Near-infrared laser annealing of Ge layers epitaxially grown on Si for high-performance photonic devices

Abstract

Near-infrared laser annealing of Ge epitaxial layers on Si is studied as a postgrowth annealing process to reduce the density of threading dislocations (TDs) in Ge. Laser annealing is performed using an exposure of 1.07-μm-laser light with the power density as large as 8 kW/cm2 and the duration as short as 10 ms. The TD density is successfully reduced from 6 × 108 to 2 × 108 cm−2 in a 600-nm-thick Ge layer grown by ultrahigh-vacuum chemical vapor deposition on Si. Vertical pin photodetectors of laser-annealed Ge show a significant reduction of dark leakage current as small as 20 mA/cm2 with a high photodetection efficiency. The short annealing time is effective to prevent the dopant diffusion in Ge together with the Ge-Si intermixing at the interface, being applicable to the annealing even after the formation of pin junctions in Ge. In terms of the reduction of thermal budget, the use of longer wavelength up to ∼1.6 μm has potential applications to preferential annealing of Ge layers on a Si platform due to the strong optical absorption in Ge despite the high optical transparency in Si.