MXenes-Based Electrode Selection Strategy for 2D GaN Optoelectronic Devices

Metal–semiconductor contact behavior is one of the key scientific issues in the selection of electrode materials for optoelectronic devices. In this work, on the basis of detailed first-principles calculations, we have explored the possibility of MXene phases as electrode materials for two-dimensional (2D) GaN. The calculated results reveal that high-quality n-type Ohmic contact with superior (100%) tunneling probability (TB) could be realized in the GaN monolayer (ML) by coupling bare and OH-functionalized M3N2 (M = Hf, Nb, and Zr) under the b-1(b-2) and OH-3 configurations, respectively. n- or p-type Schottky contact with a low TB is exhibited by coupling F- and O-functionalized MXenes. All these results stem from the fact that interactions at the interfaces of MXene-GaN vertical heterostructures (VHSs) are highly MXene- and configuration-dependent. The covalent and van der Waals type characterized interactions in VHSs contacting bare (b-1 and b-2) and group-functionalized MXenes indicate the strong and weak Fermi level pinning effects, respectively. As a result, irrespective of M specials, by carefully controlling the stacking pattern, bare MXenes could be used as high-quality n-type Ohmic electrode materials for GaN ML. Meanwhile, tunable Schottky barrier heights are expected to be achieved either by changing the functional group (–F, –O, or –OH) of MXenes or by selecting F-(O-) functionalized MXenes characterized by different M-specials. Our work has clarified the metal–semiconductor contact behavior in MXene-GaN VHSs and provided a selection strategy for MXenes-based electrodes suitable for GaN ML, which helps give theoretical guidance for future experiments on 2D GaN-based optoelectronic devices.