Few-Layer WS₂–WSe₂ Lateral Heterostructures: Influence of the Gas Precursor Selenium/Tungsten Ratio on the Number of Layers

Abstract

Two-dimensional (2D) lateral heterostructures based on transition metal dichalcogenides (TMDCs) attract great interest due to their properties and potential applications in electronics and optoelectronics, such as p–n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, the studies of 2D lateral heterostructures have mainly focused on monolayer nanosheets despite bilayer heterostructures exhibiting higher performance in many electronic and optoelectronic devices. It remains a great challenge to synthesize lateral heterostructures with few layers. Here, we report the growth of bilayer–bilayer (bl–bl), bilayer–bilayer–monolayer (bl–bl–mo), bilayer–monolayer (bl–mo), monolayer–bilayer (mo–bl), and monolayer–monolayer (mo–mo) tungsten disulfide (WS2) and tungsten diselenide (WSe2) lateral heterostructures. The selenium/tungsten (Se/W) ratio of WSe2 precursor powders and the growth atmosphere can be changed with the extension of annealing time, which influences the layer number of the heterostructures. More bilayer WSe2 epitaxially grows at the WS2 edge with short annealing time (high Se/W ratio), and more monolayer WSe2 grows at the WS2 edge with long annealing time (low Se/W ratio). The density functional theory (DFT) calculations provide an in-depth understanding of the growth mechanism. This report expands the 2D material lateral heterostructure family, which gives impetus to their applications in electronics and optoelectronics.

An improved method for controllable growth of monolayer WSe2 and its optical characterization

“…In the rapid heating method, the rapid increase in temperature suppresses the low saturated WSe2 vapor pressure produced at low temperature, so that the required high saturated WSe2 vapor pressure is transported through argon and deposited on the substrate, avoiding impurities and unstable phase sources produced during the heating process from depositing on the substrate. The stage of WSe2 source from heating up to product growth to substrate can be controlled within 10 minutes, which effectively improves the preparation efficiency of WSe2, avoids the source consumption caused by the decrease of the ratio of Se/W atoms due to long-time high temperature annealing under the traditional preparation method, and reduces the cost of WSe2 preparation [2] . The rapid heating is introduced into the furnace slide rail, and only the substrate is heated when the temperature is raised, and when the reaction temperature is reached, the evaporation source is heated rapidly and the heating time is short.…”

Lateral layered semiconductor multijunctions for novel electronic devices

“…66 A very recent work verified by Wang and co-workers demonstrated a CVD process for the fabrication of multilayer WS 2 / WSe 2 lateral heterostructures based on a similar principle of regulating the metal/chalcogen ratio in the precursors. 67 The effect of H 2 gas on the growth mode was discovered by Yoo et al…”

“…66 A very recent work verified by Wang and co-workers demonstrated a CVD process for the fabrication of multilayer WS 2 /WSe 2 lateral heterostructures based on a similar principle of regulating the metal/chalcogen ratio in the precursors. 67 The effect of H 2 gas on the growth mode was discovered by Yoo et al With the assistance of H 2 , researchers obtained monolayer MoS 2 with ultraclean surface, acting as the seed for the in-plane growth of WS 2 , finally leading to a lateral WS 2 /MoS 2 heterostructure. 68…”

Controlled Growth of Two-Dimensional Heterostructures: In-Plane Epitaxy or Vertical Stack

“…In this growth process, the structures of VHs or LHs may have the potential to form as the final products, which largely rely on the nucleation modes, i.e., top nucleation or edge nucleation. 31,32 As shown in Figure 1, top nucleation on the initial 2D layers yields VHs, while edge nucleation along the edges of firstgrown 2D layers leads to LHs. Thus, whether the heterostructures grow vertically or laterally depends on the growth kinetics, which governs the diffusion and nucleation energy.…”

“…The methods have been further applied in the growth of bilayer 2D heterostructures based on WS 2 /WSe 2 . 31 Based on the above understanding of the growth process of 2D heterostructures, it becomes a reality to design heterostructure arrays by the rational control of nucleation positions. A laser-patterning process was reported in a recent work to define defect arrays in the first grown monolayer semiconductor TMDs (s-TMDs).…”