GaN has been widely used in the fabrication of ultraviolet photodetectors (UV PDs) because of its direct wide bandgap of 3.4 eV and excellent thermochemical stability^[1–4]. Typical GaN PD is based on photoconductivity, p–n junction, and Schottky barrier^[5–7]. A metal layer of about 5 nm is commonly used as the transparent conductive layer in GaN PD^[8]. However, this translucent metal has a low transmittance (10% absorption per nanometer), which blocks large amounts of light and reduces photoresponsivity. Moreover, because of low carrier mobility and short carrier lifetime, the photosensitive area of GaN photodetectors is usually limited to about 0.1 mm², which is detrimental to imaging applications^[9]. Graphene has excellent electrical conductivity (extremely high carrier mobility) and outstanding photopermeability from UV to infrared (2.3% per layer of absorption)^[10–12]. Furthermore, graphene is a kind of semi–metal that can form a Schottky junction with GaN^[13]. So it is expected to be a substitute for metal electrodes on GaN PD devices^{[14, 15]}. In addition to the function of transparent conductive electrodes, graphene can be used as an effective current transmission channel^[16]. At the graphene/GaN interface, the photo–generated carriers can be separated due to the built-in electric field. This type of carrier can migrate into graphene to produce a photocurrent^[17]. Due to the high defect density and low conductivity, the performance of conventional GaN-based photodetectors has been partially limited by the efficiency of photocarrier collection. GaN nanowire (NW) arrays can provide larger average current densities of vertical devices^{[18, 19]}. A high-quality GaN nonpolar surface can be obtained without substrate lattice mismatch restriction and the stress release problem of GaN devices can be solved^[20]. At present, GaN or other nanowires are commonly grown directly from the substrate with the down–top mode by molecular beam epitaxy (MBE) or metal–organic chemical vapor deposition (MOCVD)^{[21, 22]}. However, this method is not only expensive but it is also difficult to control the morphology of nanowires. Another way to overcome these drawbacks is a top–down fabrication, using standard photolithography and etching to compose nanowires on a homogeneous film^{[23, 24]}. Vertically aligned semiconductor nanorods (NRs) have been demonstrated in this top–down approach. However, until now, there have been few studies involving graphene and GaN nanorods in photodetectors.