The Study On The Inorganic-Organic Photo-electronic Detector

During the postgraduate period,my work could be divided into two parts:The first part is about the sensitization mechanism of PbSe infrared photodetector when I study at CIGIT,in this work we found direct evidence to support the sensitization mechanism of lead selenide film,which will promote people to understand and applicate the theory of lead salt sensitization process;the second part is about the near-ultraviolet organic light-emitting diode based on PVK when I study in the School of Physical Science and Technology of Southwest University.In this work,we innovatively use the PVK:BCPO mixed light-emitting layer to prepare purple organic light-emitting diodes,which not only has significant device performance but also avoids the use of mercury elements that will pollute the global environment,and provides new ideas for the future use of organic materials to prepare purple light-emitting diodes.The first four chapters of this paper introduce the development history of infrared detectors,the instruments and equipment used in this experiment,the common preparation and sensitization methods and principles of lead selenide films,and also the mechanism of the current sensitization process of PbSe films,etc.,Chapter 5 introduces the development history of NUV-based organic light-emitting diodes,the specific content of this work,and the results of innovation.Chapter 1.Firstly,the introduction of this chapter summarizes the main content of the research about the sensitization mechanism of lead selenide infrared detectors.Secondly,we introduced the development history and the different types of infrared detectors.And we also introduced the materials which were chosen to be the core of infrared photodetector.Afterward,we introduced the research status of lead selenide materials and how to fabricate them in the experiment.Common preparation methods such as electrochemical deposition method with low production cost;chemical bath deposition method;molecular beam epitaxy method;and the electron beam deposition method,which way we used in this experiment due to its high-efficiency and relatively low-cost.There are also common methods to improve the performance of the thin film,such as the etching method and the thermal oxidation method?which we used in this experiment?.Finally,we introduced several theoretical explanations of the film sensitization process,such as barrier theory and the carrier separation model.In this paper,we found direct evidence to support the carrier separation model.Chapter 2,this chapter introduces some of the experimental instruments used in this experiment and the principles of these experimental instruments.For example,the electron beam evaporation instrument,which used to prepare the film;Thermogravimetric analysis is used to analyze the relationship between the quality of PbSe during the sensitization process with the sensitization temperature and time;the scanning electron microscope?SEM?used to characterize the surface morphology of the film,X-ray diffractometer?XRD?and XPS are used to analyze surface materials and valence states before and after film sensitization;there are also Hall effect measurement is used to test the electrical properties of thin films,and the Keithley4200 is used to test the periodic response of infrared detectors to the photocurrent.Chapter 3,this chapter first introduces the process and specific parameters of the film preparation in this experiment.Secondly,through thermogravimetric analysis,we could understand the relationship between the quality of lead selenide materials in sensitization with temperature and time and infer the chemical reaction process of lead selenide in it.Based on this,two groups of comparative experiments were designed?The sensitization time of the first group is the same,and the sensitization temperature is different:sensitized at 200?,250?,300?,350?,400?,500?,600?for one hour;the sensitization temperature of the second group is the same,sensitization times are different:sensitization at 200?for 1h,2h,3h,4h?,through analysis the film surface morphology and surface compound elements under different sensitization conditions,it can be concluded that temperature has a greater influence on the morphology of the film.Chapter 4,in this chapter,we first introduce the steps of the detector preparation process and specific process parameters and then use this method to make the PbSe photodetector.Then annealed it at the same conditions,which we mentioned in chapter 3.We find that in the air atmosphere the optimal sensitization conditions are annealed 1 hour at 400?.In these conditions the device-specific detection rate is 6.66×10⁸ cmHz^1/2/W,the response time is less than 1 ms,which superior to other similar devices.The most important is that we found the detector still responds to the infrared signal light at 1550 nm and 2.7 um with the zero applied bias voltage,which indicates that a built-in electric field is generated in the sensitized film.The carrier separation model proposed that the row PbSe thin film is P-type,and during the sensitization process the PbSe grains are gradually oxidized into N-type lead from outside to inside.The salt oxide forms a structure where the N-type oxide surrounds the P-type core.These PN junctions in the film cause a built-in electric field to help the photo-generated carriers to separate and transport.Therefore,this experimental phenomenon could support the carrier separation model,which can help people to understand the sensitization process of lead salt compounds better.Although the lead selenide infrared detector can work at room temperature,the dark current of the device caused by thermal noise is still large,so we use the TTPX system to test the device.We found that the dark current of the device decreased significantly at 70 K.The device-specific detection rate is the best at 150 K.The specific reasons are explained in the relevant chapters of the article.Chapter 5,In this chapter we introduced the experiments of near-UV organic light-emitting diodes based on PVK.Ultraviolet light-emitting devices are widely used in real life.But in the traditional method of preparing ultraviolet light-emitting devices,they often use the toxic heavy metal mercury element,which causes serious environmental pollution.In this experiment,the common organic polymer PVK is used as the host material to prepare the purple OLED.At the same time,to solve the problem of poor electron transmission ability of the PVK material and the position of the LUMO energy level is too high to match with other materials,we doped BCPO to make the mixed light-emitting layer.On the one hand,this design solves the environmental problems caused by mercury.On the other hand,this mixed light-emitting layer is conducive to the balance of electron and hole transport in the device,reducing the emission of the excimer complex and optimizing the device performance.We design experiments to analyze the device brightness at different doping concentrations and obtain at the optimal doping concentration the optimal device EQE is 2.6%;when the device brightness reach to 1000 cd/m²,the EQE is2.4%.We also design unipolar electronic devices to analyze why the doping concentration of BCPO is not as large as possible.This work proves that PVK-based UV organic light-emitting diodes can still have very good performance,which greatly promotes the use of ordinary organic materials instead of contaminated heavy metal mercury to prepare UV diodes.