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

Abstract

The authors report the performance of selective epitaxial Ge (400nm) on Si-on-insulator p-i-n mesa-type normal incidence photodiodes using ∼14nm low-temperature Si0.8Ge0.2 buffer without cyclic annealing. At −1V, very low bulk dark current densities of 1.5–2mA∕cm2 were obtained indicating good material quality, and the peripheral surface leakage current densities were 14–19.5μA∕cm. For 28μm diameter round photodiode, the highest achieved external quantum efficiencies at −5V were 27%, 9%, and 2.9% for 850nm, 1.3μm, and 1.56μm optical wavelengths, respectively. 15×15μm2 square photodiode has 3dB bandwidth ⩾15GHz at −1V. Good performance was achieved without high-temperature annealing, suggesting easy integration of Ge∕Si photodiode unto existing complementary metal-oxide-semiconductor process.