Hyperdoping of germanium with argon toward strain-doping-induced indirect-to-direct bandgap transition in Ge.

This article focuses on experimentally demonstrating the strain-doping concept in germanium (Ge) to induce an indirect-to-direct bandgap transition by implanting argon (Ar) ions and recrystallizing the damaged layer. The study compares nanosecond laser annealing (NLA) and furnace thermal annealing (FTA) for recrystallizing Ar-doped amorphous Ge, finding that NLA effectively restores crystal quality while retaining a critical Ar concentration (0.8%) necessary for bandgap transition, unlike FTA which results in significant Ar loss and poorer recrystallization. Although the resulting Ar-enriched Ge layer is only about 3.8 nm thick—too thin to isolate photoluminescence signals from the substrate—the work establishes a foundation for future optimization through increased implantation energy, capping layers, or heterostructure substrates to realize CMOS-compatible on-chip light emitters based on strain-doped Ge.