Investigation Of Radiation Effects Of ?-?Semiconductor Materials And AlGaN/GaN HEMT Devices

With the development of semiconductor technology,the integration is more and more high,the size of silicon devices is approaching the physical limit.At the same time,the high integration brings new problems.The long-term reliability of micro-nano devices working in radiation environment,these problems cause the development of devices face great challenges.At present,with the rise of space industry,new semiconductor materials are widely used in satellites,space stations and other aerospace fields.High-energy heavy ions in cosmic rays can cause a single event effect on aerospace devices,as well as permanent structural damage inside the device material,which can affect the stability of the device.Therefore,it is very important to study the swift heavy ion irradiation effect on?-?semiconductor materials and devices such as InP and GaN.Irradiation experiments were performed at Heavy Ion Research Facility in Lanzhou?HIRFL?,in which the InP and GaN crystals were irradiated by Ar,Fe,Kr,Xe,Ta and Bi ions with different initial kinetic energies.The irradiation experiment was carried out under the condition of vacuum and room temperature.Aluminum foils with different thicknesses were placed in front of the samples in order to adjust the energy of SHIs,and satisfy the needs of electronic energy loss?dE/dx?_e.The transmission electron microscopy?TEM?and Raman spectroscopy were used to test the samples before and after irradiation,to systematically studied the defects as well as the morphology and size of the latent tracks.The AlGaN/GaN HEMT devices were irradiated by Xe,Ta and Bi ions under the condition of vacuum.The devices were in off-sate without bias during the irradiation process.The electrical parameters of the pristine and irradiated AlGaN/GaN HEMT devices were measured by semiconductor parameter analyzer and then a cross section TEM was used to investigate the structural damage of the devices.The cross sectional slices of the devices selected for TEM measurement were prepared by focus ion beam system?FIB?.The structure of InP crystals were damaged after irradiated with swift heavy ions.The new mode LO'was excited caused by Fe,Ar,Kr and Xe ions.According to the band structure of InP,the Raman scattering are not limited to those at the?point but extended to the whole Brillouin zone.Which indicates that defects and disorders in the crystal result in the modification of lattice vibrational modes of phonons.A peak point of the intensity ratio of LO'peak to LO peak(I_LO'/I_LO)was detected,and the corresponding fluence decreased with the increase in?dE/dx?_e.While in the case of Bi ions irradiation with a higher?dE/dx?_e,the intensity of TO mode rapid increased with the increase in ion fluences.The excitation of TO mode indicates that the crystal crystallinity changes caused by irradiation,and the results of TEM test verify this point.Therefore,the ratio of I_TO/I_LO can quantitatively describe the crystal crystallinity.Moreover,the latent tracks were observed in InP crystals and the radius of latent tracks increased with the increase in?dE/dx?_e.The fluctuation of?dE/dx?_e and Rayleigh instability lead to the formation of discontinuous tracks.The experiment results obtained by TEM and Raman directly and indirectly indicate that the structure of InP crystal were damaged.The GaN crystals were irradiated by different swift heavy ions with different energies.There was no significant change in Raman spectra of GaN crystals after irradiated by Ar,Xe,and Ta ions.While after irradiated by Fe ion,the new modes were excited in Raman spectra induced by defects state related to Ga atom and N atom.In addition,the compressive stresses increased gradually with the increase in ion fluences caused by Bi ion,which lead to the blue shift of E₂?high?mode.Raman results show that swift heavy ion irradiation will also cause the crystal structure damage in GaN material under the extreme conditions such as high?dE/dx?_e and fluences.The latent tracks were detected in GaN after irradiated by Xe,Ta and Bi ions.The radius of latent tracks increased with the increase in?dE/dx?_e.According to the experiment results reported in the literature and in this work,we conclude that the threshold of?dE/dx?_e for the track formation was about 23 keV/nm in GaN bulk material.AlGaN/GaN high electron mobility transistors?HEMTs?devices were irradiated by swift heavy ions with different fluences.From structural and electrical studies it was found that SHI irradiation leads to the significant deterioration of structural and electrical properties of the devices.After irradiation,an increase of V_th were detected in the transfer characteristic curves and a sharp decrease of I_ds were observed in output characteristic curves.The device almost failed after irradiated with Ta ions at the high fluences.Moreover,the reverse leakage current was detected in the devices irradiated by Bi ions.TCAD software were used to simulate the change of electric field distribution in the device caused by ion irradiation,it was found that the distribution of electric field restored to its initial state after 3 ns,which indicates that the degradation of electrical parameters of the devices is not related to the disturbance of electric field.In addition,the latent tracks were observed for the first time visually at the heterogeneous junction and buffer layer area in the devices after irradiation with Bi and Ta ions.The morphology and size of the latent tracks in different regions of the device were analyzed in detail.Further analyses indicate that the latent tracks induced by SHI irradiation were responsible for the degradation of the devices,which resulted in the decreased carrier mobility and sheet carrier density of 2DEG.Thus:we propose that the latent tracks play an essential role in degradation of HEMT devices.