Photonic-Crystal-Enhanced Single-Photon Sources Based on Semiconductor Quantum Dots

Quantum-dot single-photon sources are one of the key components for scal- able quantum photonic technologies. Photonic crystals provide a powerful and versatile platform for enhancing their performance. This review summa- rizes recent advances in tailoring the local optical density of states around quantum dots using photonic crystals, enabling efficient control of spon- taneous emission dynamics and emission directionality. We focus on four representative photonic-crystal platforms: Point-defect cavities, slow-light waveguides, topological cavities, and moiré flatband cavities. These plat- forms can be broadly understood within a unified physical framework based on two complementary mechanisms: mode localization induced by local sym- metry breaking, and enhancement arising from global band-structure engi- neering. We highlight their distinct enhancement mechanisms arising from their underlying band-structure properties, including localized defect modes, slow-light-induced density-of-states enhancement, symmetry-protected topo- logical edge and corner states, and mode localization in moiré lattices fea- turing ultra-flat bands. Together, these photonic-crystal platforms illustrate how diverse band-structure engineering strategies enable tunable emission enhancement, high-efficiency photon extraction, and pathways toward scal- able on-chip quantum photonic circuits. Continued advances across these platforms are expected to deepen our understanding of light–matter interac- tions and ultimately realize near-ideal solid-state on-demand single-photon sources