Design optimization of tensile-strained SiGeSn/GeSn quantum wells at room temperature

Abstract

A direct bandgap can be engineered in Ge-rich group-IV alloys by increasing Sn content and by introducing tensile strain in GeSn. Here, we combine these two routes in quantum well (QW) structures and systematically analyze the properties of SiGeSn/GeSn quantum wells for a range of Sn content, strain, and well width values, within realistic boundaries. Using the k Á p method, and including L-valley within the effective mass method, we find that 13-16 nm is a preferred range of well widths to achieve high gain for tensile-strained SiGeSn/GeSn quantum wells. Within the range of the well widths, a loss ridge caused by inter-valence band absorption and free carrier absorption is found in the region of parameter space where Sn content and strain in the well are related as Sn(%) % À7:71ε xx (%) þ 17:13. Limited by a practical strain boundary of 1.7%, for a 14 nm quantum well, we find that 7:5 + 1% Sn and 1 + 0:2% strain is a promising combination to get a good net gain for photon transition energy higher than ∼0.42 eV. A maximum utilization of strain is preferred to obtain the best gain with lower energies (<0.42 eV). By comparing these designs with a compressive strain example, an engineered tensile structure shows a better performance, with a low threshold current density (1.42 kA/cm 2 ). Finally, the potential benefit of p-doping of the tensile-strained GeSn QW is also discussed.

Lattice matched GeSn/InAlAs heterostructure: role of Sn in energy band alignment, atomic layer diffusion and photoluminescence

“…[1][2][3][4][5][6][7][8][9][10][11][12] Composition of Sn for this transition is stated over a range, since the bowing parameter of Ge 1Ày Sn y in the computation of energy bandgap varies between experimental and first-principles calculations. 21 Additionally, Ge 1Ày Sn y material has inherent advantages, such as: (i) increased direct band transitions of the carriers between conduction and valence bands, improving optical absorption to provide high photodetector responsivities; [22][23][24] (ii) lower effective mass (m eff ) of carriers in the G-valley than L-valley enhances mobility -thereby boosting the ON-current in a low power transistor; 25,26 (iii) compatibility with Si CMOS technology; [27][28][29][30] (iv) high carrier lifetime due to reduced surface roughness 31 by mitigating surface states induced recombination. Hence, a virtually defect-free lattice matched GeSn/InAlAs (or InGaAs) heterostructure is necessary to make better use of Ge 1Ày Sn y material in photonic integrated circuits (PICs) and optoelectronic applications.…”