Shallow-junction p+-n germanium avalanche photodiodes (APD’s)

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Abstract
Low‐noise and high‐quantum‐efficiency germanium APD’s have been investigated by a p+‐n structure. Boron implantation was used to form the p+ layer. Shallow p+‐n junctions have a lower excess noise that n+‐p junctions because holes have a higher ionization coefficient in germanium, and these p+‐n diodes have a higher hole‐to‐electron collection efficiency. Excess noise factors F≈7 at a multiplication factor of 10 are obtained at wavelength of ∼1.4 μm, whereas F≈11 for n+‐p diodes. An internal quantum efficiency of ∼80% is obtained at 1.15 μm.