• Hine, Nicholas

Abstract

<jats:title>Abstract</jats:title><jats:p>Alloying enables engineering of the electronic structure of semiconductors for optoelectronic applications. Due to their similar lattice parameters, the two-dimensional semiconducting transition metal dichalcogenides of the MoWSeS group (MX<jats:sub>2</jats:sub> where M = Mo or W and X = S or Se) can be grown as high-quality materials with low defect concentrations. Here we investigate the atomic and electronic structure of Mo<jats:sub>(1−<jats:italic>x</jats:italic>)</jats:sub>W<jats:italic><jats:sub>x</jats:sub></jats:italic>S<jats:sub>2</jats:sub> alloys using a combination of high-resolution experimental techniques and simulations. Analysis of the Mo and W atomic positions in these alloys, grown by chemical vapour transport, shows that they are randomly distributed, consistent with Monte Carlo simulations that use interaction energies determined from first-principles calculations. Electronic structure parameters are directly determined from angle resolved photoemission spectroscopy measurements. These show that the spin–orbit splitting at the valence band edge increases linearly with W content from MoS<jats:sub>2</jats:sub> to WS<jats:sub>2</jats:sub>, in agreement with linear-scaling density functional theory predictions. The spin–orbit splitting at the conduction band edge is predicted to reduce to zero at intermediate compositions. Despite this, polarisation-resolved photoluminescence spectra on monolayer Mo<jats:sub>0.5</jats:sub>W<jats:sub>0.5</jats:sub>S<jats:sub>2</jats:sub> show significant circular dichroism, indicating that spin-valley locking is retained. These results demonstrate that alloying is an important tool for controlling the electronic structure of MX<jats:sub>2</jats:sub> for spintronic and valleytronic applications.</jats:p>

Topics

• density
• impedance spectroscopy
• photoluminescence
• theory
• simulation
• semiconductor
• defect
• density functional theory
• two-dimensional