Generation of Free Carriers in Photoconducting Anthracene. I

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Abstract
The source of free carriers in photoconducting anthracene was determined from an investigation of the spatial distribution of trapped electrons. Free carriers are generated in the bulk in addition to electrons being injected into the anthracene at the negative electrode. The bulk generated carriers cannot come from an intrinsic process which simultaneously yields a free electron and a free hole. A tentative extrinsic model for the generation of free carriers is proposed in which electrons are injected at the negative electrode, free holes and trapped electrons are generated by the incident radiation in the bulk at impurities or other defects, and free holes are generated by the incident radiation at the positive illuminated electrode. On the basis of these results, one concludes that anthracene is an extrinsic rather than an intrinsic photoconductor.