Enhancing vertical piezoelectricity in Al-doped β-Ga2O3 bilayer: a first-principles study Yu-Lin Chen, Si-Lie Fu, Chun-An Wang, Jia-Yin Chen, Jing-Hua Wang, Rong-Rong Deng, Ya-Peng Xie, Xue-Lian Gao and Xian-Qiu Wu Eur. Phys. J. B, 98 5 (2025) 84 Published online: 07 May 2025 DOI: 10.1140/epjb/s10051-025-00934-1