Precise Layer Control and Electronic State Modulation of a Transition Metal Dichalcogenide via Phase-Transition-Induced Growth.

Abstract

Wafer-scale growth of transition metal dichalcogenides with precise control over the number of layers, and hence the electronic state is an essential technology for expanding the practical application of 2D materials. Herein, a new growth method, phase-transition-induced growth (PTG), is proposed for the precisely controlled growth of molybdenum disulfide (MoS₂ ) films consisting of one to eleven layers with spatial uniformity on a 2 in. wafer. In this method, an energetically unstable amorphous MoS_x O_y (a-MoS_x O_y ) phase is effectively converted to a thermodynamically stable crystalline MoS₂ film. The number of MoS₂ layers is readily controlled layer-by-layer by controlling the amount of Mo atoms in a-MoS_x O_y , which is also applicable for the growth of heteroatom-inserted MoS₂ . The electronic states of intrinsic and Nb-inserted MoS₂ with one and four layers grown by PTGare are analyzed based on their work functions. The work function of monolayer MoS₂ effectively increases with the substitution of Nb for Mo. As the number of layers increases to four, charge screening becomes weaker, dopant ionization becomes easier, and ultimately the work function increases further. Thus, better electronic state modulation is achieved in a thicker layer, and in this respect, PTG has the advantage of enabling precise control over the film thickness.