Wavelength dependence of multiplication noise in silicon avalanche photodiodes

Theoretical and experimental results on wavelength dependence of multiplication noise in silicon avalanche photodiodes are described. When the photodiode has a p-n
⁺
-junction and is illuminated from the n
⁺
-side, multiplication noise increases by decreasing optical wavelength. Effective ionization coefficient ratio k
eff
is equal to
k
exp (
2Kw_{a}
) for a uniform junction electric field, where
k
is the ratio of ionization coefficients of electrons α and holes β. The multiplication noise depends on the product of optical absorption coefficient
K
and the avalanche-region width w
a
. Calculations show that there exists an optimum w
a
for minimizing multiplication noise at a given wavelength. Theoretical results are shown to agree with results of experiments on diodes with a low-high-low impurity profile. Measured ionization coefficient ratio
k
values are 0.04 and 0.08 at 0.811- and 0.633-µm wavelength, respectively.