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 eta almost-equal-to 1. In the end, two possibilities of explaining the discrepancy in comparison with Spear's work are discussed.