Fabrication of sunlight sensitive tin oxide active layer phototransistors for photosensor applications and investigation of their electronic properties

In this thesis the effect of dielectric layer thickness on the electrical performance of SnO2 thin film transistors (TFTs) was investigated. Different thicknesses of SiO2 and HfO2 were used as dielectric layers. SnO2 used as the active layer of the transistors was deposited using the sol-gel spin coating method. Atomic force microscopy and scanning electron microscopy were used to analyze the surface morphology of the layers. The oxidation states of tin and oxygen elements forming the active layer were determined by X-ray photoelectron spectroscopy for the binding energies of Sn3d and O1s. The basic parameters of the fabricated TFTs, such as mobility, threshold voltage, and on-off current ratio, were calculated as a result of measurements in a dark environment. The thickness of the dielectric layers used played an important role in the electrical performance of the devices. Among the TFTs with SiO2 dielectric layers, the highest electrical performance was obtained in the TFT with a thickness of 150 nm with a mobility value of 7.10 cm2/Vs. In HfO2 dielectric layer TFTs, HfO2 dielectric layer TFT with 29 nm thickness showed the best electrical properties with a mobility value of 26.71 cm2/Vs. In addition to the thickness, the surface properties of the dielectric layer also played an effective role on the mobility value. The photosensitivity, photoresponse and specific detectivity values of the TFTs were calculated at different light intensities and all TFTs exhibited phototransistor behavior. The obtained results indicate that SnO2 TFT can be effectively used in photosensor applications.