Selective epitaxial germanium on silicon-on-insulator high speed photodetectors using low-temperature ultrathin Si0.8Ge0.2 buffer

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Abstract
The authors report the performance of selective epitaxialGe ( 400 nm ) on Si-on-insulator p - i - n mesa-type normal incidence photodiodes using ∼ 14 nm low-temperature Si 0.8 Ge 0.2 buffer without cyclic annealing. At − 1 V , very low bulk dark current densities of 1.5 – 2 mA ∕ cm 2 were obtained indicating good material quality, and the peripheral surface leakage current densities were 14 – 19.5 μ A ∕ cm . For 28 μ m diameter round photodiode, the highest achieved external quantum efficiencies at − 5 V were 27%, 9%, and 2.9% for 850 nm , 1.3 μ m , and 1.56 μ m optical wavelengths, respectively. 15 × 15 μ m 2 square photodiode has 3 dB bandwidth ⩾ 15 GHz at − 1 V . Good performance was achieved without high-temperature annealing, suggesting easy integration of Ge ∕ Si photodiode unto existing complementary metal-oxide-semiconductor process.