Gate tunneling current and quantum capacitance in metal-oxide-semiconductor devices with graphene gate electrodes

Metal-oxide-semiconductor(MOS)devices withgraphene as themetal gateelectrode,silicon dioxide with thicknesses ranging from 5 to 20  nm as the dielectric, andp-typesilicon as the semiconductor arefabricated and characterized. It is found thatFowler-Nordheim (F-N)tunneling dominates the gatetunneling current in thesedevices for oxide thicknesses of 10  nm and larger, whereas fordevices with 5  nm oxide, directtunneling starts to play a role in determining the total gate current. Furthermore, the temperature dependences of the F-Ntunneling current for the 10  nmdevices are characterized in the temperature range 77 –300 K. The F-N coefficients and the effectivetunneling barrier height are extracted as a function of temperature. It is found that the effective barrier height decreases with increasing temperature, which is in agreement with the results previously reported for conventionalMOSdevices with polysilicon ormetal gateelectrodes. In addition, high frequency capacitance-voltage measurements of theseMOSdevices are performed, which depict a localcapacitance minimum under accumulation for thin oxides. By analyzing the data using numerical calculations based on the modified density of states ofgraphene in the presence of charged impurities, it is shown that this local minimum is due to the contribution of the quantumcapacitance ofgraphene. Finally, the workfunction of thegraphene gateelectrode is extracted by determining the flat-band voltage as a function of oxide t...

Source: Applied Physics Letters - November 30, 2016 Category: Physics Authors: Yanbin An, Aniruddh Shekhawat, Ashkan Behnam, Eric Pop and Ant Ural Source Type: research