Wireilla Scientific Publications
The main speed limitations of standard nanometer CMOS photodiodes are coming from the substrate slow carriers diffusion. Also the capacitance of the photodiode is increasing with technology scaling as the doping is increasing. The PD capacitance must be as low as possible to reduce the high frequency loss of the photocurrent to reach highest possible sensitivity. These demands are partially conflicting; so a trade-off is necessary, especially due to the wavelength dependence of the penetration depth.