On The Photoelectric Property Characterization Of Metal Oxide Semiconductor Porous Film

Metal Oxide Semiconductor (MOS), for its stability, easily synthesized and controlled aswell as its good performance, has been widely used in different areas, such as photodetector, gas sensing, solar cell, energy storage, photo catalysis and etc.. In theseapplications, the MOS has interactions not only with the induced photons, but also withthe gas molecules in the enviorment. The porous film has its advantages in the reactionwith the gas molecules because of its large specific surface area. Thus, the metal oxidesemiconductor porous film (MOSPF) has drawn great attention. In order to research therelationship of composition, structure and performance between materials and to developnovel material, the assessment of MOSPF performance under illumination is so important.Based on this point, this thesis proposed a package of solutions to evaluate thephotoelectrical performance of MOSPF, which includes the measurement platform andprocesses.The MOSPF photoelectrical performance measurement platform has been designedand set up initially. The hardware of measurement platform is consist of light sourcesmodular, environment control modular, material chip, data acquisition circuit and testchamber. And the software of the platform is coded by LabVIEW, which is the graphicalcoding language widely used in the engineering field. High throughput, test environmentcontrolling, frequency-resolved photoconductivity test and automatic testing is thehighlight of the platform. The steady-state photoconductivity test (I-V curves), thetime-resolved photoconductivity test (σ-t curves) and the frequency-resolvedphotoconductivity test (σ-λ curves) can be realized with this platform.Based on the conduction model, the current-voltage relationship of MOSPF inspecific gas circumstances under illumination has been established. The material chipwhich includes ZnO, SnO2, WO3and TiO2porous film has been synthesized and tested indark and under UV illumination with dry air and formaldehyde environment, respectively.According to the current-voltage relationship, the holes’ concentrations, the change of thedepletion layer and charge density in the depletion layer have been acquired through fitting with the help of Genetic Algorithms. It is proved that the steady-statephotoconductivity test can be used to evaluate the photocatalyic activity.The time-resovled photoconductivity curves of TiO2/SnO2MOSPF composites areacquired based on the platform. The photoconductivity amplitude and the featureparameters of the photoconductivity decay curves are extracted. In view ofphotoconductivity amplitude, the Incident Photo-to-electron Conversion Efficiency (IPCE)is proposed and used to evaluate the separation efficiency of the photon-induced electronsand holes in the composites. In the meantime, the defects’ species, density and bandstructure are extracted from the photoconductivity decay curves. These results furtherverify the conclusion of the IPCE analysis. The IPCE and photoconductivity decay curvesanalysis based on the time-resolved photoconductivity test can acquire more detailedinformation than traditional methods.The effect of doping and annealing in vacuum on the photoelectric performance ofMOSPF has been researched in the frequency-resolved photoconductivity test. The resultsshow that, the defects can be reduced by the annealing, which highlights the intrinsicphotoconductivity; while, specific defects can be introduced by the doping, which broaderthe response wavelength section. The frequency-resolved photoconductivity test is rapid,direct, accurate and in-situ when analyzing how the defect affect on photoelectricalperformance.The effects of water molecules on the MOSPF photoelectrical performance is carriedout with the help of the platform. The interaction of the water molecules and other gasmolecules (eg. volatile organic compounds) in the MOSPF photoelectrical response hasgreat influence on the time-resolved photoconductivity curves.In conclusion, the model of the MOSPF photoelectrical response is divided into twomodels: carrier concentration model and carrier mobility model. We believe that, thecarrier concentration model dominats when MOSPF’s composition or structure changes;and the carrier mobility model dominats when test environment changes.