Tuning the optical band gap of monolayer WSe2 in ferroelectric field-effect transistors

Ferroelectric field-effect transistors (FeFETs) hold great promises for application in modern semiconducting industry as memory or logic devices. Intensive studies have been done on improving the performance of FeFET, which mostly rely on the electrical polarization properties of ferroelectric gate. However, the influence of the piezoelectric effect of ferroelectric gate on the semiconducting channel has not been explored to a large extent. In this work, we use gate voltage-dependent photoluminescence (PL) spectroscopy to study the piezoelectric effect of P(VDF-TrFE) gate on monolayer WSe2 channel in FeFETs. The PL peak of monolayer WSe2 undergoes a blue shift or red shift when gate voltage is applied through the ferroelectric layer, while no peak shift is observed when gate voltage is applied through the SiO2 layer. Raman spectroscopy measurements confirm the presence of in-plane strain in monolayer WSe2. Qualitative theoretical analysis and discussion suggest that the piezoelectricity of monolayer WSe2 and the P(VDF-TrFE) deformation caused by inverse piezoelectric effect are the main factors that cause strain in monolayer WSe2. These results demonstrate that the band structure of two-dimensional channel, especially monolayer two-dimensional materials, can be modulated in FeFETs, which should not be neglected under large gate voltage in FeFETs.