Ultrahigh-Quality Ge-on-Glass with a 3.7% Uniaxial Tensile Strain

While there have been notable advancements in the quality of epitaxial Ge on Si, the crystal quality of bulk Ge remains much superior, which provides an effective method to study the performance potentials of Ge-based semiconductor devices. This study showcases the development of ultrahigh-quality Ge/poly-Si/SiO₂ on glass with a Ge thickness reduced to ≤100 nm (10 μm width) through wafer bonding, thinning, and polishing processes. The minority lifetimes measured for the Ge thin films range between 200 and 1000 ns, surpassing those achieved with epi-Ge on Si by at least 20 to 100 times. The wafer bonding process introduces a desirable tensile strain of 0.1%, attributed to thermal expansion mismatch. A Ge microbridge structure was employed to amplify the tensile strain, reaching a maximum uniaxial tensile strain of 3.7%. The much longer minority carrier lifetime together with the strain-induced band gap engineering holds promise for improving light emission efficiency. This work establishes an economical and convenient method for producing high-quality tensile-strained Ge thin films, a pivotal step in exploring the potential of Ge in light emission applications.