| Gallium nitride(GaN)materials has many advantages such as wide band gap,high breakdown electric field,high electron mobility and high thermal conductivity,and has great application potential in the fields of radio frequency and high power.High electron mobility transistors(HEMTs)based on AlGaN/GaN heterojunction are outstanding representatives of GaN-based devices and are widely used in radar,5G communications,aviation and aerospace,etc.AlGaN/GaN HEMT devices are widely used in various scenarios of human livelihood and manufacture,but the reliability of the device still restricts its future development.And the reliability problem affected by radio frequency overdrive(RF)stress and temperature change characteristics at low temperature is worth paying attention to.This paper mainly uses electrical performance and low-frequency noise characterization methods to study the reliability of AlGaN/GaN HEMT depletion-mode devices with RF stress and low temperature characteristics.The main research work and results are as follows:The electrical characteristics and low-frequency noise characteristics of AlGaN/GaN HEMT devices before and after RF stress were studied.The experimental results show that after RF stress,the output characteristics of the device were reduced,the threshold voltage was positively drifted and the transfer characteristics were shifted to the right,and the gate-lag characteristics were degraded.In addition,through electroluminescence(EL)characterization,it is found that the channel of the device had obvious uneven luminescence after RF stress.The low frequency noise(LFN)characteristic results show that the defect state density of the device after RF stress increased by about an order of magnitude compared to before.Finally,combined with related literature,it is concluded that the device degradation mechanism is due to the highintensity electric field that induces high-energy carriers during RF stress,which leads to the increase of traps in the AlGaN barrier layer under the gate and surface layer defects near the edge of the gate.The temperature properties of AlGaN/GaN HEMT devices at low temperatures are studied.Firstly,a low-temperature experiment program under 40 K～280 K was formulated,including the construction of the test platform and the test program.Subsequently,the direct current(DC)characteristics,C-V characteristics and low-frequency noise characteristics of AlGaN/GaN HEMT devices at low temperatures were tested.The DC characteristic test found that the output characteristics of the device showed a downward trend as the temperature increased,the transfer characteristic curve shifted to the right as the temperature increased,and the gate leakage current increased slightly with the increase in temperature.In addition,it is found that the curve shifts negatively with increasing temperature from the two-dimensional electron gas(2DEG)depletion area in the capacitance-voltage(C-V)characteristic curve.The LFN experiment results show that the effective defect state density of AlGaN/GaN HEMT devices at low temperature decreases with the increase of temperature,which is mainly due to the decrease of current noise power spectrum density caused by the decrease of carrier mobility.Based on the electrical properties at low temperature and the LFN test results,it is shown that a series of changes in the electrical properties of the device at low temperatures are caused by mechanisms such as acoustic phonon scattering that lead to the decrease of electron mobility with increasing temperature. |
