A Study On Characterization Of Defects In GaN-based HEMT Devices

Due to its high mobility,high breakdown field and wide bandgap,the third generation semiconductor GaN have great application prospects in the fields of high temperature,high frequency and high power devices,military electronics and 5th generation mobile networks in the future.GaN-based high-electron-mobility transistors(HEMTs)have the advantages of GaN materials,and have high two-dimensional electron concentration and electron mobility,so that they have great competitive potential in market applications.One of the problems that restrict the further development and large-scale application of GaN based HEMT devices is the reliability of devices in various working environments.The reliability of semiconductor devices is closely related to the behavior of defects in semiconductor materials.The study of defect behavior in the process of device degradation plays an important role in exploring the mechanism of device degradation.In this paper,the degradation of enhanced p-GaN AlGaN/GaN HEMT under different electrical stresses and the behavior of traps in the degradation process are studied by using the deep level transient spectroscopy(DLTS).First of all,the deep level transient(DLTS)of the enhanced p-GaN AlGaN/GaN device are measured.Two dominant trap E₁,with activation energy of 0.57e V and apparent capture cross section of 5.4×10^-18cm^-2 and E₂,with activation energy of 0.76e V and apparent capture cross section of 1.1×10^-12cm^-2,has been observed in fresh device.It is considered that the trap E₁ is Nitrogen antisites,while the trap E₂ is Nitrogen interstitials.The experimental results show that the gate over-drive stress lead to the negative shift of the threshold voltage,the increases of concentration of trap E₂,while the trap E₁ does not change.There's also a new trap E₃ generated,with activation energy of 0.08ev,capture cross section of 1.1×10^-12cm^-2.The gate degradation could be contributed to some newly generated defects that cannot be recovered for a long time(trap E₃),Which may generated by the influence of high-energy holes.A positively charged trap is generated in the area under the gate,which is fixed on the side of the AlGaN barrier layer under the p-GaN gate,resulting in a decrease in the barrier height,also negative drift of the threshold voltage.Then,the influence of high-field stress on p-GaN AlGaN/GaN HEMTs are studied.It is found that under off-state stress,the threshold voltage of the device shows a positive shift and the drain current of the device decreases.The DLTS results shows that the concentration of trap E₁hardly changes,while of which the trap E₂increases.The activation energy deepens and capture cross section increases.It is considered that the degradation of the device may be related to the increase of trap E₂.A large number of Nitrogen interstitials(E2)are generated,forming a large amount of negative charge accumulation in the AlGaN barrier layer.It increases the the barrier height and lead to the threshold voltage positively drifted;Under the half-on stress,the concentration both of E₁and E₂ increases,which leads to the positive shift of threshold voltage and the decrease of drain current.Meantime,the activation energy of both trap E₁ and trap E₂ becomes shallower and of which the capture cross section decreases slightly.The degradation may be related to the coupling effect of trapping effect and the hot electron effect.Finally,the Silvaco TCAD was used for simulation to obtain the electric field distribution under each electrical stress condition.According to the simulation results,further research is made on the generation and changes of traps in the stress process.