Ion-Beam-Induced Biaxial Tensile Strain Engineering in Nanoscale Zinc Oxide Films on Silicon Dioxide

Strain engineering is a powerful tool for adjusting the electrical and optical properties of materials, particularly in 2D materials on flexible polymer substrates. However, current strain-engineering techniques are primarily utilized for thin 2D materials on flexible substrates, with limited research on thicker materials on traditional substrates. In this study, the enhancement in electrical properties resulting from strain effects in 30-nm-thick ZnO films deposited on SiO₂ wafers through N₂ ion beam irradiation is proposed. The N₂ ion beam, at an optimal energy level, induces strain in the underlying SiO₂ layer, leading to a 2.5-fold increase in the saturation mobility and charge-carrier density of the overlying ZnO film. Density functional theory calculations reveal that the introduction of N₂ molecules into the SiO₂ crystal induces biaxial lattice expansion, which, in turn, strains the overlying ZnO film. These findings demonstrate the effective application of strain engineering in films of relatively large thickness, even on traditional substrates. It is anticipated that this strain engineering approach using ion-beam irradiation will significantly broaden the range of applications for strain engineering technology.