Effect of electrical contact on performance of WSe_(2) field effect transistors

Two-dimensional(2 D) transition metal dichalcogenides(TMDCs) such as tungsten diselenide(WSe_(2)) have spead many interesting physical properties, which may become ideal candidates to develop new generation electronic and optoelectronic devices. In order to reveal essential features of 2 D TMDCs, it is necessary to fabricate high-quality devices with reliable electrical contact. We systematically analyze the effect of graphene and metal contacts on performance of multilayered WSe_(2) field effect transistors(FETs). The temperature-dependent transport characteristics of both devices are tested.Only graphene-contacted WSe_(2) FETs are observed with the metal-insulator transition phenomenon which mainly attributes to the ultra-clean contact interface and lowered contact barrier. Further characterization on contact barrier demonstrates that graphene contact enables lower contact barrier with WSe_(2) than metal contact, since the Fermi level of graphene can be modulated by the gate bias to match the Fermi level of the channel material. We also analyze the carrier mobility of both devices under different temperatures, revealing that graphene contact can reduce the charge scattering of the device caused by ionized impurities and phonon vibrations in low and room temperature regions, respectively. This work is expected to provide reference for fabricating 2 D material devices with decent performances.

Influence of Al2O3 barrier on the interfacial electronic structure of Au/Ti/n-GaAs structures

The Au/Ti/n-GaAs structures with and without Al2O3 interfacial layer have been fabricated.The Al2O3interfacial layer has been formed on the GaAs substrate by atomic layer deposition.The effects of the interfacial layer on the current-voltage（I-V） and capacitance-voltage（C-V） characteristics of the devices have been investigated in the temperature range of 60-300 K.It has been seen that the carrier concentration from C-V characteristics for the MIS（metal/insulating layer/semiconductor） diode with Al2O3 interfacial layer has a higher value than that for the reference diode without the Al2O3 interfacial layer（MS）.Such a difference in the doping concentration has been attributed not to doping variation in the semiconductor bulk but to the presence of the Al2O3 interfacial layer because both diodes have been made on the pieces cut from the same n-type GaAs wafer.The temperaturedependent I-V characteristics of the MIS diode do not obey the thermionic emission current theory because of the presence of the Al2O3 layer.An electron tunneling factor,aδ（x）^（1/2）,value of 20.64 has been found from the I-V-T data of the MIS diode.An average value of 0.627 eV for the mean tunneling barrier height,x,presented by the Al2O3 layer has been obtained.