Growth process-driven modulation of electrical characteristics in MBE-grown few-layer MoTe2

Abstract

2D TMDC materials are potential materials for future energy-efficient electronic and optoelectronic devices due to their clean, dangling-bond-free interface and interesting material properties. Controlling carrier statistics and the electrical properties is a crucial aspect for their wide application in ultrathin semiconductor-based devices; however, such tuning mostly requires extrinsic doping and bias operations. Here, we present our study on controlling the electrical properties of few-layer MoTe₂ films grown over a large area on sapphire using molecular beam epitaxy. The MBE growth parameters, such as growth temperature and chalcogen-to-metal flux ratio, have been optimized to control the stoichiometry of few-layer MoTe₂ films precisely. These stoichiometric changes, in turn, influence the electrical properties of the grown films. Raman spectroscopy and AFM were utilized to confirm the phase purity and uniformity of these films. The detailed XPS investigations show the effect of chalcogen deficiency (i.e., the presence of Te vacancies) and excess tellurium atoms on the semiconducting nature of the grown films. The significant shift in the fermi level towards the valence band confirms that the film becomes more p-type due to the presence of extra Te atoms in the lattice. Similarly, the presence of Te vacancies is found to shift the fermi level in the other direction. Our work provides a convenient approach for controlling MoTe₂'s electrical characteristics uniformly without introducing any foreign impurity. This effective control over the electrical nature of the grown films by modulating the growth parameters can be advantageous for utilizing the ambipolar nature (i.e., both n and p type nature) of 2D MoTe₂ for applications requiring transitions between electron and hole conduction.