Highly n-doped, tensile-strained Ge grown on Si by molecular beam epitaxy

Highly n-doped, tensile-strained Ge is grown on Si substrate with a three-step method by solid source molecular beam epitaxy. Tensile strain of 0.22% is obtained in the Ge film due to the thermal expansion mismatch between Si and Ge. Activated n-type doping concentration of 5.0 × 10¹⁸ cm⁻³ is also realized by Sb in-situ doping during epitaxy and post-growth annealing. Strong photoluminescence (PL) is observed around 1.5–1.6 μm from direct band gap transition of Ge at room-temperature. Starting from this material, free-standing microdisks are fabricated by electron beam lithography, dry etching of Ge and subsequent Si undercutting. Significantly enhanced light emission and sharp resonant peaks with Q-factor approaching 800, are observed in the PL spectra. - Highlights: • Highly n-doped (5 × 10¹⁸ cm⁻³) Ge with tensile strain of 0.22% was grown on Si. • Direct band photoluminescence was 3.4 times enhanced compared with that of bulk Ge. • Ge microdisk showed largely enhanced emission and sharp resonant peak (Q ∼ 800)