RESUMEN
Van der Waals heterostructures open up vast possibilities for applications in optoelectronics, especially since it was recognized that the optical properties of transition-metal dichalcogenides (TMDC) can be enhanced by adjacent hBN layers. However, although many micrometer-sized structures have been fabricated, the bottleneck for applications remains the lack of large-area structures with electrically tunable photoluminescence emission. In this study, we demonstrate the electrical charge carrier tuning for large-area epitaxial MoSe2 grown directly on epitaxial hBN. The structure is produced in a multistep procedure involving Metalorganic Vapor Phase Epitaxy (MOVPE) growth of large-area hBN, a wet transfer of hBN onto a SiO2/Si substrate, and the subsequent Molecular Beam Epitaxy (MBE) growth of monolayer MoSe2. The electrically induced change of the carrier concentration is deduced from the evolution of well-resolved charged and neutral exciton intensities. Our findings show that it is feasible to grow large-area, electrically addressable, high-optical-quality van der Waals heterostructures.
RESUMEN
Transition metal dichalcogenides (TMDs) are materials that can exhibit intriguing optical properties like a change of the bandgap from indirect to direct when being thinned down to a monolayer. Well-resolved narrow excitonic resonances can be observed for such monolayers although only for materials of sufficient crystalline quality and so far mostly available in the form of micrometer-sized flakes. A further significant improvement of optical and electrical properties can be achieved by transferring the TMD on hexagonal boron nitride (hBN). To exploit the full potential of TMDs in future applications, epitaxial techniques have to be developed that not only allow the growth of large-scale, high-quality TMD monolayers but also allow the growth to be performed directly on large-scale epitaxial hBN. In this work, we address this problem and demonstrate that MoSe2 of high optical quality can be directly grown on epitaxial hBN on an entire 2 in. wafer. We developed a combined growth theme for which hBN is first synthesized at high temperature by metal organic vapor phase epitaxy (MOVPE) and as a second step MoSe2 is deposited on top by molecular beam epitaxy (MBE) at much lower temperatures. We show that this structure exhibits excellent optical properties, manifested by narrow excitonic lines in the photoluminescence spectra. Moreover, the material is homogeneous on the area of the whole 2 in. wafer with only ±0.14 meV deviation of excitonic energy. Our mixed growth technique may guide the way for future large-scale production of high quality TMD/hBN heterostructures.