Growth-Etch Metal-Organic Chemical Vapor Deposition Approach of WS2 Atomic-Layers

TL;DR

This paper introduces a Growth-Etch MOCVD method with water vapor to produce larger, higher-quality WS2 atomic layers, overcoming previous limitations in domain size and contamination for scalable 2D semiconductor fabrication.

Contribution

The paper presents a novel GE-MOCVD technique incorporating water vapor pulses to enhance domain size and crystal quality of WS2 and WSe2 monolayers.

Findings

Significant increase in domain size compared to conventional methods.

Enhanced crystal quality demonstrated by Raman and PL spectroscopy.

Long exciton lifetimes comparable to exfoliated flakes.

Abstract

Metal organic chemical vapor deposition (MOCVD) is one of the main methodologies used for thin film fabrication in the semiconductor industry today and is considered one of the most promising routes to achieve large-scale and high-quality 2D transition metal dichalcogenides (TMDCs). However, if not taken special measures, MOCVD suffers from some serious drawbacks, such as small domain size and carbon contamination, resulting in poor optical and crystal quality, which may inhibit its implementation for the large-scale fabrication of atomic-thin semiconductors. Here we present a Growth-Etch MOCVD (GE-MOCVD) methodology, in which a small amount of water vapor is introduced during the growth, while the precursors are delivered in pulses. The evolution of the growth as a function of the amount of water vapor, the number and type of cycles and the gas composition is described. We show a significant domain size increase is achieved relative to our conventional process. The improved crystal quality of WS2 (and WSe2) domains was demonstrated by means of Raman spectroscopy, photoluminescence (PL) spectroscopy and HRTEM studies. Moreover, time-resolved PL studies show very long exciton lifetimes, comparable to those observed in mechanically exfoliated flakes. Thus, the GE-MOCVD approach presented here may facilitate their integration into a wide range of applications.