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 investigated are photodetector intrinsic region length, intrinsic region doping density, temperature effects, illumination spot size, illumination wavelength, frequency, and illumination direction. Space-charge calculations are used to determine optimal device geometry and conditions which maximize saturation photocurrent, A thermal model is developed to study the effects of temperature on high-current photodetector performance. The thermal and space-charge model results are combined to emphasize the importance of thin intrinsic region lengths to obtain high current. Finally, a comparison between 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.