Reliability Research Of AlGaN/GaN HEMT Under Strong-electrical Stresses

As the third-generation semiconductor, GaN has demonstrated outstandingperformance for high-temperature, high-voltage and high-power applications for its highbreakdown voltage, thermal conductance and also saturation velocity. The typicaldevice is AlGaN/GaN HEMT and the greatest impediment today preventing the widedeployment of the devices is its limited electrical reliability. To solve the reliabilityproblems of AlGaN/GaN HEMT under electrical stresses, not only the facts （such astemperature, electrical field and magnetic field, etc） which affect the performance of thedevices should be determined, but also the degradation mechanisms under differentstress conditions need to be researched. In recent years, the reliability research ofAlGaN/GaN HEMT mainly focus on the channel degradation problems due to hotcarrier effect and the emerge of converse piezoelectric effect due to strong field. Thearticle focuses mainly on the study of device degradation mechanism caused by inversepiezoelectric effect. In order to systematically study converse piezoelectric effect,different stresses experiments are be designed.The first kind is step electrical stress experiment carried out for finding out thedegradation mechanism of AlGaN/GaN HEMT working normally. This experiment isdevided into three parts, off-state, V_ds=0state and on-state, respectively. The other kindof experiment is a constant voltage stress experiment under off-state for10000seconds.It is carried out to find the relationship among V_crit, time and voltage. Some conclusionswe got from the above experiments are followed: firstly, the lattice defects produceddue to the inverse piezoelectric effect are mainly in the area between the gate and thedrain. secondly, the degradation mechanism of AlGaN/GaN HEMT under normallywork contain both hot carrier effect and inverse piezoelectric effect. However, we findthat the leading degradation mechanism is different under different working voltages.Thirdly, critical voltage value Vcrit has relationship with stress voltage not stress time.However, stress time will influence the demage degree of the parameters andperformance of AlGaN/GaN HEMT.