Preparation, characterization and heterojunction applications of ZnO films doped with some rare earth elements

In this thesis, Lanthanum (La), Europium (Eu) and Erbium (Er) doped ZnO films were prepared by sol gel method using spin coating technique. The crystallinity and surface morphologies of the prepared films were examined by X-ray diffraction (XRD) pattern and field emission scanning electron microscopy (FE-SEM), respectively. The structural parameters such as crystallite size, dislocation density, lattice parameters, strain and stress were calculated from XRD patterns of the films. From the SEM images, it was observed that the film surfaces were well-coated homogeneously without cracks and pores. SEM images of the prepared films were analyzed using the ImageJ program. Surface plots were drawn and grain size, grain boundaries and surface roughness were determined. The optical properties of the films were studied using the diffuse reflectance spectra measured by UV-vis spectrophotometer. The optical band gap values were determined using differential reflectance and Kubelka-Munk theory. After the structural, morphological and optical parameters were determined, the Au/p-Si/n-ZnO/Al, Au/p-Si/n-ZnO:La/Al, Au/p-Si/n-ZnO:Eu/Al and Au/p-Si/n-ZnO:Er/Al heterojunction structures were fabricated using these films. The electrical characterization of these heterojunctions were investigated by current-voltage (I-V) measurements between -2V and +2V. From the 𝐼-𝑉 results, it was determined that these heterojunctions have rectifying properties. The ideality factor, barrier height and series resistance of the diodes were calculated by using different methods. In addition, the I-V measurements were performed at different illuminations (20-100mW/cm2) and their photodiode properties were investigated.