Layer and size distribution control of CVD-grown 2D MoS2 using ALD-deposited MoO3 structures as the precursor

Abstract

We study the use of atomic layer deposited MoO3 films acting as Mo precursor, in a subsequent step to grow uniform MoS2 structures with excellent layer and size control over the entire substrate by chemical vapor deposition (CVD)/sulfurization process. ALD MoO3 provides two critical advantages in CVD/sulfurization of MoS2, which are the uniform sublimation and control of the amount of the Mo precursor vapor. While uniform sublimation of the MoO3 film provides uniform Mo vapor enabling reproducible growth of MoS2 on the entire substrate, control of the amount of Mo precursor provides the size and layer tuning. This control is achieved by changing the number of cycles in the ALD process. The MoO3 films are deposited on 300 nm SiO2/Si substrates using Mo(CO)6 and remote O2 plasma at 160 °C. As-deposited ALD MoO3 films are annealed at 400 and 600 °C to demonstrate the uniform nucleation domains and sublimation taking place during CVD/sulfurization. Both as-deposited and post-annealed ALD MoO3 films are characterized using spectroscopic ellipsometry, μRaman, and FTIR-ATR and AFM. For MoS2 structures, photoluminescence measurements are additionally performed to verify mono and multi-layered formations. Sparsely dense monolayer MoS2 triangles, with an edge length of ~40 μm and a thickness of ~0.78 nm are obtained with a 150-cycle MoO3 process due to an optimal distance between the nucleation domains. Moreover, as the ALD-cycle number is increased, these nucleation domains become dense, which causes the MoS2 structures to be multi-layered. It is anticipated that our results present a new possibility of controlling the formation of 2D MoS2 structures for various optoelectronic applications.