InP/InGaAsP/InGaAs SAGM avalanche photodiode with delta-doped multiplication region

Gain-bandwidth products as high as 86 GHz have been reported for SAGM (separate absorption, grading, and multiplication) avalanche photodiodes. However, higher performance has been severely limited by very tight design constraints emanating from fundamental material properties. Smaller multiplication widths, needed to increase the gain-bandwidth product, have been difficult to implement due to the maximum doping limit in InP brought on by the onset of tunnelling. Fabrication of a novel SAGM APD is reported, in which the placement of change in the avalanche region is controlled through delta doping. The advantage of this approach results from the ensuing decoupling of the doping and thickness requirements of the avalanche region. Low dark currents and gain-bandwidth products of over 75 GHz have been obtained. In addition, by incorporating a surface reflector, a high quantum efficiency of 67% has been obtained with an absorption region only 1.1 mu m thick.