Heteroepitaxial growth of high optical quality, wafer-scale van der\n Waals heterostrucutres

Abstract

Transition metal dichalcogenides (TMDs) are materials that can exhibit\nintriguing optical properties like a change of the bandgap from indirect to\ndirect when being thinned down to a monolayer. Well-resolved narrow excitonic\nresonances can be observed for such monolayers, however only for materials of\nsufficient crystalline quality, so far mostly available in the form of\nmicrometer-sized flakes. A further significant improvement of optical and\nelectrical properties can be achieved by transferring the TMD on hexagonal\nboron nitride (hBN). To exploit the full potential of TMDs in future\napplications, epitaxial techniques have to be developed that not only allow to\ngrowlarge-scale, high-quality TMD monolayers, but allow to perform the growth\ndirectly on large-scale epitaxial hBN. In this work we address this problem and\ndemonstrate that MoSe2 of high optical quality can be directly grown on\nepitaxial hBN on an entire two-inch wafer. We developed a combined growth theme\nfor which hBN is first synthesized at high temperature by Metal Organic Vapor\nPhase Epitaxy (MOVPE) and as a second step MoSe2 is deposited on top by\nMolecular Beam Epitaxy (MBE) at much lower temperatures. We show that this\nstructure exhibits excellent optical properties, manifested by narrow excitonic\nlines in the photoluminescence spectra. Moreover, the material is homogeneous\non the area of the whole two-inch wafer, with only +/-0.14 meV deviation of\nexcitonic energy. Our mixed growth technique may guide the way for future\nlarge-scale production of high quality TMD/hBN heterostructures.\n