Anthony. J. Bennett

Gallium nitride (GaN) quantum emitters (QEs) have rapidly emerged as a promising platform for room-temperature single-photon generation, benefiting from high emission rates, robust optical properties, and compatibility with industrial GaN epitaxy and device fabrication. Over the past decade, these emitters have demonstrated bright, linearly polarized emission, strong antibunching without tight spectral filtering, and in some cases microwave and magnetically addressable spin transitions, highlighting their potential for quantum communication, sensing, and integrated photonics. In this Perspective, we consolidate recent progress in understanding the formation, control, and photophysical behaviour of GaN QEs, including advances in controlled epitaxy, activation techniques, and external-field tuning. We further discuss outstanding questions surrounding their microscopic origin and spectral variability, and identify key challenges related to spectral stability, spin coherence, and device integration. Finally, we outline the most promising research directions and technological pathways that could enable scalable, low-cost, room-temperature quantum light sources based on GaN.

Mixing the fields generated by different light sources has emerged as a powerful approach for engineering non-Gaussian quantum states. Understanding and controlling the resulting photon statistics is useful for emerging quantum technologies that are underpinned by interference. In this work, we investigate intensity correlation functions arising from the interference of resonance fluorescence from a quantum emitter with a coherent laser field. We show that the observed bunching behavior results from a subtle interplay between quantum interference and the normalization of the correlation functions. We show that by adjusting the mixing ratio and phase, one can achieve full tunability of the second-order correlation, ranging from anti-bunching to bunching. We further extend our analysis to third-order correlation functions, both experimentally and theoretically, to provide new insights into the interpretation of higher-order correlations and offer practical tools for shaping quantum optical fields.

Photonic integrated circuit sensors can be used for precise sensing of the environment, offering the advantage of integration with fiber networks for remote and multiplexed sensor arrays. In this work, we examine the performance of aluminum nitride on sapphire microdisk mode resonators in an all-pass configuration. We discuss their potential as on-chip temperature sensors under fixed-frequency and frequency-scanning modes, demonstrating the latter can measure a 1 K temperature change with an uncertainty of ±5.1 mK over a temperature range of 25–55 °C.

Quantum emitters (QEs) in the solid state can be spatially aligned with nanostructures to increase the photon collection efficiency and radiative emission rate. In many promising material platforms, these QEs are randomly positioned over the sample area, necessitating precise mapping of the emitter location and subsequent agile lithography aligned with the source. We have developed a programmable confocal microscope system to localize QEs with subwavelength precision, and subsequently accurately define nanostructures around the emitters. We show that repeated sampling of emitter location relative to alignment markers can account for sample drift and localize the emitter position within a few tens of nanometers. We demonstrate the deterministic enhancement of the collected photon intensity by up to 84% for emitters embedded in a micropillar.

The ability to generate quantum light at room temperature on a mature semiconductor platform opens up new possibilities for quantum technologies. Heteroepitaxial growth of gallium nitride on silicon substrates offers the opportunity to leverage existing expertise and wafer-scale manufacturing to integrate bright quantum emitters in this material within cavities, diodes, and photonic circuits. Until now, it has only been possible to grow GaN QEs at uncontrolled depths on sapphire substrates, which is disadvantageous for potential device architectures. Here, we report a method to produce GaN QEs by metal-organic vapor phase epitaxy at a controlled depth in the crystal through the application of silane treatment and subsequent growth of 3D islands. We demonstrate this process on highly technologically relevant silicon substrates, producing room-temperature QEs with a high Debye Waller factor and strongly anti-bunched emission.

Controlling the photonic environment of emitters is essential to the design of classical and quantum light sources. We study the case of a dipole-like emitter in a cylindrical pillar etched into a planar Bragg microcavity, which is a common design of quantum-dot single photon source. In addition to the well-known cavity modes created by the high-reflectivity of the Bragg mirrors at small in-plane wavevectors, we show the presence of broad spectral features that play a key role in controlling photon collection efficiency and Purcell enhancement. These non-cavity modes are insensitive to the periodic index modulation of the Bragg reflectors, but arise from the cylindrical pillar geometry, as we show by comparison with simulations of uniform pillars, which reproduce the non-cavity modes. This approach provides a tool for understanding and modelling these often-disregarded decay channels as a function of source height, cavity dimensions and surface layers.

The ability to generate quantum light at room temperature on a mature semiconductor platform opens up new possibilities for quantum technologies. Heteroepitaxial growth of gallium nitride on silicon substrates offers the opportunity to leverage existing expertise and wafer-scale manufacturing to integrate bright quantum emitters (QEs) in this material within cavities, diodes, and photonic circuits. Until now, it has only been possible to grow GaN QEs at uncontrolled depths on sapphire substrates, which is disadvantageous for potential device architectures. Here, we report a method to produce GaN QEs by metal-organic vapor phase epitaxy at a controlled depth in the crystal through the application of silane treatment and subsequent growth of 3D islands. We demonstrate this process on highly technologically relevant silicon substrates, producing room-temperature QEs with a high Debye–Waller factor and strongly anti-bunched emission.

Controlling the photonic environment of emitters is essential to the design of classical and quantum light sources. We study the case of a dipole-like emitter in a cylindrical pillar etched into a planar Bragg microcavity, which is a common design of quantum-dot single photon source. In addition to the well-known cavity modes created by the high-reflectivity of the Bragg mirrors at small in-plane wavevectors, we show the presence of broad spectral features that play a key role in controlling photon collection efficiency and Purcell enhancement. These ‘non-cavity’ modes are insensitive to the periodic index modulation of the Bragg reflectors, but arise from the cylindrical pillar geometry, as we show by comparison with simulations of uniform pillars, which reproduce the non-cavity modes. This approach provides a tool for understanding and modelling these often-disregarded decay channels as a function of source height, cavity dimensions and surface layers.

Mixing the fields generated by different light sources has emerged as a powerful approach for engineering non-Gaussian quantum states. Understanding and controlling the resulting photon statistics is useful for emerging quantum technologies that are underpinned by interference. In this work, we investigate intensity correlation functions arising from the interference of resonance fluorescence from a quantum emitter with a coherent laser field. We show that the observed bunching behavior results from a subtle interplay between quantum interference and the normalization of the correlation functions. We show that by adjusting the mixing ratio and phase one can achieve full tunability of the second-order correlation, ranging from anti-bunching to bunching. We further extend our analysis to third-order correlation functions, both experimentally and theoretically, to provide new insights into the interpretation of higher-order correlations and offer practical tools for shaping quantum optical fields.

Femtosecond laser-writing offers distinct capabilities for fabrication, including three-dimensional, multimaterial, and sub-diffraction-limited patterning. In particular, demonstrations of laser-written quantum emitters and photonic devices with superior optical properties have attracted attention. Recently, gallium nitride (GaN) has been reported to host quantum emitters with narrow and bright zero-phonon photoluminescence from ultraviolet to telecom ranges. However, emitters formed during epitaxy are randomly positioned, and until now, it has not been possible to fabricate quantum emitters in ordered arrays. In this paper, we employ femtosecond laser writing to create nanoablations with sub-diffraction-limited diameter and use rapid thermal annealing to activate co-located stable emitters. The emitters show a MHz antibunched emission with a sharp spectral peak at room temperature. Our study not only presents an efficient approach to laser-written nanofabrication on GaN but also offers a promising pathway for the deterministic creation of quantum emitters in GaN, shedding light on the underlying mechanisms involved.