Surface Modification Of PbS Quantum Dot In Photodetector Via Atomic Layer Deposition

Quantum dots（QDs）photodetectors have attracted lots of attention due to the merits of low-cost manufacturing,tunable bandgap,the compatibility with flexible substrates and multiexciton effect.Currently,the QDs photodetectors fabricated via ligand exchange approaches suffer from a large dark current,which degrades the overall performance.Atomic layer deposition（ALD）is an accurate and controllable thin film deposition technique with self-limiting surface.It can be filled with high depth-width ratio,and the deposited thin film has good uniformity and high density.At present,ALD applied in quantum dot photodetectors mainly focuses on the growth of a layer of water-oxygen barrier packaging layer to improve the stability of the device,few studies could be found on the effect of photoelectric performance of the device by ALD procedure.In this work,a precisely controlled atomic scale composite oxide infiltration method is developed to modify the QDs films via ALD.Al₂O₃ was filled in the quantum dots film by atomic layer deposition technology,the interaction between ALD precursor and PbS quantum dots surface ligand was preliminarily explored,and the influence of the filling structure parameters on the performance of the photodetector was investigated.At the same time,the filling process of Al₂O₃/ZnO composite oxides（AZO）was investigated to improve the performance of the photodetector for comparison.The main results of this thesis are as follows:1.Al₂O₃ was filled into the PbS quantum dots film by ALD,and the growth mechanism was analyzed by Fourier Transform Infrared spectroscopy（FTIR）and Quartz Crystal Microbalance（QCM）.The growth of Al₂O₃ did not destroy the long-chain ligand on the surface of the quantum dots in the micro-gap filling stage,and the carrier had a long transport distance,which made the device to exhibit a small dark current.Through X-ray photoelectron spectroscopy（XPS）,Time-Resolved Photoluminescence（TRPL）and other characterizations,it was found that Al₂O₃ filling acted as the electron acceptor for charge transfer from the quantum dots surface,and the transferred electron improved the photocurrent of the device.2.The filling process of ALD ZnO and AZO into the PbS quantum dots film was investigated by FTIR,QCM and XPS.ZnO had a high carrier mobility and improved the electron transfer efficiency in the device,which contributed to the increased photocurrent.The preparation of ZnO/PbS double-layer device was preliminarily investigated,and the spectral response range of the single-layer device was successfully broadened by UV-Vis-NIR spectra（UV-Vis-NIR）characterization.In this thesis,the study of the interaction between ALD precursors and quantum dots ligands will have certain reference significance for the application of ALD technology in quantum dots photoelectronic devices.In addition,the method of atomic-scale accurate and controllable mixed oxide filling based on ALD technology will provide a new solution for the development of nano-photoelectronic devices.