The Study Of Optical And Electrical Properties Of ZnO And GZO Thin Films

In this dissertation,the theoretical and experimental study of optical and electrical properties of ZnO and GZO?Ga-doped ZnO?thin films have been carried out systematically.A series of new results have been obtained.Fermi-Dirac distribution for doped semiconductors and Burstein-Moss effect have been correlated to figure out the conductivity type of ZnO.Hall effect in van der Pauw configuration has been applied to reconcile our theoretical estimations which evince our assumption.Band-gap narrowing has been found in all p-type samples,whereas blue Burstein-Moss shift recorded in n-type films.AFM?Atomic Force Microscopy?analysis shows that both p-type and n-type films have almost same granular type of structure with minor change in average grain size?⁶nm to 10nm?and surface roughness rms value 3nm for thickness³15nm which points that grain size and surface roughness did not play any significant role in order to modulate the conductivity type of ZnO.XRD?X-ray Diffraction?,EDS?Energy Dispersive X-ray Spectroscopy?and XPS?X-ray Photoelectron Spectroscopy?analysis have been employed to perform the structural,chemical and elemental analysis.Hexagonal wurtzite structure has been observed in all samples.The introduction of nitrogen reduces the crystallinity of the host lattice.97%transmittance in the visible range with1.4×10^7-1cm^-11 optical conductivity have been detected.High absorption value in ultra-violet?UV?region reveals that NZO?Nitrogen-doped ZnO?thin films can be used to fabricate next-generation high-performance UV?Ultraviolet detectors?.The structural,morphological,and optical characteristics of GZO ultra-thin films were investigated using XRD,FE-SEM,in situ EDS spectroscopy,UV–VIS-IR spectroscopy and PL?Photoluminescence spectroscopy?respectively.The morphological analysis reveals the noodle,seed,and particle-like structure of GZO for GaN,sapphire and Si substrates respectively with an average grain size ranging from 5 to 20 nm.An effective mass model?EM-Model?for a particle in a cylindrical wave function of e–h pair was correlated with experimental results.The reduction in FWHM value?from 31 nm to 13 nm?of NBE?near-band-edge?emission peak and enhanced NBE intensity have been achieved with small grain size.Blueshift in the optical band gap is explained in term of grain radius by EM-model.Improved optical and structural properties were found in relation with quantum confinement effect.The current study states that grain size plays a vital role in order to tailor the optical properties of GZO thin films.Theoretically and experimentally evaluated the optoelectronic properties of GZO were correlated.Density functional theory and Hubbard U?DFT+U_d+U_p?first-principle calculations were used for the theoretical study.The pulsed laser deposition technique was used to fabricate GZO thin films on p-GaN,Al₂O₃,and p-Si substrates.XRD graphs show single crystal growth of GZO thin films with?002?preferred crystallographic orientation.The chemical composition was studied via EDS,and no other unwanted impurity-related peaks were found,which indicated the impurity-free thin film growth of GZO.FE-SEM micrographs revealed noodle,seed,and granular-like structures of GZO/GaN,GZO/Al₂O₃,and GZO/Si,respectively.Uniform growth of GZO/GaN was found due to fewer mismatches between ZnO and GaN?0.09%?.Hall Effect measurements in the Van der Pauw configuration were used to check electrical properties.The highest mobility?53 cm²/Vs?with a high carrier concentration was found with low laser shots?1800?.A 5-fold Photoluminescence enhancement in the noodle-like structure of GZO/GaN compared with GZO/Al₂O₃and GZO/Si was detected.This points toward shape-driven optical properties because the noodle-like structure is more favorable for optical enhancements in GZO thin films.Theoretical?3.539 eV?and experimental?3.54 eV?values of the band-gap were also found to be comparable.Moreover,the lowest resistivity(3.5×10^-4?.cm)with 80%transmittance is evidence that GZO is a successful alternate of ITO.We present the experimental and theoretical insights of the surface plasmon-exciton coupled photoluminescence of Ga-doped zinc oxide?GZO?,Ag@GZO and Au@GZO nanostructures.An 8-fold enhancement in the near-band-edge?NBE?photoluminescence has been recorded in the Ag@GZO architecture without insertion of a dielectric spacer.The Finite-difference time-domain?FDTD?simulation and the experimental room temperature photoluminescence consequences point that the plasmon-exciton coupling and the band gap tailoring effect contributed to the enhancement of the radiative recombination rate at the near-band-edge.The results from the current study have paved the new way towards the fabrication of low-cost,simple-architectural and high-efficient ultraviolet?UV?optical lasers and detectors.