High Gain $\times$ Bandwidth Product Over 140-GHz Planar Junction AlInAs Avalanche Photodiodes

This letter demonstrates a planar junction GalnAs-AlInAs avalanche photodiode using back-side illumination through thinned InP substrate covered with chemical vapor deposition SiN
_x
antireflection coating. The combined properties of very low dark current (
I

_dark
(
M
= 0) = 17 nA), low excess noise factor (f(M = 10) = 3.5), and high gain x bandwidth product over 140 GHz were simultaneously achieved with a high primary responsivity of 0.95 A/W at 1.55 mum.