Simple, very low dark current, planar long-wavelength avalanche photodiode

We have demonstrated a novel planar, avalanche photodiode (APD) for use in long-wavelength (0.95–1.65 μm) optical communication systems. The device is a separate absorption and multiplication region APD utilizing p+ guard rings which are concentric with, but not attached to the central diffused p+-n junction region. Since no contact is made to the rings, their potential is allowed to ‘‘float’’ at a value somewhat less than that established by the externally applied voltage. The APD, which is fabricated in a manner identical to simple p-i-n photodiodes, eliminates edge breakdown effects while greatly reducing the electric field at the insulator/semiconductor interface. A 60-μm-diam junction device grown by vapor phase epitaxy is observed to have a primary dark current of <300 pA, and a capacitance of 290 fF at 90% of the breakdown voltage. Uniform gains as high as 11 have been observed.