•Uniaxial p–n junction diode in GaN nanorod is made by Hydride vapor phase epitaxy method.•The p–n junction diode property is clearly observed from the fabricated uniaxial p–n junction nanorod GaN nanorod.•Graphene is used as a current spreading layer to reduce the lateral resistance up to 700 times when compared with the commercial sapphire substrate, which is clearly explained with the aid of an equivalent circuit.•Kelvin Force Probe microscopy method is employed to visualize the p- and n- regions in a single GaN nanorod. Mg doped GaN nanorods were grown on undoped n-type GaN nanorods uniaxial on monolayer graphene by hydride vapor phase epitaxy (HVPE) method. The monolayer graphene used as the bottom electrode and a substrate as well provides good electrical contact, acts as a current spreading layer, well suitable for the growth of hexagonal GaN nanorod. In addition it has a work function suitable to that of n-GaN. The formed p–n nanorods show a Schottky behavior with a turn on voltage of 3V. Using graphene as the substrate, the resistance of the nanorod is reduced by 700 times when compared with the case without using graphene as the current spreading layer. The low resistance of graphene acts in parallel with the resistance of the GaN buffer layer, and reduces the resistance drastically. The formed p–n junction in a single GaN nanorod is visualized by Kelvin Force Probe Microscopy (KPFM) to have distinctively contrast p and n regions. The measured contact potential difference of p-and n-region has a difference of 103mV which well confirms the formed regions are electronically different. Low temperature photoluminescence (PL) spectra give evidence of dopant related acceptor bound emission at 3.2eV different from 3.4eV of undoped GaN. The crystalline structure, compositional purity is confirmed by X-ray diffraction (XRD), Transmission and Scanning electron microcopies (SEM), (TEM), Energy dispersive analysis by X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS) as well.