Physical asymmetrical Metal / AZO / SiOx / n-Si / Metal devices in semiconductor-insulator-semiconductor (A-SIS) framework were investigated for their anormaly current-voltage characteristics under light irradiation. The devices showed a normal rectifying character in dark but manifested a peculiar current-voltage feature at reverse bias under illumination. Considering the change of energy band structure at the reverse electric field, it was found that the transport of electrons was mainly dominated by the thermionic emission and quantum tunneling at low voltage. With the increase of the reverse bias, the electrons were able to tunnel through the reduced barrier of ultra-thin SiOx layer (<1nm) and an effective triangle-like barrier of silicon. An appropriate simulation of the J-V relationship demonstrated that the photons acting as the assisted part magnified the reverse current density, and the thickness of SiOx layer managed the amount of the reverse saturation current.