Performance optimization of MOS-like carbon nanotube-FETs with realistic source/drain contacts based on electrostatic doping

Due to carrier band-to-band-tunneling （BTBT） through channel-source/drain contacts, conventional MOS- like Carbon Nanotube Field Effect Transistors （C-CNFETs） suffer from ambipolar conductance, which deteriorates the device performance greatly. In order to reduce such ambipolar behavior, a novel device structure based on electrostatic doping is proposed and all kinds of source/drain contacting conditions are considered in this paper. The non-equilibrium Green＇s function （NEGF） formalism based simulation results show that, with proper choice of tuning voltage, such electrostatic doping strategy can not only reduce the ambipolar conductance but also improve the sub-threshold perfor- mance, even with source/drain contacts being of Schottky type. And these are both quite desirable in circuit design to reduce the system power and improve the frequency as well. Further study reveals that the performance of the proposed design depends strongly on the choice of tuning voltage value, which should be paid much attention to obtain a proper trade-off between power and speed in application.

Edge induced band bending in van der Waals heterojunctions:A first principle study

The dangling bond free nature of two-dimensional(2D)material surface/interface makes van der Waals(vdW)heterostructure attractive for novel electronic and optoelectronic applications.But in practice,edge is unavoidable and could cause band bending at 2D material edge analog to surface/interface band bending in conventional three-dimensional(3D)materials.Here,we report a first principle simulation on edge band bending of free standing MoS2/WS2 vdW heterojunction.Due to the imbalance charges at edge,S terminated edge causes upward band bending while Mo/W terminated induces downward bending in undoped case.The edge band bending is comparable to band gap and could obviously harm electronic and optoelectronic properties.We also investigate the edge band bending of electrostatic doped heterojunction.N doping raises the edge band whereas p doping causes a decline of edge band.Heavy n doping even reverses the downward edge band bending at Mo/W terminated edge.In contrast,heavy p doping doesn’t invert the upward bending to downward.Comparing with former experiments,the expected band gap narrowing introduced by interlayer potential gradient at edge is not observed in our free-standing structures and suggests substrate’s important role in this imbalance charge induced phenomenon.

Lead halide perovskite sensitized WSe_(2) photodiodes with ultrahigh open circuit voltages

Two-dimensional semiconductors(2DSCs)have attracted considerable interests for optoelectronic devices,but are often plagued by the difficulties in tailoring the charge doping type and poor optical absorption due to their atomically thin geometry.Herein,we report a methylammonium lead iodide perovskite(CH_(3)NH_(3)PbI_(3))/2DSC heterojunction device,in which the electric-field controllable ion migration in the perovskite layer is exploited to induce reversible electron-and hole-doping effects in the underlying monolayer tungsten diselenide(WSe_(2))to form a programmable p-n photodiode.At the same time,the CH_(3)NH_(3)PbI_(3) layer functions as a highly efficient sensitization layer to greatly boost the optical absorption and external quantum efficiency(EQE)of the resulting photodiode.By asymmetrically poling the perovskite layer,gold-contacted CH_(3)NH_(3)PbI_(3)/WSe_(2) devices show a switchable open circuit voltage up to 0.78 V,along with a high EQE of 84.3%.The integration of tunable graphene-contacts further improves the photodiode performance to achieve a highest open circuit voltage of 1.08 V and a maximum EQE of 91.3%,greatly exceeding those achieved previously in 2DSC lateral diodes.Our studies establish a non-invasive approach to switch optoelectronic functions and open up a new avenue toward high-performance reconfigurable optoelectronic devices from 2DSCs.