Bidirectional Threshold Voltage Shift After Positive Bias Temperature Instability of p-GaN HEMTs at Cryogenic Temperature

In this paper, the Positive Bias Temperature Instability (PBTI) in p-GaN high-electron-mobility transistors (HEMTs) at cryogenic temperatures is investigated, emphasizing the interplay between two competing mechanisms: electron trapping and hole injection. These mechanisms induce bidirectional shifts in the threshold voltage (VTH), contingent on temperature and gate voltage stress conditions. Experimental results demonstrate that at lower gate voltage, a positive VTH shift has been observed as a result of the electron trapping. Conversely, hole injection becomes the dominant mechanism as gate stress voltage increases. However, the emission of frozen electron traps reduces the net number of trapped electrons due to the trap freeze-out effect under prolonged stress, thereby enhancing the dominance of hole injection. This influences the competition between the two mechanisms at cryogenic temperatures, leading to a bidirectional VTH shift under prolonged stress. A comprehensive analysis of gate leakage current, hysteresis behavior, and extracted trap density has been conducted. Our findings provide an enhanced understanding of p-GaN HEMTs reliability for wide cryogenic applications, such as superconducting systems and space electronics.