High-electric-field transport ina-Si:H. I. Transient photoconductivity

Transient hole currents in hydrogenated amorphous silicon at low temperatures and high fields

“…The reduced value of Qo at 80K may be due to enhanced recombination in the generation layer arising from the low mobility and is observed also in other data (Kocka et al 1990, Nebel et al 1992a). The high-field hole p~t product is only slightly smaller than the electron p~t of (1-3) x lop9 cm2 V-measured at 40 K and at similar fields (Nebel 1991, Kocka et al 1990).…”

“…Further low-temperature time-of-flight (TOF) experiments found that the electron mobility continuously decreases with increasing temperature but is greatly enhanced at high electric fields, above lo5 V cm-' (Kocka et al 1990, 1992, Nebel 1991. Field-enhanced band-tail hopping was shown to explain the data (Nebel, Street, Johnson and Kocka 1992a). Up to now, however, no transient photoconductivity experiments investigating high-field hole transport and thermalization at low temperatures have been reported.…”

“…INTRODUCTION Hole transport in hydrogenated amorphous silicon (a-Si : H) has been widely studied near room temperature (for example Marshall, Street, Thompson and Jackson (1987), Gouldie and Spear (1988) and Nebel and Bauer (1989)). The hole propagation is dispersive below 400 K and a drift mobility ph has an activation energy in the range 300-500meV.…”

High-field electrical conductivity in disordered systems

“…This decrease in the conductivity with ®eld may be linked to that observed in non-crystalline semiconductors (Zabrodskij and Shlimak 1977) and in molecularly disordered polymers (Yuh and Pai 1990, Abkowitz 1992, Novo et al 1993, Van der Auweraer et al 1994, Young and Rule 1994, Borsenberger and Shi 1995, Nemeth-buhin et al 1996.…”

“…Introduction The transport properties of Anderson localized electrons in the presence of high electric ®elds have attracted much attention in theoretical as well as experimental studies. Observations have been made of strong nonlinearities in the ®eld dependences of the conductivity in disordered systems, for example in amorphous semiconductors, such as hydrogenated amorphous silicon (Street 1989, Nebel et al 1992a, b, Cleve et al 1995 and in disordered organic solids, such as molecularly doped polymers, conjugated polymers and organic glasses (Abkowitz et al 1990, BaÈ ssler 1993, Gartstein and Conwell 1995, Dunlap et al 1996, Blom et al 1997, Novikov et al 1998, Bleyl et al 1999, Campbell et al 1999, Yu et al 2000, Kazihiko and Tachiya 2001. In particular, attention has been focused on the ®eld dependence of the conductivity in disordered organic materials.…”