Tensile-strained InGaAs quantum dots with interband emission in the mid-infrared*

Tensile strain is an effective tool for III-V semiconductor band structure engineering, narrowing the band gap and pushing light emission toward the technologically relevant mid-infrared spectral range. The challenge is to create the large tensile strains needed without forming dislocations that destroy the material’s optoelectronic properties. Tensile-strained quantum dots (QDs) offer a solution. These defect-free nanostructures self-assemble on (111)-oriented surfaces under tensile strains ≥ 4%.

 

To pursue light emission in the 2–4 μm range, we targeted tensile In_0.5Ga_0.5As QDs grown on GaSb(111)A. Although bulk In_0.5Ga_0.5As emits light at ∼1.5 μm, the 4% tensile strain in the QDs permits access to longer wavelengths. The QDs form spontaneously during molecular beam epitaxy via the Volmer-Weber growth mode. We combine microscopic and spectroscopic characterization of the QDs with computational modeling. Simulations show In_0.5Ga_0.5As/GaSb QDs have an effective type-II band structure with electron confinement. Residual tensile strain in the QDs reduces the InGaAs band gap energy to produce band-to-band emission at 3.5–3.9 μm. When coupled with quantum size effects, the use of tensile strain to red-shift QD emission represents a route to novel, highly tunable mid-IR light sources.