Temperature dependence of carrier traps in high sensitivity HARP photoconductive film

Abstract

AbstractAmorphous selenium (a‐Se) avalanche multiplication photoconductive film, what we call HARP (high‐gain avalanche rushing amorphous photoconductor) photoconductive film, has been investigated for the purpose of reporting breaking news at night and producing nature and science programs. The purpose of our work is to develop more sensitive HARP films with high reliability. 15‐μm‐thick HARP film with an avalanche multiplication factor of about 200 that is thicker and more sensitive than the previous 8‐μm‐thick one has been studied. However, the thick film has a problem that defects easily occurred during shooting of intense spot lights. The defects are caused by trapped electrons which makes an enhanced internal electric field around the incident light side interface of the film. Defects are suppressed by operating the film at high temperatures, because the thermal energy releases the trapped electrons. This paper describes the relationship between the defect occurrence and the temperature dependence of carries trap in the film. To investigate it, the defect occurrence and dark current characteristics were measured. As a result, it was found that the number of released electrons exceeds that of trapped ones at temperatures over 28.5 °C and that defect occurrence is suppressed by operating the film at over 27.5 °C. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)