Interface and polarization effects induced Schottky-barrier-free contacts in two-dimensional MXene/GaN heterojunctions

Abstract

Two-dimensional (2D) atomically thin gallium nitride (GaN) nanosheets have attracted great interest in nanoelectronics and optoelectronics due to their deep-ultraviolet emission, high electron mobility, and strong excitonic effect. The realization of high-performance GaN-based devices depends on the formation of metal–semiconductor junctions (MSJs) with low-resistance Ohmic contact. On the basis of ab initio density-functional theory calculations, we show the possibility to attain Schottky-barrier-free electron (or hole) injection to 2D GaN by using MXenes (M₂XT₂, M = Hf, Nb, Zr; X = C, N; T = O, F, OH) as metal electrodes. Our results demonstrate that the electronic structures and Schottky barrier heights (SBHs) of 2D MXene/GaN heterojunctions can be tuned by the thickness and polarity of GaN sheets and surface termination of MXenes. Moreover, we reveal that the SBHs of these MSJs inherently depend on the screening effect of MXenes on the polarization of GaN and their carrier tunneling barriers are strongly related to the interfacial coupling strength. Based on the computed SBHs and tunneling probabilities, OH-terminated MXenes are identified as the most promising electrodes for the formation of low-resistance and high-speed contacts with 2D GaN.