Avalanche photodiode (APD) noise dependence on avalanche region width

Conventional noise theory for APDs relates the avalanche noise to the ionization coefficients using McIntyre's[ 11 noise theory. For the lowest excess noise factor (F), the material should have widely disparate ionization coefficients and the carrier type with the larger ionization coefficients should be injected. Unfortunately most conventional 111-V' s have ionization coefficient ratios k=P/a close to unity and efforts to enhance k have mainly concentrated on MQW structures.