ZnTe growth has been investigated, using (100), (110) and (111) Zn and Te substrates, by Ar +-ion laser-assisted metal organic vapor phase epitaxy at atmospheric pressure. For the (100)-oriented substrate, the growth rate of the epitaxial layer is dramatically enhanced under illumination. The quantum yield for forming ZnTe molecules by photons is calculated to be as high as about 3%. From the relationship between the transport rate of source material and the growth rate, it has been concluded that both the diethyltelluride and the dimethylzinc which are used as source materials become decomposed by illumination. On the other hand, for other substrate orientations, the effect of illumination upon the growth rate has hardly been observed. Hence, source gas molecules are effectively decomposed on the (100) surface under illumination. Epitaxial layers of good quality can be obtained at low substrate temperature by using the (100) substrate.