Power Dissipation of WSe Field Effect Transistors Probed by Low-Frequency Raman Thermometry.

The ongoing shrinkage in the size of two-dimensional (2D) electronic circuitry results in high power densities during the device operation which could cause a significant temperature rise within 2D channels. One challenge in Raman thermometry of 2D materials is that the commonly used high-frequency modes do not precisely represent the temperature rise in some of 2D materials due to peak broadening and intensity weakening at elevated temperatures. In this work, we show that a low-frequency E2g2 shear mode can be used to accurately extract temperature and measure thermal boundary conductance (TBC) in back-gated tungsten diselenide (WSe2) field effect transistors (FETs), while the high-frequency peaks (E2g1 and A1g) fail to provide reliable thermal information. Our calculations indicate that the broadening of high-frequency Raman-active modes is primarily driven by anharmonic decay into pairs of longitudinal acoustic (LA) modes resulting in a weak coupling with flexural ZA branches that are responsible for the heat transfer to the substrate. We found that the TBC at the interface of WSe2 and Si/SiO2 substrate is ~16 MW/m2.K, depends on the number of WSe2 layers, and peaks for 3-4 layer stacks. Furthermore, the TBC to the substrate is highest from the layers closest to it, with each additional layer adding thermal resistance. We conclude that where heat is dissipated in a multi-layer stack is as important to device reliability as the total TBC.