Lattice Matched Tunable Wavelength GeSn Quantum Well Laser Architecture: Theoretical Investigation

In this work, we propose aninitial framework and present numerical estimates for designing a GeSn-based quantum well (QW) laser that can attain efficient lasing, while utilizing a monolithic lattice matched (LM) InGaAs/GeSn/InGaAs stack. GeSn QW emission characteristics depend significantly on the quantized energy level as the bulk bandgap reduces and approaches zero for high Sn. One factor that diminishes the quantum efficiency of light sources is the defects present within the active region, which result in non-radiative recombination. Furthermore, defects at the interface can hinder the band alignment causing loss of carrier confinement. InGaAs, InAlAs and a well-designed LGB can provide large band offsets with GeSn to form a type I separate confinement heterostructure (SCH) QW laser structure while enabling a virtually defect-free active region suitable for room temperature operation and scalable to an arbitrary number of QWs. When LM, the InAlAs and InGaAs layers provide a large total band offset of ∼1.1eV and ∼0.6eV, respectively. For a 10 nm GeSn QW SCH laser, a threshold current (J_TH) of ∼10 A/cm² can be achieved at an emission wavelength of ∼2.6 μm with a net material and modal gain of ∼3000 cm⁻¹ and ∼40 cm⁻¹, respectively. The J_TH and net gain can be optimized for the InAlAs/InGaAs/GeSn/InGaAs/InAlAs SCH laser structure for Sn between 8--18% by adaptively designing the SCH waveguide and QW. Through adaptive waveguide design, quantization, and Sn alloying, a wide application space (1.2 μm to 6 μm) can be covered.