High-efficiency phosphorus activation in Ge0.95Sn0.05 enabled by ion implantation and flash lamp annealing with preserved alloy integrity

Heavy n-type doping is essential for GeSn-based optoelectronic and plasmonic devices, yet remains challenging due to the low thermal stability of GeSn alloys and the resulting dopant deactivation, strain relaxation, and Sn redistribution during post-growth processing. Here, we investigate phosphorus ion implantation combined with millisecond flash lamp annealing (FLA) as a non-equilibrium doping approach for Ge0.95Sn0.05 layers grown on Ge virtual substrates. Compared with previous ex-situ doping studies, the implantation process was redesigned using reduced implantation fluences, room-temperature implantation, an amorphous Si capping layer, and FLA without substrate preheating to improve dopant activation and minimize implantation-induced damage. Raman spectroscopy identifies a narrow recrystallization window between 71 and 84 J/cm2, while Rutherford backscattering spectrometry demonstrates nearly complete recovery of the crystalline quality after annealing, with a Sn lattice-site occupancy exceeding 95%. No measurable Sn redistribution is observed after implantation and annealing within the sensitivity limits of Rutherford backscattering spectrometry and X-ray diffraction. Hall-effect measurements reveal active electron concentrations of up to 5.0 × 10^19 cm-3 and electron mobilities of around 200 cm2 V-1 s-1. These results represent a 10% improvement in maximum carrier concentration and a ninefold increase in dopant activation efficiency compared to previously reported ex-situ doping approaches, reaching approximately 54%. These results establish an optimized processing route for highly activated n-type GeSn that suppresses Sn redistribution.