The First Principle Investigation Of Metal/Graphene/4H-SiC Contact Interface

As the third generation of semiconductor materials, SiC has been abtained wide attention in the area of high temperature, high power and high frequency electronic devices for its many excellent properties such as wide bandgap high breakdown field and high thermal conductivity. In theory, the good Ohmic contact which mainly depends on the barrier height of the metal contact on SiC is the key factor to SiC device performances. The lower the barrier is, the better it is to form good Ohmic contact. The most of ohmic contact on SiC is formed under high temperature annealing after the metal contact on SiC. In respect to the mechanisms of the formation of ohmic contact, currently a large number of studies have shown that the possible graphite intermediate layer formed maybe reduce the contact barrier height in the interface. Graphene has excellent physical properties and chemical properties such as zero bandgap and high carrier mobility which may meet the requirements of the intermediate layer. In addition, graphene has fast electron-transfer kinetics compared to the graphite. Therefore, the interface system of metal/graphene/SiC may have lower Schottky barrier and have good Ohmic characteristic, but it lacks of theoretical and experimental basis.The work tried to introduce the graphene as a transition layer into the metal/4H-SiC contact system. Based on the first principles calculation method, the reduction of schottky barrier heights (SBHs) between metal/graphene/4H-SiC interface contact systems with different graphene layers and the metal/4H-SiC contact without graphene were calculated. The interface structure, the interaction among atoms and metal induced gap states were also analysed. By optimizating the metal/graphene/4H-SiC structure, the (?)×(?)R30Si unit was found on the silicon carbide surface. This unit can simulate the interface of metal/graphene/4H-SiC reasonablly. Compared the systems without graphene, the SBH of the systems with graphene are all reduced by two kinds of calculation methods. The SBH can not be changed a lot by increasing the graphene layers for Pt, Ni and Ti systems with two to four graphene layers and Pd, Ag and Cu systems with one to four graphene layers. The SBH recuduction of the Pt, Ni and Ti systems with single-layer graphene layer is less than that with two to four graphene layers which can be due to the strong interactions between metal Pt, Ni, Ti and graphene and the different situation of metal induced gap states.The above results show that the graphene as a intermediate layer to metal/SiC contact can reduce the SBH between the contact of metal with SiC and can be beneficial to forming Ohmic contact on n-type4H-SiC.