Exploration on electrical and optical properties of two-dimensional GaN/Al0.5Ga0.5N heterojunction under Cs, Cs/O and Cs/NF3 activation methods

In this paper, by using first principles, we conduct a detailed investigation into structural stability, charge distribution, work function and dipole moment of g-GaN (graphene-like GaN)/Al0.5Ga0.5N 2D/3D heterojunction under Cs, Cs/O and Cs/NF3 activation methods. When Cs coverage is 0.75 monolayer (ML), the band structure, density of states, absorption coefficient and reflectivity of heterojunction are also discussed. Our results indicate that adsorption energies of Cs activated heterojunctions are negative and magnify with higher Cs coverage, leading to a reduction in structural stability. Under high Cs coverage, the addition of O and NF3 enhance stability of activated heterojunctions. The interaction of Cs with heterojunction surface forms dipole 1, and the interaction with O/NF3 forms dipole 2. The influences between two dipole moments can additionally reduce surface potential barrier and work function. And the most favorable ratio of Cs to O and Cs to NF3 is 3:1. After activation, new energy levels are introduced into band structure, primarily attributed to orbital hybridization of s- and p-electron state of activator. Optical property curve show that optical performance of heterojunction can be improved by surface activation, and addition of O and NF3 will further improve optical absorption of heterojunction.