Two-Dimensional Transition Metal Dichalcogenides and Their Charge Carrier Mobilities in Field-Effect Transistors

Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.

Metavalent bonding impacts charge carrier transport across grain boundaries

Understanding the mechanisms underpinning the charge carrier scattering at grain boundaries is crucial to design thermoelectrics and other electronic materials.Yet,this is a very challenging task due to the complex characteristics of grain boundaries and the resulting difficulties in correlating grain boundary structures to local properties.Recent advances in characterizing charge transport across grain boundaries are reviewed,demonstrating how the microstructure,composition,chemical bonding and electrical properties of the same individual grain boundary can be correlated.A much higher potential barrier height is observed in high-angle grain boundaries.This can be ascribed to the larger number density of deep trapping states caused by the local collapse of metavalent bonding.A novel approach to study the influence of the local chemical bonding mechanism around defects on the resulting local properties is thus developed.The results provide insights into the tailoring of electronic properties of metavalently bonded compounds by engineering the characteristics of grain boundaries.

Superior multiphase interfaces in AgCuTe-based composite with significantly enhanced thermoelectric properties

It is common sense that a phase interface(or grain boundary)could be used to scatter phonons in thermoelectric(TE)materials,resulting in low thermal conductivity(k).However,a large number of impurity phases are always so harmful to the transport of carriers that poor TE performance is obtained.Here,we demonstrate that numerous superior multiphase(AgCuTe,Ag_(−2)Te,copper telluride(Cu_(2)Te and Cu_(2−x)Te),and nickel telluride(NiTe))interfaces with simultaneous strong phonon scattering and weak electron scattering could be realized in AgCuTe-based TE materials.Owing to the similar chemical bonds in these phases,the depletion region at phase interfaces,which acts as carrier scattering centers,could be ignored.Therefore,the power factor(PF)is obviously enhanced from~609 to~832μW·m^(−1)·K^(−2),and k is simultaneously decreased from~0.52 to~0.43 W·m^(−1)·K^(−1) at 636 K.Finally,a peak figure of merit(zT)of~1.23 at 636 K and an average zT(zTavg)of~1.12 in the temperature range of 523–623 K are achieved,which are one of the best values among the AgCuTe-based TE materials.This study could provide new guidance to enhance the performance by designing superior multiphase interfaces in the TE materials.

High-sensitive two-dimensional PbI_(2)photodetector with ultrashort channel

Photodetectors based on two-dimensional(2D)semiconductors have attracted many research interests owing to their excellent optoelectronic characteristics and application potential for highly integrated applications.However,the unique morphology of 2D materials also restricts the further improvement of the device performance,as the carrier transport is very susceptible to intrinsic and extrinsic environment of the materials.Here,we report the highest responsivity(172 A/W)achieved so far for a PbI_(2)-based photodetector at room temperature,which is an order of magnitude higher than previously reported.Thermal scanning probe lithography(t-SPL)was used to pattern electrodes to realize the ultrashort channel(~60 nm)in the devices.The shortening of the channel length greatly reduces the probability of the photo-generated carriers being scattered during the transport process,which increases the photocurrent density and thus the responsivity.Our work shows that the combination of emerging processing technologies and 2D materials is an effective route to shrink device size and improve device performance.