Electrical properties of amorphous semiconductor selenium and its alloys: I. Monolayers

Abstract

Various monolayer a-Se-based photoreceptor devices were fabricated by vacuum evaporation and their electrical properties were investigated. Three experimental techniques, namely xerographic time of flight (XTOF), electroded time of flight (TOF) and xerographic discharge were used to determine the drift mobility, carrier lifetime, dark decay and residual voltage. Where possible, these measurements were carried out as a function of applied field and composition, namely As-0.3 wt%, Te up to 17 wt% and Cl up to 60 ppm. The addition of As or Te alone reduced both hole and electron drift mobilities and increased the carrier lifetime. Both XTOF and TOF experiments showed a trap-limited response for electron transport in Se +Cl and Se:Te + Cl systems. The addition of As was found to restore the electron response in these photoreceptors. The drift mobility in all Se-based systems was found to be field dependent, satisfying the algebraic relation p a Y " where n is a constant varying from 0.03 (for electronic mobility in a-Se) to 0.47 (for electron response in a-Se + 17 wt% Tel. Xerographic discharge measurements showed that alloying a-Se with Te increases the dark decay, due to a bulk thermal generation process. Analysing of dark-decay curves indicates that the volume density and energy spread of the mid-gap localised states in a-Se increases with the Te content. The repetition of the xerographic cycle over a number of times leads to the saturation of the residual voltage which was used to calculate the concentration Nt of deep hole traps. The results showed that the addition of Te increases N , from about 1.9 x l O " C ~-~ for a-Se to 7 x l 013 cm-3 for a-Se + 8 wt% Te. From the charge transport data and saturated residual voltage measurements, the hole capture coefficient in a-Se was estimated to be about 1 .O x 1 O-' c& S" .

Charge transport and electron-hole-pair creation energy in stabilized a-Se x-ray photoconductors

“…The electron mobility exhibits a slight power-law field dependence of the type µ e ∝ F n , where n was experimentally determined to be n ≈ 0.1, which is quite small. A similar µ ∝ F n type of behaviour has also been reported for other a-Se alloys (Juhasz and Vaezi-Nejad 1985, Pai 1974, Vaezi-Nejad and Juhasz 1987a. A systematic study of the field dependence of µ e will be reported separately.…”

Electrical properties of amorphous semiconductor selenium and its alloys. II. Heterojunction multilayers

“…previous publication [5]. Results of xerographic dis-However, as described in a previous paper [ 5 ] , increase charge measurements on double layers have already in Te leads to higher thermal carrier generation and been described by one of the authors [ 6 ] .…”

“…previous publication [5]. Results of xerographic dis-However, as described in a previous paper [ 5 ] , increase charge measurements on double layers have already in Te leads to higher thermal carrier generation and been described by one of the authors [ 6 ] . The purpose results in higher dark discharge and less stable electrical of this paper is firstly to discuss the preparation and properties.…”

“…Xerographic time of flight and conventional time of flight experiments were carried out under small signal conditions to determine hole and electron drift mobilities. As described previously [5] optical excitation was used to inject charge carriers into the samples. Transient current signals exhibited interesting fielddependent features which are described in the following section.…”

TexSe1–x Photodiode Shortwave Infrared Detection and Imaging

“…[61,62] It is thus difficult for Te thin film to form an effective p-n junction with another highly n-doped partner. Se has a wide bandgap (E g ) of −1.8 eV, [63][64][65] enabling to increase the bandgap of Te x Se 1-x alloy and decrease the hole density (Table S1, Supporting Information). According to the relationship between E g and x, Te 0.7 Se 0.3 is selected because it has a suitable bandgap of 0.74 eV for an infrared photodetector.…”