Efficient In Situ Doping of Strained Germanium Tin Epilayers at Unusually Low Temperature

Efficient p‐ and n‐type in situ doping of compressively strained germanium tin (Ge 1‐x Sn x ) semiconductor epilayers, grown by chemical vapor deposition on a standard Si(001) substrate, is demonstrated. Materials characterization results reveal unusual impact of dopants manifesting via a pronounced reduction of Sn content in the epilayer, accompanied by an enhancement of the growth rate, due to increasing p‐type doping concentration. Furthermore, the opposite behavior for n‐type doping is observed, resulting in a less pronounced increase of Sn concentration and no effect on growth rate. Nevertheless, a very high density of electrically active holes up to ≈4 × 10 20 cm −3 is obtained in p‐type doped Ge 1‐x Sn x epilayer resulting in the lowest resistivity of 0.15 mΩ cm among all in situ doped epitaxial and strained group‐IV semiconductors. Also, the metal‐to‐insulator transition in Ge 1‐x Sn x is experimentally demonstrated for doping levels above 1 × 10 17 cm −3 , which is substantially lower than in any group‐IV semiconductor, and theoretically predict it to be as low as ≈1 × 10 17 cm −3 . The findings enabled by the doping regime explored in this work can open novel prospects to engineer low resistivity contacts and charge current injection in applications covering next‐generation transistors, qubits, diodes, electrically driven light sources, sensors and hybrid quantum devices.