Ultra-low noise avalanche photodiodes with a "centered-well" multiplication region

We report avalanche photodiodes with a "centered-well" multiplication region that have achieved high gain, low noise, and low dark current. The multiplication region consists of an ∼80 nm-thick Al
_0.2
Ga
_0.8
As layer sandwiched between two thin (10∼20 nm) layers of Al
_0.6
Ga
_0.4
As. Monte Carlo simulation shows the beneficial effect of spatial modulation of the ionization rates in this structure compared to homojunctions.