Voltage Controlled Optical Properties of Atomically Thin Semiconductors

• Joseph Fink, Chemical Engineering, University of Virginia

• Chitraleema Chakraborty, Material Science, Physics, University of Delaware

Semiconductors have emerged as an integral part of every electronic circuit. As circuitry continues to evolve, so does the need of semiconductors to be small and efficient. Transition metal dichalcogenides (TMDC) are atomically thin semiconductor materials that show promise in revolutionizing the semiconductor industry. TMDCs consist of a transition metal such as tungsten or molybdenum sandwiched between two chalcogenides typically selenium or sulfur atoms in a hexagonal pattern, angstroms in thickness. In their bulk form, TMDCs have very little electrical application as the band gap transition is indirect. As the material is exfoliated to monolayer (sometimes bilayer) coverage, the band gap switches to a direct transition, making it a viable semiconductor. As a semiconductor, TMDCs are used in field-effect transistors where a gate voltage is applied to the TMDC to control current. As a result, understanding the ability of a TMDC to be gate-tunable is highly sought after. This project focuses on integrating and automating a voltage source meter with a photoluminescence spectrometer to measure the effects of electric fields on various TMDCs. This entails understanding and configuring the measurement software, Lightfield, through python with a keithley 2400 sourcemeter to apply voltage. Necessary spectrometer and source meter functions were implemented in python including, but not limited to, setting the center wavelength, grating, and acquisition time as well as the ability to control a static or sweeping voltage between measurements. Successful integration can be shown through a photoluminescence measurement of a green LED with sweeping voltage. Photoluminescent intensity was compared to current as the applied voltage to the green LED varied verifying the control and accuracy of the measurement.