Control of Ni/β-Ga₂O₃ Vertical Schottky Diode Output Parameters at Forward Bias by Insertion of a Graphene Layer

Controlling the Schottky barrier height (φ_B) and other parameters of Schottky barrier diodes (SBD) is critical for many applications. In this work, the effect of inserting a graphene interfacial monolayer between a Ni Schottky metal and a β-Ga₂O₃ semiconductor was investigated using numerical simulation. We confirmed that the simulation-based on Ni workfunction, interfacial trap concentration, and surface electron affinity was well-matched with the actual device characterization. Insertion of the graphene layer achieved a remarkable decrease in the barrier height (φ_B), from 1.32 to 0.43 eV, and in the series resistance (R_s), from 60.3 to 2.90 mΩ.cm². However, the saturation current (J_s) increased from 1.26×10^-11 to 8.3×10^-7(A/cm²). The effects of a graphene bandgap and workfunction were studied. With an increase in the graphene workfunction and bandgap, the Schottky barrier height and series resistance increased and the saturation current decreased. This behavior was related to the tunneling rate variations in the graphene layer. Therefore, control of Schottky barrier diode output parameters was achieved by monitoring the tunneling rate in the graphene layer (through the control of the bandgap) and by controlling the Schottky barrier height according to the Schottky-Mott role (through the control of the workfunction). Furthermore, a zero-bandgap and low-workfunction graphene layer behaves as an ohmic contact, which is in agreement with published results.