Graphene, as a two-dimensional material with high electrical conductance, has been widely investigated in contact applications. Graphene contacting with semiconductors will form a Schottky junction with non-ideal performance compared with metal contact. Graphene as an interlayer inserted between the metal contact and the semiconductor is capable of modifying the contact property by shielding the diffusion of the atoms.

Un-saturating current under reverse bias is observed in the graphene-silicon Schottky junctions. The un-saturating current becomes more pronounced with the increasing doping level of the silicon substrate. This degree of increasing reverse current is not expected in metal-semiconductor junctions and originates from the graphene contact. An improved model based on...[ Read more ]

Graphene, as a two-dimensional material with high electrical conductance, has been widely investigated in contact applications. Graphene contacting with semiconductors will form a Schottky junction with non-ideal performance compared with metal contact. Graphene as an interlayer inserted between the metal contact and the semiconductor is capable of modifying the contact property by shielding the diffusion of the atoms.

Un-saturating current under reverse bias is observed in the graphene-silicon Schottky junctions. The un-saturating current becomes more pronounced with the increasing doping level of the silicon substrate. This degree of increasing reverse current is not expected in metal-semiconductor junctions and originates from the graphene contact. An improved model based on the thermionic emission theory, which includes the additional barrier lowering effect induced by the doped graphene, is established, which predicts the enhanced un-saturating reverse current in the graphene-Si junctions.

The ideality factor extracted in the turn-on region of the graphene-silicon junctions is observed to be higher than that from the metal-contacted junctions. Through material characterization and electrical measurement, the non-ideal interface between graphene and silicon is found to be the source of the increased ideality factor. The recombination current that originated from the metal residue carried by the graphene film, plus the voltage-dividing effect across the native oxide of Si and the interface trap charges are found to be the major reason. Based on the analysis, methods to restore the ideality of the Schottky junction are also proposed.

By inserting a graphene layer between the contacting metal and the IGZO film, the Ohmic contact will be modified into a Schottky contact. With this tunneling Schottky contact, the IGZO thin film transistor is observed to have a much smaller saturation voltage in the output characteristics, which does not follow the pinch-off theory. The lower saturation voltage and higher output impedance propose to enhance the noise immunity of digital circuits constructed by this new device, allow scaling of the supply voltage and reduce the power consumption.

A primary illustration of the working mechanism has been made for the tunneling contact transistor based on the TCAD simulation results. Parameters including the work function of the contacting metal, and the thickness and doping concentration of the IGZO film have been investigated to understand their influence on the performance. The tunneling nature of the contact makes it inferior to the Ohmic contact and results in a lower current level. We propose methods to enhance the current drivability based on the working mechanism.