Ferroelectric Relaxor Polymer-Enhanced Two-Dimensional WSe₂ Field Effect Transistors And Tunable Multistate Rectifiers

With good air stability and high mobility,WSe2 has attracted extensive attention for p-FETs.However,the Fermi level of WSe2 is closed to the middle of the bandgap,which limits it to form low-resistance contact with metals and thus diminishes the field effect mobilities and requires high working voltage to achieve large ON/OFF ratio.Here we propose a p-doping technique on bilayer and six-layer WSe2 flakes by coating with ferroelectric relaxor polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)(P(VDF-TrFE-CFE)).Unlike other doping methods,P(VDF-TrFE-CFE)not only can modify the Fermi level of WSe2 but can also act as a gate dielectric with high dielectric constant in an FET.Dramatic enhancement of the field effect hole mobility from 27 to 170 cm2V-1S-1 on a six-layer WSe2 FET has been achieved.Moreover,an FET device based on bilayer WSe2 with P(VDF-TrFE-CFE)as the top gate dielectric is fabricated,which exhibits high p-type performance over low top gate voltage range.Furthermore,low-temperature experiments reveal the influence of the phase transition of P(VDF-TrFE-CFE)on the channel carrier density and mobility.With decrease of temperature,field effect hole mobility increases and approaches up to 900 cm 2V-1S-1 at 200 K.The combination of the p-doping and gating with P(VDF-TrFE-CFE)provides a promising solution for obtaining high-performance p-FET with 2D semiconductors.Moreover,we utilized the shifting of the Schottky barrier controlled by an electric field to achieve a muti-field tunable reversible rectifier.We designed a structure with asymmetric contact area of drain and source,and used the p-doping effect of P(VDF-TrFE-CFE)to modify the WSe2-Cr heterojunction.Thus,a rectifier with a rectification ratio over 105 and multiple symmetrical rectifying states(e.g.,full pass state,forward pass state,off state,and backward pass state)can be achieved in a single atomically thin transistor.Furthermore,we proposed light modulation to acquire more accurate rectifying states and switching characteristics with high photo-responsivity(480 AW-1)and photoresponse speed(0.41 ms).The observed features of the ambipolar n-type Schottky barrier to p-type Schottky barrier diode,which can be reversibly tuned by gate or laser,provide another possible solution for future optoelectronic-integrated chips based on atomically thin semiconducting channels.