Electronic, Vibrational, Elastic, and Piezoelectric Properties of H‐, F‐Functionalized AlN Sheets

Hexagonal monolayer AlN (h‐mAlN) is an indirect wide‐gap semiconductor and is attractive for use in optoelectronic devices. Herein, first‐principles calculations are performed to study the electronic, vibrational, elastic, and piezoelectric properties of H and F‐functionalized AlN sheets. The results indicate that the H‐/F‐functionalized (FAlNH) and fully H‐functionalized (HAlNH) sheets are thermodynamically and dynamically stable. FAlNH is a direct bandgap material while HAlNH is still an indirect one. The F(H) atoms in F(H)AlNH bonded with Al act as electron acceptors whereas the H atoms bonded with N are electron donors. Some vibrational modes of these two functionalized systems differ significantly although their structures are similar. Functionalization with the H and F atoms reduces the elastic constants considerably and alters the mechanical performances of both systems. The in‐plane piezoelectric constants of the FAlNH (HAlNH) sheet increase (decrease) surprisingly to about three times (one‐third) that of h‐mAlN. However, the work functions of both systems are enhanced notably. The study provides useful information for modulating the intrinsic properties of h‐mAlN for possible applications. Studies on the H‐, F‐functionalized AlN sheets reveal that FAlNH has a direct bandgap while HAlNH has an indirect one. Some vibrational manners of these two sheets are different despite their structural similarity. Elastic constants of both systems reduce significantly. Piezoelectric constants of FAlNH increase noticeably while those of HAlNH decrease sharply although their work functions are both enhanced.