Ultrafast silicon interdigital photodiodes for ultraviolet applications

Abstract

Conventional ultrafast photodetectors in use today generally have very small quantum efficiencies in the ultraviolet where the absorption length is very short. To extend the spectral range further into the ultraviolet, a strong electric field is required right at the surface on which the photons are incident. One method of achieving the required field is the use of two sets of interlocked metal digits, forming two back-to-back Schottky barriers on the surface of the semiconductor. Since both contacts are on the top surface, a thin semiconducting film on an insulating substrate can be used, greatly reducing depletion capacitance.We report a preliminary investigation of the potential of such devices using silicon on sapphire as an examplar material. Results are presented that show that capacitances of approximately 1 pF were obtained for devices with an area in the order of 10−3 cm2. These devices had a measured response time of less than 100 ps and measured quantum efficiencies at 337 run in the order of 10%, without the benefit of an antireflective coating.These preliminary results show that this type of device has excellent potential as an ultrafast, ultraviolet photodetector.