High n-type Sb dopant activation in Ge-rich poly-Ge_1-xSn_x layers on SiO₂ using pulsed laser annealing in flowing water

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 Ge_1-xSn_x layers (x ≈ 0.02) on SiO₂. It is found that fully melting a Ge_1-xSn_x layer down to the Ge_1-xSn_x/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-Ge_1-xSn_x 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 Ge_1-xSn_x based devices fabricated on 3D integrated circuits as well as flexible substrates.