Study On Failure Mechanism And Reliability Of AlGaN/GaN HEMT Switch Devices With P-GaN Gate Structure

The current industrial applications driven by the development of power electronics technology,such as the energy industry and the defense industry.As typical representatives of wide bandgap semiconductor devices,AlGaN/GaN HEMT switching devices play an important role in the development of power electronics technology because of their excellent performance.Due to the unique device structure and high atomic displacement energy,AlGaN/GaN HEMT switching devices have very broad development prospects in high-frequency and high-speed applications,such as motor drive systems and space applications.However,in the actual working process,AlGaN/GaN HEMT switching devices are affected by extreme use conditions such as high frequency,high voltage,and complex irradiation environment,which cause reliability problems for the devices.Therefore,studying the performance degradation and failure mechanism of AlGaN/GaN HEMT switching devices under extreme stress and irradiation environments is of great significance for improving the application reliability of the devices.A reliability analysis method for AlGaN/GaN HEMT switching devices is proposed in this thesis which combines key electrical parameter testing and micro-area defect extraction technology.Extreme stress and irradiation environments are adopted for testing.Extreme stress contains short-circuit current（SC）,unclamped inductive switching（UIS）,and electrostatic discharge stress（ESD）.Irradiation environments contain high-energy protons,fast heavy ions,and ⁶⁰Coγ-rays.Technical studies were carried out on the reliability of devices under extreme stress and irradiation effects.The reliability and key parameter degradation characteristics of AlGaN/GaN HEMT device are discussed under the extreme stresses and radiation effect,the physical mechanisms of device performance degradation and damage are analyzed.The work and results of this thesis are as follows:1.Study on the influence of extreme stress on the reliability of AlGaN/GaN heterojunction GaN HEMT switching devices.Two typical test methods are selected to effectively evaluate the reliability of the device’s heterojunction structure.Repeated short-circuit current stress and Unclamped Inductive Switch stress tests were carried out,combined with electricity parameter testing and low-frequency noise characterization methods,the performance degradation behavior of the device is studied,and the related physical mechanism is analyzed.The performance degradation of the device after SC and UIS stresses is due to the hot electron effect produced by the high voltage and large current in the device channel during the stress test,which is trapped by the defects in the P-GaN layer and AlGaN barrier layer of the device.The trapped electrons are released during the annealing process.The captured and released process of electrons changes the carrier concentration in the device,which resulting in the change and recovery of the electrical characteristics and low-frequency noise characteristics of the device.2.Study on the influence of electrostatic discharge stress on the reliability of P-GaN gate structure GaN HEMT switching devices.A reliability analysis method reflecting the actual use environment of the device is proposed,and repeated electrostatic discharge stress tests with a negative voltage applied to the gate of the device were carried out.The related degradation mechanism of the device is analysed.After repeated transmission line pulse（TLP）stress pulses,the electrical performance of the device was severely degraded,and the internal defect density decreased by more than an order of magnitude.This is due to the injection of a large number of electrons injection from the gate of the device during the TLP stress test,which filling the defects in the P-GaN layer and AlGaN barrier layer of the device.The electrons in the two-dimensional electron gas（2DEG）of the device are depleted,which causes the degradation of the device’s performance.The electrons filled with the defects are released after the annealing,which leads to recovery of the device performance.3.Study on single-particle irradiation effects of AlGaN/GaN HEMT switching devices.The irradiation test is carried out by high-energy proton and fast heavy Bi ion with the same fluence and different energy,to simulate the actual irradiation environment of the AlGaN/GaN HEMT switch devices.A low fluence single-particle irradiation test method is proposed for AlGaN/GaN HEMT switching devices.The electrical performance degradation behavior of the device under low fluence,high energy protons,and Bi fast heavy ions is studied.The damage mechanism of the device under the single-particle irradiation effect is analyzed based on technology computer aided design（TCAD）simulation.The low fluence of protons bonding with electrons and negatively charged defect traps in the device structure,which reduces the defect trap density in the device.As a result,the device performance is improved to a certain extent.The deep-level radiation defects induced by heavy-ion radiation reduces the carrier concentration in the device structure through the carrier removal effect.At the same time,the carrier mobility is reduced by the deep-level defects after capturing electrons.Eventually,resulting in the degradation of the performance of the device.4.Study on the total dose effect of ⁶⁰Coγ-ray irradiated by AlGaN/GaN HEMT switching devices.To fully simulating various actual working conditions of the device,the ⁶⁰Coγ-ray total dose irradiation test was carried out under the three conditions:positive voltage,negative voltage,and no power applied to the device gate.The failure characteristics and damage mechanism of the device’s total dose radiation effect are studied by sensitive parameter testing technique combined with defect quantitative analysis and physical simulation.The gate voltage bias of the device has a great influence on the total dose irradiation effect.The negative surface state charge and the interface induced negative charge,which between the oxide layer and the AlGaN barrier layer,leading to the degradation of the device with a positive gate voltage underγ-ray irradiation,and the interface induced negative charge plays a major role.The performance degradation of the device with negative gate voltage underγ-ray irradiation is mainly caused by the surface state which attached by negative charge.The degradation is recovered by annealing because the surface state is unstable.There is no change in the performance of the device before and after irradiation under the condition of no power applied to the grid.This is due to the rapid recombination of electron-hole pairs generated by the irradiation.The results in this thesis can be as a reference for further improving the application reliability of AlGaN/GaN HEMT switching devices and improving the device structure and manufacturing process.