Middle wavelength infrared graphene photodetectors with low dark-current and high responsivity

Abstract

Graphene infrared (IR) photodetectors are promising devices that take advantage of the unique optoelectronic properties of graphene, such as broadband light absorption, rapid response, and high chemical stability. Despite its advantages, graphene has a low absorbance of 2.3%, which limits its photoresponsivity. We have previously reported the responsivity enhancement of graphene middle wavelength IR (MWIR) photodetectors using the photogating effect. The photogating effect is induced by photosensitizers located around the graphene channel that generate a large electrical change. The MWIR photoresponse with the photogating effect was enhanced by 100-fold relative to conventional graphene field-effect transistors (FETs). Although our graphene FETs using photogating exhibited ultrahigh responsivity, the dark current was extremely high, as in the case of conventional graphene FETs, because the normally-OFF operation cannot be realized in graphene. Therefore, reducing the high dark current is essential for applying graphene photodetectors to IR applications. We demonstrate dark current reduction and high responsivity MWIR light detection in graphene MWIR photodetectors. The devices consist of graphene FETs with a carrier injection region. The dark current is reduced by applying a bias voltage. The photocarriers injected into the graphene are amplified by the photogating effect induced in the graphene/insulator region. The dark current of the devices was significantly suppressed compared with that of conventional graphene FETs. The photoresponse characteristics were investigated for devices of different structure sizes. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.