SPIQuE: Semiconductor Photonics with InP Quantum Emitters

We will combine the advantages of bespoke colloidal quantum dots, and the wafer-scale manufacture of integrated photonic chips to create a platform for studying optical processes in single dots and on chip generation of quantum light. Integrated photonic circuits offer a versatile toolbox for advanced quantum optics applications, such as quantum communications. This requires bright, deterministic and spectrally pure sources of quantum light (single photons). Quantum dots (QDs), Nobel Prize in Chemistry 2023, can provide single photons with the required characteristics and importantly can be engineered into integrated photonic devices. When a semiconductor QD absorbs energy, an electron is excited to a higher energy level, leaving a hole behind. This electron-hole pair, an exciton, is confined leading to discrete energy levels. When the electron can efficiently recombine with the hole, bright photons are released that have a specific wavelength proportional to the difference between the energy levels. This energy can be tuned during manufacturing by careful control of the size of the QD resulting in spectrally pure photon emission. As QDs are small, there is generally only one exciton at a time, and so QDs only emit single photons on demand (and so deterministically) – which allows their utility in quantum optics. Indium Phosphide (InP) QDs are a versatile platform, with emission wavelengths ranging from 450-700 nm, through tuning size and composition. Current manufacturing processes use randomly distributed self-assembled QDs which require waveguide devices to be subsequently built around the QD. This is time consuming, costly, and limits scalability. Solution based techniques provide an alternative manufacturing route, as they are typically fast, cheap, and scalable. This project will combine the strengths of solution processed QDs (Keele) with the chip processing skills of the Compound Semiconductor Manufacturing Hub for a Sustainable Future (Cardiff) to develop QD-based integrated photonic circuits in GaN and AlN materials systems. These nitride materials are transparent at the wavelength of the InP QDs, so can guide and manipulate light with low loss. Incorporation of QDs inside carefully-designed photonic circuits will allow for electrical operation via monolithically integrated InGaN LEDs, enhanced photon emission into single modes via the Purcell effect and advancement of these materials for low loss, high efficiency emission. The materials challenges in creating low-loss photonic circuits builds on expertise in Cardiff on semiconductor processing and etching, which is complemented by Keele’s expertise in synthesising InP QDs. This project, “SPIQuE: Semiconductor Photonics with InP Quantum Emitters”, will empower an innovative approach to advance the manufacture of InP based integrated photonics. It will combine solution processed QDs with scalable semiconductor processing to manufacture inexpensive and accessible single quantum emitters for quantum devices and exploit a major gap in a critical market. In this project we will develop materials that offer route to functional, efficient integrated photonic circuits which can be mass-manufactured at low cost. We will functionalise specific points on these circuits so that we can add our separately prepared QDs in carefully selected locations through simple techniques that can easily be built into large scale manufacturing processes. In doing so, this research ties into the UK government’s National Semiconductor and Quantum Strategies, which aims to develop the UK as a world leader in these technologies. We wanted to play up the “advanced materials” angle of the scheme, which I think is important