Internal quantum efficiency measurements of wafer-scale CVD grown $MoS_2$ phototransistors

Here we perform photocurrent measurements on wafer-scale monolayer and few-layer CVD $MoS_2$ to demonstrate the optoelectronic capabilities of large-scale $MoS_2$ growth. The $MoS_2$ films were grown on $SiO_2$-on-silicon substrates using a Mo-precursor thermal vapor sulfurization technique and used to make back-gated field effect phototransistors. Light from a tunable supercontinuum laser was focused on the devices, while gate or source-drain voltages were varied. Photocurrent spectra of bilayer $MoS_2$ as a function of incident wavelength displays the characteristic A(673nm), B(620nm), and C(438nm) excitons commonly associated with $MoS_2$. By measuring the power of the laser at each wavelength, the external quantum efficiency (EQE) of the device is calculated. The results show a clear band edge at 690nm and corresponding in-band EQE ranging from 1-3$\%$. Internal quantum efficiency (IQE) will be found using absorption data, and optical responsivity will be calculated for different thicknesses of grown $MoS_2$. These results show progress toward $MoS_2$ photodetectors from wafer-scale 2D semiconductors and provide a path toward large area $MoS_2$ to be used as a photovoltaic material. Future experiments intend to synthesize photovoltaic architectures from these materials.