Preparation of n-type and p-type ZnO thin films and investigation of their structural, optical, and electrical properties

In this thesis, cobalt doped and undoped ZnO thin films were prepared by sol-gel chemical method. The structural, morphological, optical and electrical properties of the prepared films were investigated. According to XRD results, peak intensities increase in cobalt doped films. Measurements performed with UV-Vis spectrometer show that the band gaps of the samples vary between 3.27 eV and 3.31 eV. According to electrical measurements, undoped ZnO films show n-type properties and cobalt doped samples have p-type properties. pn junction structures were successfully formed with the prepared films. Measurements performed under UV light confirm that pn junction structures exhibit photodetector properties without applying any external voltage. The prepared pn junction photodetectors were subjected to heat treatment in two different environments, air and vacuum. The photosensitivity of 1%, 3% and 5% cobalt doped samples annealed in air were 306%, 451% and 271%, respectively, while these values were 2226%, 10301% and 34053% in samples annealed in vacuum. The photoresponse values of 1%, 3% and 5% cobalt doped samples annealed in air were 99 µA/W, 47 µA/W and 95 µA/W, respectively, while these values were 120 µA/W, 273 µA/W and 255 µA/W in samples annealed in vacuum. The results obtained in this study show that cobalt doped ZnO films exhibit p-type electrical properties and that pn junction structures can be formed with undoped ZnO films. It is also concluded that the annealing environment significantly affects the performance of the devices.