Hexagonal boron nitride (h-BN) has emerged as a promising platform for generating room temperature single photons exhibiting high brightness and spin-photon entanglement. However, improving emitter purity, stability, and scalability remains a challenge for quantum technologies. Here, we demonstrate highly pure and stable single-photon emitters (SPEs) in h-BN by directly growing carbon-doped, centimeter-scale h-BN thin films using the pulsed laser deposition (PLD) method. These SPEs exhibit room temperature operation with polarized emission, achieving a g ⁽²⁾ (0) value of 0.015, which is among the lowest reported for room temperature SPEs and the lowest achieved for h-BN SPEs. It also exhibits high brightness (~0.5 million counts per second), remarkable stability during continuous operation (>15 min), and a Debye-Waller factor of 45%. First-principles calculations reveal unique carbon defects responsible for these properties, enabled by PLD’s low-temperature synthesis and in situ doping. Our results demonstrate an effective method for large-scale production of high-purity, stable SPEs in h-BN, enabling robust quantum optical sources for various quantum applications.

Phase stability of boron nitride (BN) polymorphs at elevated temperature is perplexing due to their complex nucleation and growth kinetics, nevertheless, holds great significance in fundamental science and technology. Therefore, the phase-transformation of three-dimensional cubic BN (3D c-BN) to a two-dimensional hexagonal BN (2D h-BN) or vice versa, remains an exciting domain to explore. Here, we used temperature-dependent spark plasma sintering on 3D c-BN, enabling phase transformations to a mixed phase of 3D/2D c-BN/h-BN material and ultimately to 2D h-BN. The phase transformed 2D h-BN ceramic features an extremely high density reaching ∼90% of the theoretical limit, and exhibits excellent room temperature thermal conductivity and mechanical properties. Our findings provide valuable fundamental insights into the complex phase diagram, the relative stability regimes and boundaries of 3D c-BN and 2D h-BN phase, with the exhibition of functional properties, pivotal for extreme environments sustainable material-based technology.

The distinguished properties of hexagonal boron nitride (h-BN), specifically its atomically smooth surface, large critical electric field, and large electronic bandgap, make it ideal for thin film microelectronics and as an ultrawide bandgap semiconductor. Owing to weak van der Waals interactions between layers, h-BN exhibits a significant degree of anisotropic thermal conductivity. The in-plane thermal conductivity of h-BN has extensively been studied, yet the only measured data of cross-plane thermal conductivity (k⊥) are for exfoliated h-BN films. Exfoliation from bulk crystals is not a sustainable method for scalable production of h-BN due to its low repeatability, low yield, poor control of sample thickness, and limitation to small areas. Thus, it is necessary to investigate the thickness-dependence of k⊥ for thin films grown by a practical growth method, such as pulsed laser deposition (PLD), which enables the production of reliable and large-area h-BN films with a control of film thickness. We grew h-BN using PLD at 750 °C and observed a decreasing trend of k⊥ as thickness increases from 30 to 300 nm, varying from ∼1.5 to ∼0.2 W/(m K). We observed a relatively high k⊥ value for h-BN at a thickness of 30 nm, providing insight into the k⊥ of PLD-grown films suitable for electronics applications.