In recent years, the electrical characteristics of WSe2 field effect transistors (FETs) have been widely investigated with various dielectrics. Among them, being able to perfectly tune the polarity of WSe2 is a meaningful and promising work. In this work, we systematically study the electrical properties of bilayer WSe2 FETs modulated by ferroelectric polymer poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)). Compared to traditional gate dielectric SiO2, the P(VDF-TrFE) not only can tune both electron and hole concentrations to the same high level, but also improve the hole mobility of bilayer WSe2 to 265.96 cm2V-1s-1 under SiO2 gating. Its drain current on/off ratio also has been improved to 2 × 105 for p-type and 4 × 105 for n-type driven by P(VDF-TrFE). More importantly, the ambipolar behaviors of bilayer WSe2 can be effectively achieved and maintained because of the remnant polarization field of P(VDF-TrFE). This work indicates that WSe2 FETs with P(VDF-TrFE) gating have huge potential for complementary logic transistor applications, and paves an effective way to achieve in-plane p-n junction.
Raman spectra of undoped GaAs 1−x Bi x (0<x<0.037) grown on GaAs by molecular beam epitaxy were investigated. With an increase of Bi component, we find that the longitudinal optical phonon-hole-plasmon-coupled (LOPC) mode first appears in the vicinity of the unscreened longitudinal optical (ULO) phonon frequency, and then shifts towards the transverse optical (TO) phonon frequency. A new vibrational mode (∼287 cm −1 ) between the TO and the ULO phonons was verified by use of low temperature polarized Raman measurement and the corresponding scattering intensities are found to be linearly proportional to the composition of Bi in GaAsBi. The hole concentrations determined by using the LOPC/ULO Raman intensities ratio increase from ∼6.5×10 16 to ∼2.8×10 17 cm −3 with increased Bi content and the measured results are in agreement with Hall measurements. Furthermore, the influence of excitation laser power on the estimation of the hole densities is discussed with the help of power dependent Raman spectroscopy.
In this work, we show electrical polarization of ferroelectric P (VDF-TrFE) polymer can be used to engineer the photoluminescence (PL) at bilayer WSe2. The total PL intensity substantially is suppressed under negative polarization and enhanced in positive polarization with increasing the polarization intensity of P (VDF-TrFE) polymer. And the electron transfer between conduction band energy valleys K and Λ due to built-in electric field can modify the recombination path and change the overall optical radiation efficiency, and analysis of the change is performed by the rate equation based on the charge transfer theory. The calculated intensities well reproduce the experimental results. This work may create an opportunity for hybrid integration of ferroelectric materials and 2D TMDCs as optical switch.
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