By observing two-photon response and anisotropy of the light-induced voltage in Al-Si Schottky barrier potential,it is certified from the experimental and theoretical analysis that the built-in electric field generated by the Schottky barrier potential will induce the phenomena of optical rectification in Si photodiode.Thus,it is deduced that there must be double-frequency absorption caused by phase-mismatch in the mechanism of two-photon response of Si photodiode.If the intensity of the built-in electric field is strong enough,the double-frequency absorption will be the main factor of the two-photon response,which is different from the conventional opinion that the two-photon response is just the two-photon absorption.
