An array of semiconductor-based microlaser cavities use quantum dots as their gain medium
An array of semiconductor-based microlaser cavities use quantum dots as their gain medium lead image
In a unique display of microarchitectural ingenuity, oxidized semiconductor sites serve a dual purpose in a method that produces an array of 10-micron micropillar cavities. The mesa-style sites serve as both a cavity’s aperture and the nucleation center during quantum dot (QD) growth, localizing and aligning no more than 10 QDs that can then act as the microcavity’s gain medium. In Applied Physics Letters, authors describe creating the patterned, multilayer stack from which they carve arrays of micropillars, each centered around a buried oxidized aluminium arsenide (AlAs) aperture and QD cluster.
QD manufacturing finds numerous ways to optimize optical quality precision, and it’s also starting to address industrial needs for reliability and scalability. Microresonators, often made via lithographic patterning, are therefore a natural match for QD development. There are two main approaches for placing QDs into (micro)resonators: aligning resonators around isolated QDs after self-assembly growth, or growing them inside prefabricated structures. Site-controlled QDs (SCQDs) are scalability-friendly, but typically result in lower quality light emission.
The authors realized, however, that if these buried-stressor sites took the form of an aperture, they would be aligned with the localized QDs after growth. Using lithography and dry etching, they created AlAs apertures on top of alternating layers of AlGaAs with differing amounts of aluminum that form the first reflector. Layer thicknesses determined the cavity dimensions needed to support the QD resonances, as well as place the aperture at an antinode of the electric field.
The method also demonstrated a reliable control over a given site’s number of QDs with the aperture size. Larger apertures led to more QDs. After oxidation, and growing the SCQDs and final reflector layers, e-beam lithography carved out the QD-embedded micropillar cavities. The final structures emit at around 930 nanometers with very high optical quality and impressive one-QD Purcell enhancement, increasing the emission rate factor by about four.
Source: “Micropillars with a controlled number of site-controlled quantum dots,” by Arsenty Kaganskiy, Fabian Gericke, Tobias Heuser, Tobias Heindel, Xavier Porte, and Stephan Reitzenstein, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5017692 .
