Prominent c-axis oriented Si-doped ZnO thin film prepared at low substrate temperature in RF magnetron sputtering and its UV sensing in p-Si/n-SZO heterojunction structures

Abstract

Considering the effectiveness of silicon (Si) doping in zinc oxide (ZnO) to produce Si-doped zinc oxide (SZO) for good quality transparent and conducting oxide (TCO) films, different varieties of ZnO and SZO films have been grown by changing the substrate temperature (TS), radiofrequency (RF) power and coverage (Ψ%) on the erosion area of the ZnO target using the c-Si wafer as the source of Si dopant in RF magnetron sputtering. Prominent c-axis orientation in SZO thin films and its gradual evolution on parametric changes have been systematically studied. For undoped ZnO films grown via a gradual increase in the TS, the lattice constant (c), lattice strain and stress do not change substantially. However, the grain size significantly increases, as shown by the changes in the position and full width at half maxima (FWHM) of the X-ray diffraction (XRD) peak corresponding to the (002) plane. Increasing the RF power increases the grain size and moderately decreases the c. On the contrary, upon the introduction of Si doping and its systematic escalation at increased Ψ%, the grain size linearly decreases. Upon increasing the RF power, the grain size in the SZO network increases and the magnitude of c decreases enormously, which signify the increased substitutional incorporation of the Si dopant in its Si4+ ionized state at the Zn2+ lattice site. In the SZO samples the magnitude of c, strain and stress decrease up to a certain level and then increase at elevated substrate temperature, indicating the occurrence of increased doping via Si incorporation, in contrast, at the interstitial position in the ZnO network. The RMS roughness, average roughness and surface area increase linearly with the RF power for both ZnO and SZO films. Preliminary achievements using the SZO films toward ultraviolet (UV) sensing utilizing its p-Si/n-SZO heterojunction structures has been presented.