Integrated quantum photonics relies critically on photon sources that have great purity, single-mode property, scalability, integrability and flexibility for both integrated quantum computing and long-haul quantum communication. Here we report a photon-pair/single-photon source that utilizes cavity-enhanced four-wave mixing in a high-Q silicon microresonator. The photon-pair source has a spectral brightness of 6:25 × 10<sup>8</sup> pairs/s/mW<sup>2</sup>/GHz and a quantum cross-correlation of g<sup>(2)</sup><sub>si</sub> (0) = (2:58 ± 0:16) × 10<sup>4</sup>. The generated photons are single-mode, with a quantum self-correlation of 1:87 ± 0:05. The heralded single photons has conditional photon autocorrelation g<sub>c</sub><sup>(2)</sup> as low as 0:0075 ± 0:0017 at 5:9 × 10<sup>4</sup> pair/s.
We propose and demonstrate a unique suspended slot-waveguide structure supported by a thin slab to realize
high-quality air-clad silicon slotted microring resonators (SMRs) on the silicon-on-insulator platform, based on a
fabrication process consisting of two-step electron beam lithography and inductively-coupled-plasma reactive-ion-
etching. Our SMRs can achieve an intrinsic optical quality factor (Q) above 10<sup>5</sup> operating at the telecom band,
which is the highest value for silicon SMRs reported to date. The demonstrated high-quality air-clad silicon SMRs
enable great potential for broad applications in biosensing, nonlinear photonics, and cavity optomechanics.