Research On Reliability And Failure Mechanism Of Electrical Characteristics Of P-GaN Power Devices

Ga N is one of the best semiconductor materials for the most advanced power electronic technology in the future due to their advantages such as high mobility,wide band gap(3.4e V),high breakdown voltage(3.3MV / cm)and low dielectric constant(9).At the same time,the high electron mobility transistor(HEMT)made of gallium nitride can have both very low onresistance and very low leakage current.Generally,the channel of a gallium nitride device can generate two-dimensional electron gas without the gate bias.This leads to the general d-mode of gallium nitride devices.But with the demand of the power electronics industry,enhanced power devices based on p-Ga N gate structure began to be applied.In the development of pGa N gate structure devices,device reliability has become a major bottleneck restricting its further expansion of applications.This thesis mainly studies the reliability of p-Ga N gate structure HEMT devices under different stresses(electrostatic,hydrogen)based on electrical characteristics and other methods.The main research work and results include:The electrical characteristics of p-Ga N gate structure HEMT devices under ESD(ElectroStatic discharge)stress and low-frequency noise before and after stress were studied in the thesis.The experimental results show that the change in the electrical characteristics of the device is caused by the dislocation diffusion of the heterogeneous crystal lattice generated by the piezoelectric effect.The relationship between device degradation and the number of electrostatic discharges is analyzed.With the increase of the number of electrostatic discharges,the increase of the device threshold voltage and the increase of the sub-threshold slope can be observed.At the same time,the C-V characteristic of the device was tested,and the results show that after the electrostatic stress is applied,the capacitance of the depletion layer is reduced compared with that before the stress is applied,and gradually decreases with the increase of the number of stress.In addition,through the method of low-frequency noise,the defect density of the device barrier layer was extracted,and results show that the number of device defects in 700 stress cycles was doubled compared with the new device.The effects of hydrogen released by the packaging materials in a specific environment will on the reliability of the device were discussed in this work.The detailed experimental plan was made,which includes the circuit topology and specific construction of the test platform.The effects of hydrogen on the output characteristics,transfer characteristics,on-resistance and Schottky characteristics of p-Ga N structure devices were studied and analyzed.The results show that hydrogen has a certain effect on the output characteristics,transfer characteristics,on-resistance and Schottky characteristics of P-Ga N devices.In order to further study the degradation mechanism of p-Ga N HEMT devices under hydrogen effect conditions,the SCLC(Space-Charge-Limited-Conduction)model was used to fit the Schottky characteristic curve.Finally,in conjunction with relevant literature,the causes and physical mechanisms of the hydrogen effect degradation of p-Ga N devices was explored.It is found that H + generated by the ionization of hydrogen filled the defects in the device body,causing a series of electrical characteristics to change.