Semiconductor nanopyramids for building high-yield quantum photonic devices

Abstract

Novel structures exhibit highly directional emission and provide a template for site-controlled quantum dots and self-aligned nanophotonic cavities. Semiconductor quantum dots (QDs) are thought to be a promising candidate for a single-quantum emitter in on-chip systems because of their well-developed growth and fabrication techniques. 1 Semiconductor QDs, however, have a number of inherent limitations that need to be overcome before they can be used in practical applications. For example, QDs in semiconductors are strongly affected by elements (e.g., phonons) in the surrounding environment, which results in short nonradiative decay times and rapid dephasing processes. Despite the high intrinsic radiative decay rates of semiconductor QDs compared with those of other single-quantum emitters (such as atoms and ions), the radiative decay rate needs to be further increased so that these fast nonradiative and dephasing processes can be overcome. Furthermore, the collection efficiency of the light that is emitted from conventional QDs embedded in a highindex planar substrate is typically low (about 4%). Processes with which to control and optimize the radiative decay rate of QDs are therefore crucial for increasing their collection efficiency and for realizing efficient single-photon generation. Indeed, improving the collection efficiency would be incredibly useful for the successful application of QDs in quantum information devices. Over the past few decades extensive efforts have been made to try and realize highly efficient light sources from single QDs, i.e., by introducing various photonics structures. 2 A critical problem arises, however, when photonics structures are combined with semiconductor QDs. That is, conventional semiconductor QDs become randomly distributed across the wafer and have nonreproducible sites. Moreover, these QDs have a broad spectral distribution. Achieving spectral overlap between a QD and a