Digital Alloy Staircase Avalanche Photodetectors With Tunneling-Enhanced Gain

We report digital alloy Al
$_{x}$
In
$_{1-x}$
As
$_{y}$
Sb
$_{1-y}$
/GaSb staircase avalanche photodiodes (APDs) that operate using carrier-trapping induced tunneling gain. A model describing carrier injection and escape from non-square quantum wells is presented to help explain and quantify the physics of carrier trapping in staircase APD step regions. We show experimental electrical and optical data demonstrating carrier trapping to corroborate this model. Furthermore, we derive electrostatic parameters that should be considered when designing AlInAsSb staircase APDs with low-noise and deterministic gain scaling that mitigate the deleterious effects of carrier trapping and tunneling in the staircase step regions.