Piezoelectric characteristics of doped β-Ga₂O₃ monolayer: a first-principles study

Two-dimensional (2D) piezoelectric materials have been widely concerned because of their important applications in nano-piezoelectric generators. Finding two-dimensional materials with large piezoelectric effects is still a great challenge. In this work, the inversion center of the β -Ga 2 O 3 monolayer was broken by substitutional doping. Not only the in-plane piezoelectric effect but also the uncommon out-of-plane piezoelectric effect is induced in the doped β -Ga 2 O 3 monolayer. In addition, we analyzed the cause of the piezoelectric effects from their electronic properties. The values of out-of-plane (in-plane) piezoelectric coefficient for Cu-doped and Al-doped β -Ga 2 O 3 reach −4.04 (3.95) pm/V and −2.91 (0.37) pm/V, respectively. The results are comparable with those of the commonly used bulk piezoelectric materials such as α -quartz (d 11 = 2.3 pm V −1 ), AlN (d 33 = 5.1 pm V −1 ), and GaN (d 33 = 3.1 pm V −1 ), even though they are both two-dimensional structures. Our study shows a great potential application of doped β -Ga 2 O 3 monolayer in micro and nano-electromechanical devices such as smart wearables, sensors, energy converters, and micro energy collectors.