# Self-aligned and self-limiting van der Waals epitaxy of monolayer MoS2 for scalable 2D electronics

## TL;DR

The paper introduces a new method for growing high-quality monolayer MoS2 on sapphire, using self-alignment and self-limiting growth to achieve better electronic properties.

## Contribution

A novel self-alignment and self-limiting growth mechanism for MoS2 on sapphire using MOCVD is introduced.

## Key findings

- Misoriented domains self-align and merge into a single-crystal MoS2 film during growth.
- The use of MoO2Cl2 enables self-limiting growth of MoS2.
- Achieved carrier mobilities of 66 cm²/Vs at room temperature and 749 cm²/Vs at low temperatures.

## Abstract

Unidirectional nucleation followed by seamless stitching has emerged as a promising strategy for the scalable epitaxial growth of single-crystalline monolayer transition metal dichalcogenides on sapphire substrates, which holds potential for post-silicon electronics. In contrast, here we present a different growth mechanism for single-crystalline MoS2 on c-plane sapphire via metal-organic chemical vapor deposition (MOCVD). We show that the initial nucleation generates not only 0° and antiparallel 60° domains but also low-angle twisted domains, consistent with the coincidence site lattice framework. However, these rotationally misoriented domains are observed to deterministically self-align and merge into energetically preferred 0° domain during coalescence, yielding a continuous, unidirectional single-crystal. Additionally, by employing MoO2Cl2 as a molybdenum precursor, we demonstrate that the growth of MoS2 occurs in a self-limiting manner. This epitaxial strategy is substantiated by a carrier mobility of 66 cm2/Vs at room temperature and 749 cm2/Vs at low temperatures. Our approach offers a practical and reproducible scheme for MOCVD-based van der Waals epitaxy for 2D electronics.

Previous studies have shown the importance of unidirectionally aligned domain nucleation for the growth of 2D semiconductor single crystals. Here, the authors report the observation of a self-alignment process of misoriented domains during the metal-organic chemical vapour deposition growth of 2D MoS2 on sapphire, leading to single-crystalline films with improved carrier mobility.