Solid-phase crystallization of densified amorphous GeSn leading to high hole mobility (540 cm2/V s)

Improving carrier mobility of polycrystalline Ge films by incorporating Sn is a topic recently attracting a great deal of attention. Here, we substantially update the maximum hole mobility of the polycrystalline GeSn film formed on insulators. In the solid-phase crystallization (SPC) of densified amorphous GeSn on glass, the initial Sn concentration xi (<0.05), film thickness t (40–200 nm), and growth temperature Tanneal (<500 °C) strongly influence the grain size and electrical properties of the resulting GeSn layer. The best characteristics are obtained for xi = 1.6%, which is the largest xi that allows Sn fully substituted in the SPC-GeSn. Reflecting the balance between grain boundary scattering, impurity scattering, and interfacial scattering, the hole mobility is maximized to 420 cm2/V s at t = 150 nm and Tanneal = 475 °C. Moreover, post annealing at 500 °C is effective in reducing defect-induced acceptors and then impurity scattering, especially for Tanneal = 375 °C. This results in a hole mobility ...