Studying The Optoelectronic Characteristics And Charge Carrier Dynamics Based On CuInS₂ Nanocrystal Thin Film

Semiconductor nanocrystals as bridging the gap between the bulk semiconductors and molecules have attracted great attention in electronics,luminances,biological and optoelectrical fields,opening a fully new age of the development of the semiconductors.During the last decades,the semiconductor nanocrystals have succeeded in tremendous achievement at material synthesis and device fabrication,based on their unique physical and chemical characteristics.Represented by CdSe and PbS,the group II-VI and group IV-VI semiconductor nanomaterials are the most studied nanomaterials and have accessed fabulous progress,in numerous fields like lighting and energy.Furthermore,the mechanics of their growth and the physical properties have been well studied and built.Unfortunately,the existence of Cd and Pb as heave metal elements limited their further development and appliance due to their toxicity.Comparing with these nanomaterials,the group I-III-VI semiconductor nanocrystals represented by CuInS₂ and CuInSe₂ satisfying the prospect of environment-friendly green materials,thanks to their low toxicity,containing brightly potential appliance.No matter in lighting,energy or other application fields,the kinetic process of the charge carrier in the semiconductor nanocrystals domain the properties of their material and the performances of corresponding devices.However,the intrinsical physical properties of CuInS₂ related group I-III-VI nanocrystal materials need sufficient further investigation,and the charge carriers`mechanics remains partly clear.Therefore,the optoelectric properties require comprehensively characterize to lead the development of the material application.In this dissertation,the optical and electrical properties of CuInS<sub>2</sub>-based group I-III-VI semiconductor nanocrystals are studied in detail via various experimental methods.Firstly,bulk films of CuInS<sub>2</sub> semiconductor nanocrystal were prepared,and the physical properties of the I-III-VI nanocrystalline films were studied.Meanwhile,the dynamic characteristics of photo-generated carriers were investigated under various conditions.Secondly,Ag nanoparticles inserted CuInS<sub>2</sub> mixing nanocrystal thin films were fabricated to study the effect of Ag nanoparticles on the optoelectrical properties and carrier dynamics of group I-III-VI nanocrystal semiconductors.Finally,the Mn-doped CuIn<sub>2</sub>S<sub>4</sub> nanocrystal thin film optocal-switch device with brief structure was prepared,so as to analyze the optoelectrical properties and the photo-generated charge carriers`relaxation process.The kinetics of the non-equilibrium state charge carriers were also characterized under various conditions.The research results are as follows:1.Carrier behavior in CuInS₂ thin films on femtosecond and microsecond time scales is discussed in detail.The transient absorption data shows that the photo-generated carriers relax rapidly accompanied by energy change.The photo-generated charge carriers are extracted by a bias electric field?E?in the nanosecond transient photocurrent system;moreover,E would improve the efficiency of photon conversion to charge carriers and enhance the velocity of extracted charge carriers.In addition,there is a threshold of illumination intensity in the extraction process of charge carriers in the CuInS₂ thin film.Carrier recombination occurs when the illumination is higher than the threshold.The corresponding loss further increases with illumination intensity and the recombination percentage is almost independent of E.The results are useful to further understand the characteristics of carriers in the CuInS₂ thin film and are important for the operation of the corresponding optoelectronic devices.2.Opto-electronic characteristics of CuInS₂ thin film composed of Ag nanoparticles?NPs?is scanned by multi-optoelectronic test techniques.The electrochemical impedance spectroscopy shows that Ag NPs would decrease the effective resistance in CuInS₂ film.The number of photo-generated carriers has obviously increased based on the data of nanosecond transient photocurrent.The transient absorption data points out that Ag NPs increase the exciton energy in the CuInS₂ film.That facilitates the dissociation of exciton and improves the yield of photo-generated carriers,which increases the number of photo-generated carriers.The results are useful to further understand the characteristics of carriers in the CuInS₂ thin film and are important for the operation of the corresponding optoelectronic devices.3.Low-toxicity zinc blende Mn-CuIn₂S₄ thin films and a corresponding optical switch were fabricated and examined using multiple measurements.Transient absorption spectroscopy indicated that multiple carrier processes occurred during carrier relaxation.The optical switch devices showed good responsivity and stability.The kinetics of the photo-generated charge carriers were affected by carrier concentration and showed no electric-field dependence.These prepared devices showed potential for rapid photodetection applications.