Enhanced hardness in B-doped ZnO thin films on fused quartz substrates by pulsed-laser deposition

Abstract

B-doped ZnO thin films have been fabricated on fused quartz substrates using boron–ZnO mosaic target by pulsed-laser deposition technique, and the mechanical properties have been studied by nanoindentation continuous stiffness measurement technique and transmission electron microscope (TEM). Nanoindentation measurement revealed that the hardness of B-doped ZnO films, 9.32±0.90 to 12.10±1.00GPa, is much greater than that of undoped ZnO films and very close to that of traditional semiconductor Si. The mean transmittance (%) is larger than 81% in the visible range (380–780nm) for all the films, and the Hall effect measurement showed that the carrier density is around 2×1020cm−3 and the resistivity lower than 3×10−3Ωcm. TEM characteristics show undoped thin films have more amorphous area between grains while the B-doped ZnO films have thin grain boundaries. We suggest that the grain boundaries act as the strain compensation sites and the decrease in thickness of grain boundaries enhances the hardness of the B-doped ZnO films.