Growth of p-doped 2D- Mo S 2 on A l 2 O 3 from spatial atomic layer deposition

In this letter, we report on the synthesis of monolayers of Mo S 2 via chemical vapor deposition directly on thin films of A l 2 O 3 grown by spatial atomic layer deposition. The synthesized monolayers are characterized by atomic force microscopy as well as confocal Raman and photoluminescence spectroscopies. Our data reveal that the morphology and properties of the 2D material differ strongly depending on its position on the substrate. Close to the material source, we find individual flakes with an edge length of several hundred microns exhibiting a tensile strain of 0.3 %, n-doping on the order of n e = 0.2 × 10¹³ cm⁻², and a dominant trion contribution to the photoluminescence signal. In contrast to this, we identify a mm-sized region downstream, that is made up from densely packed, small Mo S 2 crystallites with an edge length of several microns down to the nanometer regime and a coverage of more than 70 %. This nano-crystalline layer shows a significantly reduced strain of only <0.02 %, photoluminescence emission at an energy of 1.86 eV with a reduced trion contribution, and appears to be p-doped with a carrier density of n h = 0.1 × 10¹³ cm⁻². The unusual p-type doping achieved here in a standard chemical vapor deposition process without substitutional doping, post-processing, or the use of additional chemicals may prove useful for applications.