Nevertheless, reported N-doped graphene typically has broad distribution of thicknesses, high-density of grain boundaries, and variations over dopant concentration and distribution. Recently, N-doped graphene was successfully synthesized by mixing nitrogen compounds into forming gas during CVD growth 15, 16, 17. Production of graphene via CVD growth on transition metal substrates has been steadily maturing 13, 14. In contrast, substitutional doping with heteroatoms via chemical vapour deposition (CVD) provides an effective route for simple and stable tuning of doping levels in graphene. However, existing methods for fabrication of graphene p–n junctions usually require external gate 10 or unstable adsorbed chemical dopants 12, which are inconvenient for practical applications. Introduction of p–n junctions to graphene would allow for novel phenomena including Klein tunneling 8, negative refractive index for Veselago lens 9 and even photoelectric conversion with a hot carrier-assisted photothermoelectric process 10, 11. Graphene, a single layer of hexagonal carbon framework with broadband photon absorption and extraordinary carrier mobility 1, is attractive to high-performance electronic and optoelectronic devices, such as transistors 2, 3, 4, 5, optical modulators 6 and photodetectors 7. This study provides a facile avenue for large-scale synthesis of single-crystalline graphene p–n junctions, allowing for batch fabrication and integration of high-efficiency optoelectronic and electronic devices within the atomically thin film. Efficient hot carrier-assisted photocurrent was generated by laser excitation at the junction under ambient conditions. The unchanged crystalline registry during modulation doping indicates the single-crystalline nature of p–n junctions. Mosaic graphene is produced in large-area monolayers with spatially modulated, stable and uniform doping, and shows considerably high room temperature carrier mobility of ~5,000 cm 2 V −1 s −1 in intrinsic portion and ~2,500 cm 2 V −1 s −1 in nitrogen-doped portion. Here we develop a well-controlled chemical vapour deposition process for direct growth of mosaic graphene. Device applications of graphene such as ultrafast transistors and photodetectors benefit from the combination of both high-quality p- and n-doped components prepared in a large-scale manner with spatial control and seamless connection.
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