Investigation On The Effects Of Swift Heavy Ion Irradiation In ?-Ga₂O₃ Single Crystal Material And Schottky Diodes

?-Ga₂O₃ is a new ultra-wide band gap semiconductor material with the band gap of 4.8-4.9 eV,which is much higher than that of Si(1.1 eV),Si C(3.3 eV)and GaN(3.4 eV).Moreover,the theoretical breakdown field strength is 8 MV/cm,which is almost three times that of Ga N and SiC.?-Ga₂O₃ has the advantages of high breakdown field strength,low energy loss,low cost,excellent thermal stability and chemical stability,etc.These make?-Ga₂O₃ a promising candidate material for high-frequency and high-power electronic devices.The aerospace is an important application field for power devices.The space radiation environment will cause single event effects in power devices,such as single event gate rupture and single event burnout.It can also inevitably introduce the structural damage in the devices,resulting in the performance of devices degradation or even functional failure.Therefore,it is of great significance to study the radiation damage of?-Ga₂O₃ material and device for the application of?-Ga₂O₃ in harsh radiation environments.In this thesis,different energy and fluence swift heavy ions(SHIs)were used to irradiate?-Ga₂O₃ single crystals and Schottky Diode(SBD)devices.The structure,luminescence and electrical properties of?-Ga₂O₃ samples before and after irradiation were investigated by transmission electron microscope(TEM),photoluminescence(PL),photoluminescence excitation(PLE)and semiconductor parameter analyzer,respectively.Firstly,the structure of pre-thinning?-Ga₂O₃ single crystals irradiatied with 5-13MeV/u Ta and Kr ions was investigated by TEM.The results show that:1)amorphous latent tracks were introduced in?-Ga₂O₃ single crystals after irradiation and the average diameter of latent tracks increased from 2.2 to 8.8 nm with electronic energy loss(S_e)values increasing from 18.3 to 41.5 keV/nm;2)the inelastic thermal spike model predicted that the S_e threshold of latent track formation in?-Ga₂O₃ single crystal was about 17 keV/nm for 5-13 MeV/u SHIs.The S_e threshold value seems much lower than that of other wide band semiconductors,such as Si C and Ga N.From this viewpoint,it seems that the radiation effect on?-Ga₂O₃ material by SHIs is likely to be worse than that on other wideband semiconductor materials under certain irradiation conditions.Secondly,the luminescence properties of?-Ga₂O₃ single crystals irradiated by three kinds of SHIs(Kr and Ta ions)with S_e=10.1,17.9 and 38.6 keV/nm were studied by PL and PLE spectra.The results show that:1)the?-Ga₂O₃ single crystals showed the intense luminescence at lower fluence and the collapsed luminescence with the fluence further increasing.The transition fluence of PL intensity was also related to the S_e value;2)the relative intensity of defect absorption peaks in the PLE spectra was also affected by the irradiation fluence and the S_e value.The quenching parameter Q and defects parameter D were used to quantitatively display the variation of PL and PLE spectra after irradiation.It was found that for each S_e value,the tendency of Q and D was the same with the increase of irradiation fluence.This indicates that the irradiation defects may be the main reason for the decrease of the luminescence intensity of?-Ga₂O₃ single crystal;3)according to the interaction between SHIs and target material,the luminescence model of?-Ga₂O₃ single crystal after SHIs irradiation was constructed.It is considered that there are two competing effects for SHIs irradiaiton.One is the damage effect of the latent track formation in the core region within a few nanometers along the ion trajectory.This radiation damage inhibits the luminescence of?-Ga₂O₃ single crystal.The other is the annealing effect on the grown-in defects in the outer region within a few hundred nanometers or more along the ion trajectory.This annealing effect can reduce the concentration of grow-in defects in?-Ga₂O₃ single crystal,thus promoting the luminescence.The competition between the damage effect and the annealing effect is responsible to the PL intensity variation of the irradiated?-Ga₂O₃ single crystal by SHIs with different fluence and enenrgy.Finally,semiconductor parameter analyzer and TEM were used to study the degradation and the structure damages of?-Ga₂O₃ SBD devices after 2096 MeV Ta ions irradiation.The results show that:1)the forward conduction and the reverse blocking characteristics of the irradiated?-Ga₂O₃ SBD devices degraded and the devices failed when the fluence was further increased to 5×10⁹-1×10¹⁰ ions/cm²;2)a strong carrier removal effect was observed and the carrier removal rates were 5×10⁶-1.3×10⁷ cm^-1.The amorphous latent tracks along the ions trajectories cross the whole area of drift layer,were responsible for the decrease in carrier concentration and mobility,and resulted in the deterioration of the?-Ga₂O₃ SBD devices;3)for?-Ga₂O₃devices,energetic Ta ions exhibit the highest carrier removal compared with protons and?particles.This was due to that a sinlge Ta ion can introduce the nanometer-size amorphous latent track within the depth of tens of microns,while a single proton or?particle can only introduce the atomic-size point defects;4)the carrier removal rates of?-Ga₂O₃ SBD devices are higher than that of Si C or Ga N devices(SBD and HEMTs),indicating that the worse radiation hardness of?-Ga₂O₃based device to SHIs compared with Si C and Ga N devices.This was due to the lower threshold S_evalue of latent track formation and the poor recrystallization ability for?-Ga₂O₃compared with Si C and Ga N.The damage mechanism of?-Ga₂O₃ single crystal and SBD device under SHIs irradiation were systemativally studied in this thesis.The research results may be important for?-Ga₂O₃ material to be applied in aerospace field in the future.