Origin of bound exciton emission in CVD-grown monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>MoS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Kishore K. Madapu, C. Abinash Bhuyan, Sandip Dhara
Abstract
Chemical vapor deposition (CVD) is one of the prominent techniques to realize the device-grade monolayer ${\mathrm{MoS}}_{2}$ (1L-${\mathrm{MoS}}_{2}$). Thus, it is important to understand the defects in CVD grown 1L-${\mathrm{MoS}}_{2}$ to develop the 1L-${\mathrm{MoS}}_{2}$--based optoelectronic devices. In this work, we established the origin of defect-bound exciton emission in CVD-grown 1L-${\mathrm{MoS}}_{2}$ using low-temperature photoluminescence (PL) spectroscopy. So far, the role of substrate in bound exciton emission of 1L-${\mathrm{MoS}}_{2}$ has largely been overlooked. Here, we adopted an innovative dry detachment method to delineate the effect of substrate-borne impurities on bound exciton emission. The bound exciton emission was completely absent in the detached 1L-${\mathrm{MoS}}_{2}$ flake. The role of substrate-borne impurities was established using the Raman and PL spectroscopies by qualitatively analyzing the carrier density in the film before and after detachment. Kelvin probe force microscopy was employed to gauge surface-potential change after detachment. The work function of 1L-${\mathrm{MoS}}_{2}$ was found to be increased by 90 meV after the detachment. In addition, the bound exciton emission of as-grown 1L-${\mathrm{MoS}}_{2}$ was compared for wet- and surface-energy assisted transferred 1L-${\mathrm{MoS}}_{2}$ flakes. We also found that the strength of the bound exciton emission is dependent on the heat-dissipating area of the 1L-${\mathrm{MoS}}_{2}$ flake.