Design of direct band gap type I GeSn/Ge quantum dots for mid-IR light emitters on Si substrate

This work reports on a theoretical study of the optimal size and composition of Ge1−xSnx quantum dots (QD) on buffered Ge on a Si substrate for direct band gap type I light emitters. The heavy holes and electron confined energy in Γ and L points are evaluated for strained ellipsoidal QD with different sizes and composition. An applicability criterion, involving carriers’ confinement, has been established for efficient use of this QD for light emitters. The lower dot size and composition limit is governed by the energy difference between the ground state electron in Γ and L points, and the upper limit by the energy spacing between the lowest confined energies at Γ-point being higher than thermal energy at room temperature. It is found that GeSn QD is potentially interesting for light emitters on Si substrate, covering an emission wavelength range between 2.7 and 3.5 μm and opening new perspectives in CMOS compatible QD based mid-IR optoelectronics.