A bias-free, lateral effect position sensor photo-detector

Abstract Lateral effect photodiodes sense the position of a laser beam by measuring the change of current between opposite anodes and a common cathode. They either require a bias current or the current is photogenerated. In either case, their linearity is affected by the non-uniformity of the current distribution between the anodes. We here propose a bias-free, lateral photo-diode, which consists of a resistive layer forming an extended Schottky contact to an intrinsic semiconductor. In our sensor, the photo-generated carriers do not diffuse laterally. Rather, their localization under the laser-beam results in a reduction of the barrier height due to image force effect. An open-circuit voltage appears between two opposite electrodes that is linear with the laser-beam position. A tetra-lateral configuration, with four anodes at the edges of a square-shaped sensor, allows sensing in two dimensions.