▎ 摘　　要

Ultraviolet (UV) photodetectors have been fabricated on a graphene/4H-SiC wafer. In this device, the electrical doping in the graphene layer, under the gate, is realized by changing the gate voltage while the optical doping in the graphene layer outside the gate region is realized through the photogenerated carrier injection from SiC, by laser excitation at 325 nm. This kind of dual modulation of optical and electric fields ultimately results in the formation of a planarn-p-norn-n-njunction in the graphene layer. The photoresponse results demonstrate that the planarn-p-njunction is formed at the negative gate voltage, and facilitates negative photoconductivity. Then-n-njunction is formed at the positive gate voltage and facilitates normal photoconductivity. The maximum responsivity, which is attributable to the high photoconductive gain in the planarn-n-njunction, is 254.1A W-1, at drain-source voltage of -3 V and gate-source voltage of 3 V. Based on these results, the estimated lifetime of the electrons in the graphene channel extends greatly to more than four orders of magnitude longer than that in the isolated graphene. The above results prove that this graphene/4H-SiC combined structure possesses great potential in practical UV-detection applications.