| Nuclear radiation detection technology plays an important role in the fields of space radiation detection,nuclear medicine,nuclear physics research,military industry,and environmental protection.Compared with gas detectors and scintillator detectors in the early years,semiconductor nuclear radiation detectors are widely used due to their small size,high sensitivity,fast response and wide energy linear range.Traditional semiconductor nuclear radiation detectors are usually based on first-generation semiconductor materials,such as silicon(Si),germanium(Ge),etc.However,Si/Ge nuclear radiation detectors have problems of poor anti-radiation performance and have strict requirements on operating temperature,which will restrict their application range.As the representative of the third-generation wide band gap semiconductor material,Gallium Nitride(GaN)has the advantages of large forbidden band width,high displacement threshold energy and so on.Besides,with the development of device preparation technology,GaN shows more and more significant advantages in the field of nuclear radiation detection and has excellent application prospects in harsh environments such as high temperature and strong radiation fields.However,most of the current GaN nuclear radiation detectors applied the sandwich structure based on homogeneous epitaxial substrates.Although this type of detector has good detection performance,the high cost of GaN freestanding substrate and small substrate size will greatly limit its industrial application.Therefore,researchers have turned their attention to GaN epitaxial layer based on sapphire substrate,which is expected to greatly reduce the production and manufacturing costs and accelerate the marketization of GaN detectors.In this paper,we focus on the growth and characterization of GaN epitaxial layer on sapphire substrate,the preparation,performance test and analysis of the detector,and the main research contents are as follows:(1)The method of isoelectronic Aluminum(Al)doping is proposed to improve the crystal quality of GaN,and the high quality GaN p-i-n epitaxial layers with the total thickness of more than 14 μm(10 μm i-GaN)were grown.The epitaxial layer is characterized and analyzed by Transmission Electron Microscope(TEM),X-ray Diffraction(XRD),Photoluminescence(PL)and other test methods.The study found that the isoelectronic doped Al atoms(with the concentration of 0.214%)effectively reduce the dislocation density by blocking the generation,movement and propagation of dislocations due to the solid solution hardening effect.Due to the self-compensation effect of CGa and CN,the epitaxial layer becomes semi-insulating and the background carrier concentration can be as low as 1014 cm-3.In addition,the non-radiative recombination center in the epitaxial layer has been reduced and the surface roughness has also been improved,which provides a strong guarantee for the preparation of high-performance GaN alpha particle detectors.(2)A GaN-based alpha particle detector with isoelectronic Al doped i-layer based on sapphire substrate was prepared.The effects of different edge termination technologies on the forward and reverse characteristics of the detector were compared and studied.The study found that the combination of two-step mesa etching and Tetramethylammonium hydroxide(TMAH)solution wet etching technology can effectively suppress sidewall leakage.Through further testing and analysis of the reverse leakage,it was found that the isoelectronic Al doped GaN detector has the lower reverse leakage current and higher breakdown voltage compared with the detector based on the unintentionally doped i-GaN,and its reverse leakage mechanism are jointly determined by Variable-range Hopping Conduction(VRH)and trap-assisted Space Charge-Limited Conduction(SCLC)mechanism.(3)The energy spectrum response of the GaN-on-sapphire p-i-n alpha particle detector was measured,and the influence of doped Al on the detection performance was analyzed.On the basis of fully evaluating the current-voltage(I-V)and capacitance-voltage(C-V)characteristics of the detector,an alpha radiation source composed of 241 Am and 239Pu isotopes was used to perform radiation testing on the detector,and the back-end electronics system are combined for energy spectrum acquisition.Through the analysis of the collected energy spectrum,it was found that the energy resolution of the detector based on isoelectronic Al doped i-GaN could reach 4%at-50 V bias.This is the best energy resolution ever reported acquired by GaN alpha particle detectors on the heteroepitaxial substrates at home and abroad.In addition,the radiation damage test found that the detector still had stable electrical and detection performance when the neutron dose is 1×1013 n/cm2.The research proves that the cost-effective Al-doped thick GaN based on sapphire substrate has significant advantages and huge application potential in realizing the industrial application of GaN nuclear radiation detectors with good anti-radiation characteristics and high energy resolution. |
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