Enhanced photoresponse in graphene/Al doped ZnO nanorod junction

The current study examines the performance of graphene/Al doped ZnO (ZnO:Al) heterojunction photodetectors by variation in carrier concentration of ZnO layers. This is controlled by variation of O₂ percentage in growth of ZnO:Al layers produced by reactive sputtering within a small range of O₂ (5–8 %). Under light, the diodes fabricated with ZnO layers deposited at 5 % O₂ exhibit almost linear I–V characteristics, resulting in high photoresponsivity of around 0.08 A/W at 0 V and about 80 A/W at +3 V. Graphene/ZnO:Al junctions that are fabricated using lightly doped ZnO:Al layers deposited at ≥ 6 % O₂ exhibit comparatively poorer photoresponsivity (17 A/W at +3 V) when exposed to light. The responsivity of graphene/ZnO:Al increases from 17 to 95 A W⁻¹ as carrier concentration of ZnO layers rises from ∼10¹⁸ cm⁻³ to ∼5 × 10²⁰ cm⁻³. Carrier concentration induced Schottky barrier height change from 0.57 to 0.75 eV which enhances the responsivity of PDs from 17 to 95 A W⁻¹. Reactive sputtering of ZnO:Al at moderate substrate temperatures allows for technological versatility and scalability, as well as simple control over its carrier concentration. Graphene/ZnO:Al Schottky type diodes appear promising for a variety of device applications beyond photodetector applications.