Behavior of Crystal Defects at Low Temperature in AlGaN/GaN HEMTs

In this study, the current-voltage (IV) and Radio Frequency (RF) characteristics were measured in a low-temperature environment, and the transient response waveform was analyzed by the simplified Isothermal Capacitance Transient Spectroscopy (ICTS) method. According to the measurement results of the IV characteristics, the current value decreased rapidly as the temperature decreased, and the linear region could not be confirmed. From the RF characteristics, it was confirmed that the gain varies with temperature in the high-frequency band. Furthermore, the results suggested that substantial structural changes occurred in the device under low-temperature environments. In addition, it was confirmed by simple ICTS analysis that the capture cross-section and crystal defect concentration increased with decreasing temperature. At room temperature, the thermal energy imparted to the crystal layer induces phonon scattering at crystal lattice points. This implies that the process of trapping electrons in crystal defects is suppressed. In a high-frequency region, carriers trapped in crystal defects are released and the crystal defects become conspicuous. As a result, an increase in the capacitance component of crystal defects was confirmed, and it is thought that both the capture cross-section and the crystal defect concentration increased compared to those at room temperature.