Photocurrent analysis of a fast Ge p-i-n detector on Si

Germanium vertical $p\text{-}i\text{-}n$ photodetectors grown on silicon with molecular beam epitaxy are investigated. The photocurrent of a high speed detector structure is analyzed at infrared wavelengths of around $1.3\mu \mathrm{m}$ . The dark current and photocurrent were measured for reverse and forward biased detectors. It is clearly shown that the photocurrent is proportional to the width of the depletion layer. This means that the fast carriers from the depletion layer generate mainly the photocurrent and by this the high speed operation of the germanium detector is explained. Nearly abrupt junctions and low background doping allow zero bias operation of these detectors.