Phosphorus-incorporated layered carbon nitride films and their electronic and magnetic properties

Abstract

Layered carbon nitride (g-C₃N₄) is a semiconducting material that is used in electronic applications, and its physical and chemical properties can be improved by incorporating foreign atoms. We prepared highly ordered P-incorporated g-C₃N₄ crystalline films via chemical vapor deposition using powder sources and then studied their electronic and magnetic properties. The optical absorption edge shifted to the low-energy side with incorporation of increasing P content, which indicated a narrow energy bandgap. Analysis of the chemical bonding via X-ray photoelectron spectroscopy revealed that P atoms were incorporated into the nearest-neighbor C sites of the N atoms bridging the heptazine units. No significant degradation of crystallinity was observed when the substrate temperature was below 620 °C and P composition was below 10%. Furthermore, n-type conductivity was achieved because the P atoms incorporated into the C sites acted as donor impurities. A giant anisotropy of electron transport with a dependence on the crystal orientation was demonstrated, leading to low out-of-plane and high in-plane resistivities with anisotropy ratios above 4 × 10⁵. The activation energy for electron generation was estimated to be approximately 102.5 meV from the temperature dependence of resistivity. Notably, ferromagnetism without metallic elements was observed at room temperature. In addition, anisotropic ferromagnetism was observed along the out-of-plane and in-plane directions, which were large and small saturation magnetizations, respectively.