Growth And Characterization Of Thin Film Semiconductors

Thin film metal oxide semiconductors have always been the materials of interest for various device applications due to their wide bandgap and interesting electrical properties. The role of defects in controlling these properties of the materials has also been widely known through extensive research. In order to use these materials for advanced device applications, it is necessary to characterize defects and understand their effect on the electrical properties. The main objective of this thesis is to study three different thin film metal oxide semiconductor samples of Gallium Indium Oxide named as depositions 55, 68 and 70 deposited by using the MOCVD technique. The samples were characterized to examine their electrical properties, and defects were studied to explain the origin of the electrical conductivity and resistivity shown by each of these samples. The samples were measured using Hall effect measurements for electrical characterization, and X-ray Diffraction (XRD) was used for structural characterization. Positron Annihilation Spectroscopy (PAS) technique was applied to study the vacancy type defects in these depositions. Hall effect results indicate that deposition 55 is the most conductive with high electron mobility and low value of sheet resistance, and it is found that this sample exhibits n-type conductivity. The electrical characterization data suggests that deposition 68 is the most resistive among the three depositions with high value of sheet resistance. Deposition 70 was found to exhibit n-type conductivity but showed higher value of sheet resistance as compared to deposition 55. Among the various techniques used for PAS, we applied Doppler Broadening Spectroscopy (DBS) for defects characterization of the depositions. DBS results show the presence of vacancy type defects in all of the three samples and indicate the crucial role of defects in the electrical properties exhibited by the thin films. The defects measurements were analyzed, and it is suggested that higher defect concentration are associated with higher resistivity. For deposition 68, native defects are indicated to act as deep electron traps that reduce the carrier concentration and make the sample resistive. This work has been supported by: the National Science Foundation (NSF) under grant number DMR-2005064.