Interface engineering of multilayer cubic boron nitride terminated diamond (111): Rational regulation of Au/diamond Schottky barriers for ambipolar applications

Ultra-wide bandgap semiconductor diamond has become a new hope for developing high power devices owing to excellent properties. We have previously demonstrated that the strong Fermi pinning effect is a critical factor limiting its development. This paper proposes terminal engineering to improve the contact quality between Au and diamond by adjusting the electron affinity of the diamond (111) surface using first-principles calculations. Remarkable changes in interfacial polarity can be achieved by inserting different thicknesses of Cubic Boron Nitride (c-BN) with H/F terminals on the diamond (111) surface. The C-xBNH have the lowest negative electron affinity (-3.80 eV - -2.75 eV), whereas C-xNBF supercells have the highest positive electron affinity (4.52 eV - 8.53 eV). Positive charges accumulate at Diamond/xNB-Au and Diamond/xBNH-Au interfaces, while negative charges build up at the other interlayers. Furthermore, the tunneling probability of the Diamond/xNB-Au interfaces is close to 1, indicating an excellent transmission. The ideal p-type and n-type Schottky barrier heights can be achieved by rational design of the c-BN terminated Diamond contact with Au, and desirable ambipolar regulation can be effectively achieved (Diamond/xNB-Au (x = 2, 3) and Diamond/xNBF-Au (x = 1, 2) for n-type ohmic electrodes and Diamond/xBNF-Au (x = 2, 3) for p-type ohmic electrodes). The proposed strategy allows interface polarity optimization by modifying the surface electron affinity, which can be extended to other highperformance ambipolar diamond devices with the rational design of contact metals.