LISA Pre - Phase A Report

Avalanche photodiodes include a substrate of a high resistivity material having at least a first surface. The substrate is of a particular conductivity type. In the substrate and at the first surface are a plurality of spaced apart regions of the same conductivity type as the substrate and defining the individual photodiode elements of the avalanche photodiode. Occupying the area at the first surface of the substrate not occupied by the spaced regions and extending into the substrate is a discontinuous layer of the same conductivity type as the spaced regions but of a conductivity concentration much lower than the conductivity concentration of the spaced regions. On the first surface of the substrate covering the discontinuous layer and slightly overlapping the spaced regions is a patterned passivation layer. The improvement of the present invention over the prior art is the addition of the discontinuous layer which reduces the electrical noise in the output signal of the avalanche photodiode.