Chemical vapor deposition (CVD) is an effective method for the growth of large scale two-dimensional materials. However, high density of vacancy defects are inevitably generated in the CVD process, which affects the photoelectric properties of the materials. In this work, millimeter-scale and atomic-thick WS2 membranes were directly grown on p-type Si (111) substrates using an alkali metal halide-assisted CVD method. Er-doped WS2 films (WS2(Er)) were achieved by adding saturated ErCl3 powders in the tungsten sources. Optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, photoluminescence and Raman spectroscopy techniques were used to characterize the materials systematically. The results show that the fluorescence intensity of WS2(Er) films increase by an order of magnitude compared to pristine WS2, and the central wavelength is significantly red-shifted. Fluorescence tests show that the fluorescence characteristics of WS2 grown on Si substrates show a significant charge transfer effect compared to that of WS2 on SiO2 substrates. The photoelectric test results of WS2 and WS2(Er) field effect transistors based on SiO2 substrate show that the optical responsiveness of WS2(Er) field effect transistors is 4.015 A/W, and the external quantum efficiency is 784%, both of which are more than 2 000 times that of pristine WS2 devices under the same conditions. This work has significance for research of rare earth doping in 2D materials.