On Image Charge Induced Barrier Lowering in Graphene–Semiconductor Contacts

Graphene has been extensively studied as highly flexible and optically transparent contacts in semiconductor devices, such as photodetectors, solar cells, and light emitting transistors. A Schottky barrier forms at the interface between graphene and semiconductor, whose height has an exponential impact on the current. In this work, image-charge-induced barrier lowering (BL) in graphene-semiconductor contacts is examined and compared to that in metal Schottky contacts. The results show that despite graphene being a semimetal with vanishing density-of-states at the Dirac point, the image-charge-induced BL can be significant. Even in an undoped graphene-semiconductor contact, the BL value can be more than 50% of that of a metal Schottky contact. The ratio of BL in a graphene-semiconductor contact to that in a metal-semiconductor contact increases as the graphene doping density increases and as the semiconductor dielectric constant decreases. An empirical expression for estimating the image-charge-induced BL in graphene-semiconductor contacts is provided.