Silicon doping assisted phase transition of h-BN to c-BN via thermal annealing.

Heteroatom doping in hexagonal boron nitride (h-BN) films has been regarded as an effective solution to adjust their electrical and optical properties for realizing applications in various technologies. A high-temperature annealing process is routinely utilized to enhance the doping efficiency following film growth, which is, however, accompanied by other unexpected effects. Thus, understanding the dopant behavior induced by temperature is crucial for unlocking unprecedented development of h-BN. Here, we report the thermally induced mutual diffusion in Si-doped h-BN films grown on sapphire substrates, which can facilitate the transition from the hexagonal to the cubic phase. Spectral analysis indicates that as the annealing temperature increases, the doped films undergo a phase transition from hexagonal to cubic BN phases via an intermediate of explosive BN. Combined x-ray photoelectron spectroscopy and secondary ion mass spectrometry reveal that the thermal annealing above 1000 °C induces the interdiffusion of Si and Al through the interface, where the latter originates from the decomposition of the sapphire substrate. First-principles calculations reveal that the substitution of Si within BN reduces the energy barrier from sp2 to sp3 phase transformation by supplying electrons to adjacent N atoms. This work provides novel insights into understanding the doping behavior in h-BN films and the development of h-BN based devices.