Investigation Of High Performance CVD Diamond Radiation Detectors And Related Electronic Devices

Diamond,as an ultra-wide bandgap semiconductor material,has super radiation hardness characteristics,ultra-fast time response at picosecond level,extremely high thermal conductivity and extremely high breakdown field intensity,making it an ideal material for the next generation of strong radiation field radiation detector.With the development of synthetic diamond technology by chemical vapor deposition(CVD),CVD diamond radiation detectors(DRD)performs better than traditional silicon-based radiation detector in many applications such as high energy particle detection,high temperature environment detection by strong irradiation,pulse field detection and so on.One of the key problems in DRD research is that the performance difference is huge and the mechanism is still unclear.The proportion of high-performance DRD is very low,which is most obvious in the most critical parameter of charge collection efficiency(CCE),energy resolution,current-voltage characteristics,which seriously restricts the technical progress of DRD.In addition,with the increase in the demand for diamond irradiation imaging detection,it is urgent to develop a fully-integrated diamond pixel array radiation detector to give full play to the advantages of strong radiation hardness ability and fast response of diamond,which requires continuous research on related diamond electronic devices.At present,there is still a big gap between the performance index of DRD developed in china and the abroad research results.It is an urgent need to development in the basic research,materials,structure optimization,device process and mechanism analysis more in-depth research,fundamentally improve the domestic DRD performance obviously lag behind the international level research status.Based on the above research background,this dissertation starts from the detection principle of radiation detectors and focuses on the four working processes of DRD,namely,the energy deposition of nuclear radiation,the generation of electron hole pairs,the transport of non-equilibrium carriers and the collection of electron hole pairs.It is clear that carrier transport and collection are the key processes that restrict DRD.From diamond material characterization analysis,high quality diamond growth,new radiation detector structure,material properties and performance of relevance,using alpha particle and X-ray source to carry out the research and design the high-performance DRD,at the same time,studied the related to the pixel array corresponds to the radiation detector diamond electronics device.The specific research contents and results are as follows.1.A method of characterization and analysis of diamond materials for radiation detector application is proposed,which realizes the growth of high purity and high-quality CVD single crystal materials.According to the analysis results of material characterization and alpha particle energy spectrum of Type IIa CVD single crystal diamond samples,a material selection and testing scheme for high-performance CVD diamond radiation detector is proposed,in which PL spectrum is the most sensitive to detect the type and content of impurities.Based on the results,a high quality and high purity CVD diamond growth process was developed.The growth substrate selective selection method and surface H₂/O₂ plasma etching method are adopted to reduce the dislocation density of epitaxial CVD layer to some extent and improve the crystal quality,and the FWHM of the XRD(004)rocking curve is only 46.3 arcsec.Using 9N hydrogen growth process,slow growth method and high-pressure method to inhibit the etching of quartz window by plasma sphere,the impurity content of CVD single crystal diamond is greatly reduced.The PL spectrum results at room temperature show that the CVD single crystal diamond obtained by this growth process does not show any impurity peak,and the impurity content of the material is close to the quality of element six"electronic grade"single crystal.2.A new structure of diamond surface modulation radiation detector is proposed for the first time in the world,which realizes the first-class CCE performance in the world.we report the performance of a single crystal DRD with gold films on hydrogen-terminated diamond(H-diamond)as electrical contacts and oxygen-terminated diamond as surface isolation between electrodes.The origin-symmetric current-voltage characteristics showed excellent ohmic contact behavior.Extremely low dark current value of 7.46×10^-13 A/mm² was measured at an electric field of 1 V/?m.Thanks to the decent ohmic contact between Au and H-diamond,the CCE of electrons and holes showed a good consistency.The CCE and energy resolution of this detector were 99.01%and 0.76%for holes,and 98.6%and 1.04%for electrons under irradiation with ²⁴¹Am?