| X-ray is a kind of electromagnetic wave with short wavelength and high frequency.Because of its characteristics of high energy and strong penetration,X-ray has shown important application value in industrial detection,medical diagnosis,aerospace,nuclear science and technology and other fields.With the rapid development of related fields,new requirements are put forward for the development of X-ray detectors with high sensitivity,fast response/recovery speed,low dose detection limit,high energy/spatial resolution,good stability and repeatability.In recent years,researchers have paid more and more attention to the research of new X-ray detectors and made some progress,but the performance of detectors still has a large space for improvement,and the stability of detectors also needs to be further improved.In addition,original research and independent intellectual property rights of X-ray detectors are relatively lacking in China.Compared with the indirect-conversion detector,the semiconductor X-ray direct-conversion detector has advantages of high resolution,small size,simple installation,convenient operation,etc.,and is considered as a new type of X-ray detector with great development potential.At present,the first generation of semiconductor X-ray detectors such as Si and Se on the market is relatively mature.However,due to their narrow band gap and small atomic number,their detection efficiency for high-energy rays is very low and their stability is poor.In order to further improve the performance of semiconductor X-ray detectors,it is of great significance to develop a new type of X-ray detectors with excellent performance by using semiconductor materials with low intrinsic carrier concentration and high stability.In this thesis,based on the investigation of the current research results,using ZnO and GaN as the main detecting materials and applying the theory of semiconductor device physics,a series of semiconductor X-ray detectors based on photoconductive,PN-and PIN-junction structures was developed by radio frequency magnetron sputtering technique and the sol-gel technology.Performances of X-ray detection were measured by the X-ray photoelectric remote measurement system composed of the linear accelerator,sourcemeter,Lab VIEW software platform.The impact of material properties and device structure on the sensitivity,response and recovery time,signal-to-noise ratio（SNR）and other performance were analyzed in detail.The direct-conversion X-ray detectors based on wide-bandgap ZnO and GaN semiconductors with high performance were obtained by optimizing the material and structures.The specific research contents are as follows:Firstly,ZnO thin-film and nanorod-array photoconductive X-ray detectors were prepared by sol-gel technology,magnetron sputtering technology,and hydrothermal method.The effect of preparation technology on detection performance was systematically studied.The experimental results carried out by X-ray photoelectric remote measurement system show that the photoconductive X-ray detectors based on ZnO thin films prepared by magnetron sputtering technology have a low dark current of about 10-10 A at the X-ray dose rate of 0.1 Gy/s under a bias voltage of 10 V.The sensitivity is 25.2 n C·Gy-1·cm-2 with a light and dark current ratio of 15,which is significantly higher than that of the devices based on sol-gel method.The sensitivity of the photoconductive X-ray detectors based on ZnO nanorod arrays is 783 n C·Gy-1·cm-2,but the SNR and stability are poor.Secondly,GaN/（Mg）ZnO heterojunction X-ray detectors were designed and developed using Mg doped GaN thick film（sapphire substrate）as p-type layer and（Mg）ZnO as n-type layer.The effects of absorption layer materials and impurities on the detection performance were systematically studied.The results show that when the absorption-layer sputtering duration is 120 min,the sensitivity of the junction detector is the highest,which reaches 0.24μC/Gy at a dose rate of 41.5 m Gy/s under a reverse bias voltage of 5 V.The response and recovery time are 0.45 s and 0.6 s,respectively,and the SNR is 41.7.GaN/Mg ZnO heterojunction X-ray detectors were prepared by doping ZnO with Mg to widen its bandgap and increase its resistivity.The measurement results show that the sensitivity of the detector decreased to 57.3 n C/Gy,but the SNR increased to 93.The response and recovery time were reduced to 0.4 s and 0.31 s,respectively.Finally,a PIN X-ray detector with GaN/（Mg）ZnO/（Al）ZnO structure was developed based on the optimization and improvement of PN structures above.The measurement results show that the PIN junction detector has obvious self-powered characteristics.The detectors can generate a photocurrent of about 1.1 n A at a dose rate of 41.5 m Gy/s under a reverse bias voltage of 5 V,with a sensitivity of 26.5 n C/Gy and a SNR of about 59.The response time is reduced to 100 ms.New types of X-ray direct-conversion detectors based on ZnO and GaN wide-bandgap semiconductors were successfully developed in the thesis.These studies provide practical experience and scientific reference for the development and optimization of X-ray detectors based on wide-bandgap semiconductors.The detection performance obtained in these studies have reached the level of the commercial Se X-ray detector.The self-powered characteristics of the PIN junction detectors can further expand their application scenarios,showing the good development potential. |
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