Sb surfactant-mediated SiGe graded layers for Ge photodiodes integrated on Si

High-quality SiGe and Ge thin films were grown on Si substrates by molecular-beam epitaxy using a technique that combines SiGe composition grading and Sb surfactant mediation. Both transmission electron microscopy and Schimmel defect etch measurements show that the Sb surfactant-mediated SiGe graded buffer layers have lower dislocation densities than those without an Sb surfactant. A systematic study of Sb surfactant-mediated graded buffers was carried out. The relationship between the threading dislocation densities and the grading rates of the Sb surfactant-mediated SiGe buffer layers was investigated. Moreover, p-i-n Ge photodiodes were fabricated on Si substrates using Sb surfactant-mediated SiGe graded buffer layers. These photodiodes exhibit very low dark current densities of about 0.15mA∕cm2 at the reverse bias of 1 V and high quantum efficiencies of 50%–72%.