Dependency of organic phototransistor properties on the dielectric layers

Abstract

Organic phototransistors with pentacene semiconductor and ${\mathrm{Ta}}_2{\mathrm{O}}_5$ or polymethyl methacrylate (PMMA) dielectric layer have been investigated. It was found that the phototransistor properties strongly depend on the dielectric layer. Under a broadband light with $10\mathrm{mW}∕{\mathrm{cm}}^2$ , the sensitivity of the ${\mathrm{Ta}}_2{\mathrm{O}}_5$ based transistor is much higher than that of the PMMA based transistor. For ${\mathrm{Ta}}_2{\mathrm{O}}_5$ based transistor, the photosensitivity (the ratio of photocurrent to dark current) and the threshold voltage shift are 4000 and $13.5\mathrm{V}$ , respectively. While for PMMA based transistor, the corresponding values are only 0.5 and $2.9\mathrm{V}$ , respectively. That large difference is attributed to the electron trapping ability of ${\mathrm{Ta}}_2{\mathrm{O}}_5$ .