Low Noise Avalanche Photodiodes Incorporating a 40 nm AlAsSb Avalanche Region

A separate absorption and multiplication avalanche photodiode incorporating a 500 nm InGaAs absorption layer, InAlAs bandgap grading/field control layers, an AlAsSb field control layer and a 40 nm AlAsSb multiplication layer was grown and characterized. Responsivity of 436 mA/W was measured at the punch-through voltage. A deviation of Be doping concentration in our AlAsSb field control layer leads higher than intended electric fields in the InGaAs absorption layer and the InAlAs field control layer. Calculation of avalanche gain suggests that the gain in the InGaAs is low and therefore the gain and excess noise characteristics are dominated by impact ionization in the InAlAs field control layer and the AlAsSb multiplication layer. Despite this low excess noise factors corresponding to an effective electron to hole ionization coefficient ratio between 0.1 to 0.15, were measured. This is lower than that from an InAlAs pin diode with a 100 nm avalanche region.