Relationship Between Kink Phenomenon and Crystal Strain in AlGaN/GaN HEMT Under High Voltage

In this study, we confirmed the dependence of voltage stress and temperature on the I–V characteristics of AlGaN/GaN high-electron mobility transistors (HEMTs) immediately after applying voltage stress. The high voltage stress and high-temperature environment intensified the kink occurrence, likely due to the expansion of the crystal strain. Results showed that, as the voltage stress increases, a crystal strain occurs in the GaN or AlGaN layer, which affects carrier transport. It has been reported that when the drain voltage is lower than 6 V, two dimensional electron gas (2DEG) is not stably formed; thus, carrier scattering occurs due to crystal distortion. Meanwhile, 2DEG stably forms above 6 V; hence, the influence of distortion is assumed to be minimal. The inflection point of the drain conductance is further calculated based on the I–V characteristics obtained from the kink phenomenon. This inflection point suggests a transition from 3D drift motion to 2DEG carrier transport. The impact of lattice scattering becomes more noticeable at drain voltages under 6 V in the I–V characteristics, where three-dimensional transport is dominant. The lattice scattering is confirmed to be relatively mitigated at drain voltages above 6 V in the I–V characteristics, where two-dimensional transport by the 2DEG is prevalent. It is reported that the lattice vibration of crystal strain due to temperature rise saturates above a certain temperature, and electron scattering also gets limited. When a certain temperature is exceeded under high electric field stress, the drain voltage, which is the inflection point, no longer changes. This is because the amount of crystal distortion due to temperature saturates and no longer affects the 2DEG.