Delta-doped avalanche photodiodes for high bit-rate lightwave receivers

Experimental results of a new avalanche photodiode (APD) structure in which a delta-doped layer has been placed on the multiplication region of an InP/InGaAsP/InGaAs avalanche photodiode are presented. The peak electric field in the multiplication layer is lowered and the thickness and doping limitations emanating from fundamental material and device design requirements are decoupled. Using conventional theory, it is proven that while the thinner multiplication regions possible in this structure lead to improved gain-bandwidth product performance, this is possible only with a concomitant increase in the multiplication noise. Fabrication of such a structure is reported. Low dark currents and high gain-bandwidth products exceeding 75 GHz have been obtained