Setting up a Tunable-Wavelength Laser for Measuring Mid-Infrared Emission from InSb Quantum Dots

Small bandgap semiconductors, such as PbS, PbSe, and InSb, that are optically sensitive to near- and mid-infrared (IR) light can be used to increase the wavelength solar spectrum sensitivity of modern, multipartite photovoltaics. As with other semiconducting materials, small bandgap semiconductors can be formed into quantum dots or colloidal nanocrystals, thus enhancing both their absorptive cross-sections and emission efficiencies, which are crucial optoelectronic parameters. Critically, the large exciton radii of many small bandgap semiconductors allows researchers to control the semiconducting bandgap by altering the quantum dot diameter around or below the exciton radius ( 10 to 20 nm). Here, we discuss the design and construction of a setup to detect mid-IR (1.5 to 6 μm) photoluminescence (PL) using a tunable, visible excitation source. Using this system, we measure PL from 15 nm diameter InSb quantum dots produced using Sn-seeded growth and atomic layer deposition. Using CdSe and PbS colloidal quantum dots, the system is tested in the visible and near-IR regime. Current mid-IR measurements of InSb epitaxial quantum dots do not show evidence of PL. In addition to these results, future measurements of InSb epitaxial quantum dots using high-intensity visible and near-IR excitation will be discussed.