Engineering of Interface\nBarrier in Hybrid MXene/GaN\nHeterostructures for Schottky Diode Applications

The Fermi level position at the interface of a heterostructure\nis a critical factor for device functionality, strongly influenced\nby surface-related phenomena. In this study, contactless electroreflectance\n(CER) was utilized for the first time to investigate the built-in\nelectric field in MXene/GaN structures with the goal of understanding\nthe carrier transfer across the MXene/GaN interface. Five MXenes with\nhigh work functions were examined: Cr<sub>2</sub>C, Mo<sub>2</sub>C, V<sub>2</sub>C, V<sub>4</sub>C<sub>3</sub>, and Ti<sub>3</sub>C<sub>2</sub>. The physicochemical properties of the MXene/GaN structures\nwere analyzed by using X-ray and UV photoelectron spectroscopies.\nIt was shown that upon the coverage of the GaN surface by all investigated\nMXenes, a shift in the position of the surface Fermi level occurs,\nconsequently raising the interface barrier. Additionally, the physicochemical\nstability of MXenes on the GaN surface was studied after annealing\nthe structures at 750 °C. Our findings indicate that the annealing\nprocess increases the barrier height and the ionization energies of\nall studied structures. Furthermore, it has been shown that removing\nexcess MXene material from the surface did not significantly impact\nthe built-in electric field, emphasizing the robust physicochemical\nstability of the MXenes on the GaN surface. To validate the potential\nof engineering of MXene/GaN interface barrier, Schottky diodes with\nMXenes exhibiting the highest barrier height (Mo<sub>2</sub>C and\nV<sub>2</sub>C) were demonstrated.