Research Of X-ray/?-ray Detection Based On Perovskites Single Crytal

Due to X-ray/?-ray of high photon energy and strong penetrability,which have been widely used in safety inspection,medical industry and industrial flaw.Among these applications,X-ray/?-ray detection is the core of modern imaging system.At present,X-ray/?-ray detection methods could be divided into two detection mechanisms.The first one is direct-detection,the detector directly converts X-ray/?-ray photons into electron-hole pairs.The other one is indirect-detection,the X-ray/?-ray is firstly converted into visible light using a scintillator,then the visible light is detected by a conventional visible CMOS or CCD device.Compared with indirect-detection,direct-detection converts X-ray/?-ray photons directly into photogenerated electron-hole pairs,in which the intermediate conversion process of visible light photons inside scintillator is avoided.As a result,direct-detection lead to a higher quantum efficiency heoretically.However,the absorber used in direct-detection requires high absorption rate,conversion rate and carrier transport to realize high performance detection.Organic-inorganic hybrid perovskite?CH₃NH₃PbX₃,X is Cl,Br or I?single crystals have the advantages of high carrier mobility,large radiation absorption coefficient,high atomic number and low-cost preparation by solution-processed method.People have already explored its application to X-ray/?-ray detection.Since the perovskite single crystal itself has a small electrical resistivity,a perovskite heterojunction containing a plurality of organic layers is usually used to reduce the dark current of the device.However,some unsolved problems happens in this organic layer heterojunction,including easy ionized under radiation with high photon energy.Consequently,additional carriers accumulated near the interfaces and lead to large dark current and unstability.Besides,the defects density of heterojunction interface is serious which limits the response speed.In order to improve these problems,here the perovskite single crystal with selenium doped to construct a built-in p-n junction is demonstrated.A CH₃NH₃PbI₃ single crystal having a built-in p-n junction structure is prepared by adjusting the concentration of selenium doping and controlling the growth temperature during the crystallization process.It replaces the perovskite single crystal detection structure with multi-layer organic layer reported in the existed literature,thereby effectively reducing the dark current of the device and accelerating the response speed of the device.The main results of this thesis are as follows:?1?To optimize the preparation process of selenium-doped CH₃NH₃PbI₃ single crystals,the CH₃NH₃PbI₃ single crystal with built-in p-n junction is prepared by precise selenium doping concentration and temperature control during the crystallization process.It is found that Se will enter into the interior of the single crystal when the crystallization temperature is higher than 110 C,forming a built-in p-n junction.The anisotropy of crystal growth occurs when the crystallization temperature exceeds 120 C.?2?The Au/Se-doped CH₃NH₃PbI₃ single crystal/Au simple structure detector is fabricated based on Se doped CH₃NH₃PbI₃ single crystal.The dark current of the device is effectively reduced by removing the organic layer in the heterojunction(when the content of Se powder in the solution was 0.4 g/L,the dark current density is about 4 nA·cm^-2 under the bias electric field of-100 V/cm),and the response speed of the device is improved?about 3us?.?3?X-ray and?-ray are separately detected by the detector prepared in this paper.The X-ray detection sensitivity of this device is as high as 21?C·Gy^-1·cm^-2;the selenium-doped CH₃NH₃PbI₃ single crystal detector is used to detect cobalt-60?-ray,the photocurrent is as high as 58 nA and the photocurrent fluctuation is less than 5 nA.