We report on the photodetection properties of a graphene-oxide-semiconductor (GOS) diode by measuring its current-voltage characteristics under illumination with light-emitting diodes (LEDs). We demonstrate that a GOS structure, with graphene used as a transparent gate electrode to form an inversion layer at the oxide-semiconductor interface, can function as a GOS field-effect transistor operable at low temperatures down to 1.5 K. By investigating the gate tunneling current in a GOS diode with a transistor structure, we find that the dark current is below approximately 0.1 nA at T = 150 K, which is almost two orders of magnitude lower than that in a graphene-semiconductor (GS) Schottky-diode photodetector. Notably, the GOS diode shows a bilateral photoresponse in both forward- and reverse-bias regimes under LED illumination. The photocurrent responsivity R reaches approximately 100 mA/W at T = 150 K with a low bias voltage of approximately − 0.6 V, which is one order of magnitude lower than that applied in a GS Schottky-diode photodetector. We propose that a GOS heterostructure can be made to behave as a p - i - n or an n - i - p diode by manipulating the polarity of the bias voltage applied to the graphene gate. In addition, we quantitatively simulate the key features of the dark current by taking into account the associated bipolar current in graphene along with band-to-trap tunneling and trap-assisted tunneling processes. Our theoretical model sheds light on the mechanism of the bilateral photoresponse of the GOS photodetector. Our work paves the way to engineering hybrid