-particles.A rise time of 347.4 ps of the response to a pico-second pulsed electron source was also measured.Therefore,the DRD can be used as charged particle spectrometers,and is suitable for fast timing application.3.The effects of various material properties on the CCE performance of DRD were revealed.The energy spectrum characteristics of Type IIa CVD single crystal DRD with different impurity concentration,dislocation density and thickness were studied.Combined with the results of FTIR,XRD,Raman,PL and SIMS,it was found that the main factor limiting the CCE performance of DRD was the impurity in diamond.When the concentration of nitrogen impurity increases from 5 ppb to 170 ppb,CCE decreases from 98.7%to 3.3%.As a typical lattice defect,dislocation has little effect when the dislocation density is in the order of 10⁶-10⁷ cm^-2.At the same time,in the thickness range(200?m?500?m),it is not a good method to obtain high performance DRD by simply thinning diamond crystal.Moreover,the CCE of DRD can be effectively improved by improving the CVD growth process and reducing the impurity content and dislocation density.The results show that the maximum CCE of CVD polycrystalline DRD is limited by the maximum grain size,so it cannot effectively distinguish the energy of charged particles and identify the energy spectrum of charged particles.4.High gain X-ray detection of CVD diamond was realized.Based on"electronic grade"diamond materials,the current response of hydrogen-oxygen terminated CVD single crystal DRD working in current mode to steady state x-ray dose rate of 0.108?6.157 Gy/min was studied.The results showed that the gain factor and specific sensitivity of the DRD to X-ray are increased due to the excellent ohmic contact and bulk material characteristics.At the same time,because the trap effect of the interface was suppressed,the(35)coefficient close to1 was obtained.At 200 V bias voltage(0.66 V/?m),the gain factor,signal to noise ratio(SNR),specific sensitivity and(35)coefficient of the device were 151.83,10⁴-10⁶,41.441?C/Gy·mm³ and 1.033±0.014,respectively.For the hydrogen oxygen terminated CVD polycrystalline DRD fabricated by the same process,the presence of grain boundary leads to a significant reduction of the response current.The gain factor,SNR,specific sensitivity and(35)coefficient of the detector were 3.92,2×10³-10⁵,0.9354?C/Gy·mm³ and 0.978±0.010 respectively at 300 V bias voltage(0.60 V/?m).5.An H-diamond field effect transistor with 300?-ALD-grown HfZrO_x/Al₂O₃ ferroelectric gate dielectrics was fabricated for the first time in the world.The HZrO_x/Al₂O₃/H-diamond gate-source diode exhibits a gate leakage current density smaller than 7.07×10^-5 A/cm² and a bowknot-like capacitance-voltage hysteresis in the V_GS range between 10.0 to-10.0 V.The continuous I_D-V_GS sweep of 50 cycles in the same V_GS range at V_DS=-0.1 V are in a clockwise hysteresis loop with a memory window of 7.3-9.2 V and the maximum on/off ratio of 10⁹.The minimum SS of about 58 m V/decade and the negative differential resistance(NDR)phenomenon observed in the I_D-V_DS curve at V_GS=-7.0 V was attributed to the negative capacitance characteristics brought by the HZrO_x ferroelectric gate.The V_th data for forward(-5 to-3.2 V)and reverse(2.3 to 6.0 V)sweeping transfer characteristic curves at V_DS=-0.1 V,or a?V_th as wide as memory window(MW),reflects the uniform polarization state in the whole HZrO_x dielectric.While at V_DS=-15 V,the I_D-V_GS hysteresis loop reshapes and the Vth data shift to-1.58 V and-0.02 V,and so a completely normally-off behavior appears in the saturation region.It is ascribed to that the polarization state of the HZrO_x dielectric along the channel turns to strongly nonuniform due to the large difference in V_GS and V_GD.These results indicate that HZrO_x/Al₂O₃/H-diamond metal ferroelectric insulator semiconductor field effect transistor(MFISFET)has potential prospect in diamond normally-off FETs,negative capacitance FETs and harsh environment memory applications with the advantage of high-density integration,and deserves further study.It provides a new technical scheme and lays a research foundation for the realization of diamond monolithic fully integrated pixel array detector in the future.