Design considerations for high-current photodetectors

This paper outlines the design considerations for gigahertz-bandwidth, high -current p-i-n photodiodes utilizing In GaAs absorbers. The factors being i nvestigated are photodetector intrinsic region length, intrinsic region dop ing density, temperature effects, illumination spot size, illumination wave length, frequency, and illumination direction. Space-charge calculations ar e used to determine optimal device geometry and conditions which maximize s aturation photocurrent, A thermal model is developed to study the effects o f temperature on high-current photodetector performance. The thermal and sp ace-charge model results are combined to emphasize the importance of thin i ntrinsic region lengths to obtain high current. Finally, a comparison betwe en surface-illuminated p-i-n structures and waveguide structures is made to differentiate between the problems associated with achieving high current in each structure and to outline techniques to achieve maximum performance.