Abstract: The resonant cavity with p-i-n structure, which is to enhance the quantum efficiency of lateral photoelectric effect, is designed for position sensitive detector. The top mirror is a one-dimensional defect photonic crystal, and the bottom mirror is a distributed Bragg reflector (DBR), while the part of between the two mirrors is the active medium. The transmission of defect photonic crystal is obtained by transform matrix method. Because of the high reflectivity of top and bottom structures, the transmitted resonant guided mode of defect photonic crystal would be limited in active medium. The quantum efficiency of active medium is deduced by analyzing the equivalent mode of resonant cavity. The results of numerical simulation show that the quantum efficiency is enhanced by the resonant guided mode.