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Point defects in gallium nitride (GaN) have recently emerged as a promising platform for room-temperature single-photon generation, exhibiting high emission rates and robust optical properties. GaN also benefits from well-established fabrication processes due to its widespread use in applications such as solid-state lighting and high power and high frequency electronics. Whilst wafers of bulk GaN are increasingly widely available, the material is still most commonly grown heteroepitaxially, and the use of silicon substrates allows for production of up to 300 mm diameter wafers. Meanwhile, GaN single photon emitters offer linearly polarized emission, Debye–Waller factors of approximately 50%, and the possibility of microwave control of optically addressable spin states. Overall, the combination of a relatively mature materials system and promising single photon emitter properties offer real potential for the development of scalable quantum technologies based on GaN.
However, the nature of the single photon emitting defects in GaN is unknown, and it has proved difficult to control their density or location. Early studies suggested that the emitters might consist of a point defect residing inside or next to a stacking fault (SF) [1], but attempts to engineer structures with deliberately included SFs to promote emitter formation met with little success [2]. For nitrides grown on sapphire, evidence has accumulated that the majority of emitters form close to the nitride/sapphire interface [3]. This location does not facilitate the fabrication of devices containing emitters, since it renders it difficult to position doped layers or elements of optical cavities below the emitter in the epitaxial stack.
However, the insight that emitters may form in the highly defective region at the GaN/sapphire interface has inspired efforts to try and reproduce the relevant growth conditions at a more convenient location: part way through the epitaxial stack in GaN-on-silicon material [4]. Following growth of Al(Ga)N layers required to control strain in GaN-on-silicon, and the growth of an initial GaN buffer, the GaN surface was treated with silane (SiH4) and ammonia (NH3) for 720 s to form a thin layer of SiNx like that created during the initial nitridation step in GaN/sapphire growth. Thereafter a thin GaN layer was deposited at low temperature, and the sample was then annealed in ammonia at 1020 °C. This process resulted in the formation of a disordered array of GaN islands, the locations of which correlated with the locations of quantum emitters. A similar sample was capped with a further 3 µm of GaN, to increase the stability of quantum light emission by preventing reactions with air and surface charges. The capped structures contained defects which demonstrated bright single photon emission at room temperature, but which could be removed by etching away just over 3 µm of GaN, demonstrating that the emitters had formed at the intended depth. This is an important step towards control of quantum emitter locations in GaN-on-silicon.
[1] A.M. Berhane et al. Adv. Mater. 2017 29 1605092.
[2] M. Nguyen et al. APL Mater. 2019 7 081106.
[3] H.B.Yağcı, et al. Optical Materials 2024 156 115967.
[4] K.M.Eggleton et al. APL Photonics 2026 11 016103.