Heavy n-type doping in polycrystalline Ge (poly-Ge) is still under development owing to the low solid solubility and the low activation ratio of group-V dopants in Ge. To solve this problem, we have investigated ultra-short (55 ns) laser pulse annealing in flowing water for Sb-doped amorphous Ge1-xSnx layers (x ≈ 0.02) on SiO2. It is found that fully melting a Ge1-xSnx layer down to the Ge1-xSnx/SiO2 interface leads to a large grained (∼0.8 μmη) growth, resulting in not only a high electrical activation ratio (∼60%) of Sb atoms in the polycrystals but also a high electron density around 1020 cm-3. As a result, the electron mobility in the Ge-rich poly-Ge1-xSnx layers exceeds that in single-crystalline Si even in the region of a high electron density around 1020 cm-3. The low thermal budget process opens up the possibility for developing Ge1-xSnx based devices fabricated on 3D integrated circuits as well as flexible substrates.
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