Schottky barrier photodiodes with antireflection coating

Schottky barrier diodes can be used for fast and efficient photodetectors if the incident light is coupled into the depletion layer of the diode and if electron-hole pairs are created by the internal photoelectric effect in the depletion layer. Fast response of the diode is achieved by designing a Schottky barrier with a small RC product. High quantum efficiency is obtained by coupling the light through a thin metal layer into the depletion region of the diode and by using an antireflection coating on the metal layer for matching the incident light beam. Schottky barrier photodiodes have been made with thin semitransparent gold layers on n-type epitaxial silicon and with zinc sulfide as an antireflection coating. A net quantum efficiency of 70 percent has been achieved at the He-Ne laser wavelength of 6328 Å. The pulse response of packaged diodes with 0.5-nanosecond wide pulses shows a symmetrical pulse shape with only small distortion due to carrier diffusion and reactance in the completed package. The diode structure is suitable for detector arrays. It is also useful for optical time domain reflectometry. The technique of coupling light through metal layers can be extended to other optical devices which require efficient transfer of radiation into a semiconductor through conducting electrodes.