The Growth And Physical Performances Of Halide Perovskite Single Crystals For Detectors

In recent years,halide perovskites(ABX₃,A=CH₃NH₃⁺,HC（NH）₂⁺,Cs⁺,B=Pb²⁺,Sn²⁺,X=I^-,Br^-,Cl^-)attract wide attention in the field of optoelectronics due to excellent properties.The halide perovskite single crystals can be widely used in photodetectors and nuclear radiation detectors owing to extremely low trap density,long diffusion length,high carrier mobility and long lifetime.Perovskite single crystals are also used in the basic research work about defects,electrical transport,dielectric and photoelectric properties,etc.This thesis firstly studies the relationship between the solubility and the solution temperature for various halides and halide perovskites in different organic solvents,and discusses the growth mechanism of the solution method for the single crystal growth in depth.According to the related solubility curve,several perovskite single crystals have successfully been grown.The crystal quality of the perovskite single crystals was studied by high-resolution X-ray rocking curves;the optical properties of the single crystals were studied by transmittance,reflectance,and photoluminescence.Photodetectors and nuclear radiation detectors based on halide perovskite single crystals were then prepared.The light absorption and the carrier transport characteristics of the single crystals were investigated through using the current-voltage curve,time of flight analysis and admittance spectroscopy.Finally,we used energy spectrum test to study on the detection performance of these devices.The key conclusions are obtained as follows:（1）The solubility of various halides and halide perovskites.The dissolution characteristics of raw materials and products were discussed.It is worth mentioning that some halides and halide perovskites show an inverse temperature solubility behavior in specific solvents.In order to grow single crystal by solution method,the solvent with high solubility and sufficient solubility gradient with temperature should be adopted.In the supersaturated region,the spontaneous nucleation occurs,and crystal growth is unstable,while the nucleation do not happen spontaneously in the metastable zone,so the growth of single crystal with large size should be settled in the metastable region.（2）The growth and properties of CsI（Tl）single crystal.According to the solubility curve,an inverse temperature crystallization（ITC）method was used to grow halide single crystals such as CsI（Tl）single crystal.The as-grown CsI（Tl）single crystals exhibit high transparency and characteristic Tl-doped photoluminescence and X-ray excited luminescence spectra with a decay time of about 535 ns at 550 nm emission peak.The CsI（Tl）scintillator with a low Tl doping concentration of 146.7 ppm exhibits a high light yield of 119000±6000 photons/Me V,which is higher than those grown by the conventional melting method,demonstrating that the ITC method can grow high-quality single crystals,and the doping mechanism is likely unique from the traditional way.（3）The growth and properties of organo-inorganic hybrid halide perovskite single crystals.Suitable methods were chosen to grow several organic-inorganic hybrid halide perovskite single crystals according to the solubility curve,such as CH₃NH₃Pb I₃,CH₃NH₃PbBr₃,and（CH₃NH₃）₂Sn Cl₆.X-ray diffraction confirmed the acquisition of high-quality single crystals,in which CH₃NH₃Pb I₃ single crystal grows with the（200）crystal plane upside,CH₃NH₃PbBr₃ mainly grows along the（001）crystal plane,and（CH₃NH₃）₂Sn Cl₆ single crystals along the（003）and（012）crystal planes,respectively.The excellent optical properties of the perovskite single crystal were confirmed by the measurement of transmittance,reflectance and photoluminescence.（4）The growth and properties of inorganic halide perovskite CsPbBr₃ single crystal.Inorganic halide perovskite,CsPbBr₃ single crystals were grown by ITC.Comparing the full width at half-maximum（FWHM）of the characteristic peak of the high-resolution X-ray rocking curve,the FWHMs of CsPbBr₃ single crystals are around 2304±72 arcsec,while those of MAPb I₃ are only 135±9 arcsec,the MAPbBr₃ only 68±4arcsec,showing that the quality of the organic-inorganic hybrid halide perovskite single crystal grown by ITC is better than that of inorganic halide perovskite single crystal.Under the same irradiation,the photocurrent of CsPbBr₃ is about 0.212μA at 20 V bias,1.6μA for MAPbBr₃ and 9.7μA for MAPb I₃,respectively.It implies that the carrier transport of the organic-inorganic hybrid halide perovskite single crystal prepared by ITC is superior to that of inorganic halide perovskite CsPbBr₃.（5）The optimization of solution method for perovskite single crystal growth.According to the in-depth study of the growth mechanism of the solution method,a steady self-supply solution growth method based on a continuous-mass transport process（CMTP）has been designed to achieve high-quality MAPb I₃ single crystals with large size.A significantly reduced full width at half maximum of 36 arcsec of（400）plane in X-ray rocking curve,a low angular dislocation density of 6.8×10⁶ cm^-2,a low trap density of4.5×10⁹ cm^-3,a high mobility of 150.2 cm² V^-1 s^-1 and a high mobility-lifetime product of 1.6×10^-3 cm² V^-1,indicating a higher crystalline quality for the CH₃NH₃Pb I₃（MAPb I₃）single crystals grown by CMTP as compared to the conventional inverse temperature crystallized（ITC）method.The high performance of the CMTP MAPb I₃X-ray detector is comparable to that of a traditional high-quality commercial-grade Cd Zn Te device,indicating the CMTP methods being a cost-efficient strategy for high-quality electronic grade semiconductor single crystals.In this thesis,we study the relationship between solubility and temperature,and have successfully grown a variety of halide perovskite single crystals,and prepared photodetectors and nuclear radiation detectors.It is confirmed that the improved CMTP method can be used to grow high-quality halide perovskite single crystals,and is beneficial for halide perovskite single crystals becoming the mainstream material for a new generation of room temperature semiconductor nuclear radiation detectors.