Tunneling-Induced Amplification of Photoexcited Electrons in ITO–Graphene Heterojunction Photodetectors for High-Performance Photodetection

In this study, we investigate the performance of an Indium tin oxide (ITO)–graphene heterojunction photoreactor, fabricated using the RF-sputtering method. The ITO thin film, with a thickness of 23.4 nm and a grain size of 12.5 nm, was deposited onto graphene under an oxygen-to-argon gas ratio of 1:20. The ITO area was precisely controlled using a metal mask, resulting in an ITO–graphene heterojunction structure. The photoreactor exhibited a significant increase in current under forward bias, with a cut-in voltage of 2.8 V and leakage current under reverse bias. Schottky junction characteristics were observed between the ITO and graphene. At −0.2 V bias, the dark current was 0.55 nA/cm², while the device demonstrated high photoresponsivity (1.56 A/W) and photodetectivity (9 × 10¹² Jones). Notably, the device showed tunneling-induced amplification of the photocurrent, approximately 44 times, due to photoelectrons tunneling from the graphene side to the ITO layer. This tunneling effect plays a crucial role in enhancing the device's performance. Additionally, the device demonstrated self-powered operation, with rise and fall times of 0.544 and 0.613 ms, respectively, under modulated light. These findings underscore the potential of ITO–graphene heterojunctions for high-performance photodetectors, with tunneling-induced amplification as a key mechanism for improved photoresponse.