Abstract: An avalanche photodiode (APD) structure, comprising an absorption layer comprising InGaAs, InGaAlAs, InGaAsP, or an InGaAs/GaAsSb type-II superlattice, an avalanche layer comprising AlGaAsSb, and a transition portion disposed between the absorption layer and the avalanche layer is disclosed. The transition portion comprises a first grading layer of InAlGaAs or InGaAsP and a first field control layer disposed between the first grading layer and the avalanche layer. The first field control layer has a bandgap between the bandgap of the absorption layer and the bandgap of the avalanche layer. In an alternative embodiment, an avalanche photodiode (APD) structure, comprising an absorption layer comprising GaAsSb, an avalanche layer comprising AlGaAsSb, and a transition portion disposed between the absorption layer and the avalanche layer. The transition portion comprises a first grading layer and one or more field control layers having a bandgap between the bandgaps of the absorption layer and the avalanche layer.