Low-noise avalanche photodiodes with graded impact-ionization-engineered multiplication region

A novel impact-ionization-engineered multiplication region for avalanche photodiodes is reported. By pseudograding the multiplication region with materials of different ionization threshold energies, the impact ionization of the injected carrier type is localized, while that of the feedback carrier type is suppressed. Low noise (k/sub eff/<0.1), low dark current, and high gain were achieved.