Well-oriented zinc oxide nanorods (ZnO NRs) arrays have been grown by low temperature chemical bath deposition on seeded substrates. A gold thin film has obliquely been deposited by DC magnetron sputtering on the ZnO NRs array. The structure, mophology/ chemical identity, vibrational identity have been studied by X-ray diffraction (XRD), field effect- scanning electron microscope/ energy dispersive X-ray spectroscopy (FE-SEM/EDX) and Raman spectroscopy, respectively. The FCC structure of Au is formed on vertically oriented ZnO NRs-array. The wavelength dependent photocurrent of ZnO NRs array-Au heteronanostructure (HNS) was evaluated by photogain response under red, green and blue laser illuminations. Surface plasmon excitation activates selective response to green laser exposure. An analytical dispersion formalism has been constructed to fit experimental absorption spectrum over wide spectrum range and to extract precise bandgap energy, subband tailing, dielectric constant and carrier effective mass. The proposed model exploits the Frouhi–Bloomer (FB) parameterization and Gaussian oscillator dispersion to the complex dielectric function for Au decorated ZnO NRs array. Sharp variation in the optical absorption around the bandgap edge and the absorption behavior beyond the bandgap edge are covered as well. It is surprising that the surface plasmon resonance (SPR) is included without new formalism. The new model has been satisfactorily tested on CuO optical absorption.