Effects of current transportation and deep traps on leakage current and capacitance hysteresis of AlGaN/GaN HEMT

Abstract

In the temperature range of 40–320 K, we have studied the current-voltage I–V and capacitance-voltage C–V characteristics of a (Pt/Au)–Al0.2Ga0.8N/GaN/Al2O3 HEMT structure. Based on the I–V characteristics, we found that the leakage current and the three main parameter values of diodes (ideality factor n, series resistance Rs, and barrier height ΦB) were very sensitive to temperature changes. In addition, by considering the different current-transport mechanisms, the experimental data showed that the tunnelling current is the dominant element at all temperatures, which seems to be owing to a multistep tunnelling along dislocations. The C–V analysis showed an increase in the pinch-off voltage, a hysteresis phenomenon, and residual capacitance variation. This unusual behaviour, observed in the I–V and C–V characteristics, has been related to trapping and de-trapping processes of charge carriers happening in the structure. A one hole trap, with an activation energy of 0.316 eV and capture cross sections of 1.3 × 10−21 cm2, was observed in the deep-level transient spectroscopy (DLTS) spectra. DLTS measurements with different gate-voltages (Vgs) showed that this trap can be associated to an extended defect in the (Pt/Au)–Al0.2Ga0.8N/GaN/Al2O3 HEMT structure, such as threading dislocations. The relationship between the anomalies shown in the C–V-T and, I–V-T characteristics, and DLTS measurements, has been established.