Synergistic effects of Ga doping and Mg alloying over the enhancement of the stress sensitivity of a Ga-doped MgZnO pressure sensor

Abstract

We demonstrate the synergistic effects of Ga doping and Mg alloying into ZnO on the large enhancement of the piezopotential and stress sensing performance of piezotronic pressure sensors made of Ga-doped MgZnO films. Piezopotential-induced pressure sensitivity was enhanced through the modulation of the Schottky barrier height. Doping with Ga (0.62 Å) of larger ionic radius and alloying with Mg (0.57 Å) of smaller ionic radius than Zn ions can synergistically affect the overall structural, optical and piezoelectric properties of the resulting thin films. The crystal quality of Ga-doped MgZnO films either improved (X_Ga ≦ 0.041) or deteriorated (X_Ga ≧ 0.041) depending on the Ga doping concentration. The band gap increased from 3.90 eV for pristine MgZnO to 3.93 eV at X_Ga = 0.076, and the piezoelectric coefficient (d₃₃) improved from ∼23.25 pm V⁻¹ to ∼33.17 pm V⁻¹ at an optimum Ga concentration (X_Ga = 0.027) by ∼2.65 times. The change in the Schottky barrier height ΔΦ_b increased from −4.41 meV (MgZnO) to −4.81 meV (X_Ga = 0.027) and decreased to −3.99 meV at a high Ga doping concentration (X_Ga = 0.041). The stress sensitivity (0.2 kgf) enhanced from 28.50 MPa⁻¹ for the pristine MgZnO to 31.36 MPa⁻¹ (X_Ga = 0.027) and decreased to 25.56 MPa⁻¹ at higher Ga doping concentrations, indicating the synergistic effects of Ga doping and Mg alloying over the pressure sensing performance of Ga-doped MgZnO films.