Effective concentration ratio driven phase engineering of MBE-grown few-layer MoTe2

Abstract

The polymorphic nature of ultrathin transition metal dichalcogenide (TMDC) materials makes the phase engineering of these materials an interesting field of investigation. Understanding the phase-controlling behavior of different growth parameters is crucial for obtaining large-area growth of a desirable phase. Here, we report a detailed study on the effect of growth parameters for engineering different phases of few-layer MoTe₂ on sapphire using molecular beam epitaxy (MBE). Our study shows that the 2H phase of MoTe₂ is stabilized in a certain regime of the flux ratio and growth temperature, while on both the lower, as well as, the higher sides of this regime, the 1T′ phase is favored. The combined effect of growth parameters is explained using the effective concentration ratio of Te and Mo at the growth surface, which is found to be the primary factor governing the phase selectivity in few-layer MoTe₂. XPS and KPFM investigations show the contribution of excess carrier doping in driving the phase change. The effect of the sapphire substrate on the crystallinity and phase-dependent morphological features has also been studied. This knowledge of versatile and controlled phase engineering of few-layer MoTe₂ paves the way for fabricating large-scale hetero-phase-based metal–semiconductor heterostructures for future electronic and optoelectronic device applications.