Effect of chlorine on xerographic properties of a-Se:Te alloys

Abstract

Amorphous selenium (a-Se) has an optical bandgap of ∼2.1 eV and a photogeneration efficiency close to unity at ∼2.7 eV which makes it sensitive to the blue region of the visible spectrum. Alloying with tellurium reduces the bandgap and hence increases the photosensitivity towards longer wavelengths. Experimental results have already been reported to show that charge acceptance, residual voltage, dark decay rate and drift mobility are all sensitive to tellurium. Charge acceptance and carrier drift mobilities decrease with tellurium whereas dark decay rate increases. All these effects are undesirable in xerography. Transient photoconductivity and residual voltage measurements were carried out to investigate the effect of a small chlorine addition on the xerographic properties of a-Se∶Te alloys. Results will be presented to show that chlorine improves the residual voltage and charge acceptance. Transient photoconductivity data on hole transport shows that the xerographically important parameter of carrier range is also improved. Hole drift mobility shows a weak field dependence of the form μ _h ≃ E _n where the index n is sensitive to chlorine. No electron transport could be detected in any of the samples. These results are interpreted in the framework of shallow-trap controlled transport.