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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 μmϕ) 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.

The crystal growth of single-crystalline Si1−xSnx layers with various Sn contents and analytical comparisons of their fundamental physical properties are strongly desired for next-generation group-IV electronics. In the present study, Si1−xSnx layers with varying Sn contents (1%−40%) were grown on various substrates [(001)-oriented Si, Ge, or InP] by solid-phase epitaxy. Crystallographic and composition analyses indicated that the grown Si1−xSnx layers were nearly lattice-matched to the substrates. When grown on Si, Ge, and InP substrates, the substitutional Sn contents were ∼1%, ∼20%, and ∼40%, respectively. Hard X-ray photoelectron spectroscopy revealed a valence-band offset resulting from the Sn substitution. The offset exhibited an upward-bowing tendency when plotted against the Sn content. The Si0.78Sn0.22/n-type Ge junction displayed rectifying diode characteristics with the ideality factor of 1.2.

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