Enhancing vertical piezoelectricity in Al-doped β-Ga2O3 bilayer: a first-principles study

With increased requirements of electronic devices for the size and the thickness of piezoelectric materials, the research of two-dimensional (2D) piezoelectric materials becomes more significant. As a fourth-generation semiconductor, β-Ga2O3 has attracted much attention owing to its superior properties. In this work, β-Ga2O3 bilayer and its doped systems were investigated through first-principles calculations. The piezoelectric effect of pristine β-Ga2O3 bilayer is induced by substitutional doping. We choose three transition metal elements (i.e., Cu, Al, and In) as dopants and find that AlIV-doped β-Ga2O3 bilayer exhibits the best stability among these studied materials. Compared with published study on β-Ga2O3 monolayer, the flexibility of bilayer structure is better than the monolayer one when doping with Al element. More importantly, the out-of-plane piezoelectric coefficient d31 of bilayer ( $$-$$ - 5.55 pm/V) is twice larger than that of monolayer ( $$-$$ - 2.55 pm/V). These values are comparable with those of conventional bulk materials, like GaN (3.1 pm/V) and α-quartz (2.3 pm/V). Our works offer a novel two-dimensional material, making doped β-Ga2O3 bilayer promising for various applications in energy collectors and piezoelectric sensors. Graphical Abstract