Changes in the electrical properties and the trap characteristics of AlGaN/GaN high electron mobility transistors under the application of reverse bias stress at both room temperature and low temperature were investigated. When the critical stress voltage was reached, the gate current, which complied with the Poole-Frenkel conduction conditions, showed an abrupt increase. Furthermore, the magnitude of the critical stress voltage for occurrence of the inverse piezoelectric effect can be increased at 83 K. The transient current method was used to establish that the detrapping peak amplitudes of the traps increased, but the trap activation energy remained unchanged. The changes observed in both the time constant spectra and the pulsed current-voltage curves confirmed that the trap densities in the AlGaN barrier layer increased as a result of the inverse piezoelectric effect. However, the different degrees to which the numbers of traps increased at room temperature and at 83 K contributed to the occurrence of different degradations in the device.

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The trap characteristics and polarization effect on the trapping behavior in Hf0.5Zr0.5O2 ferroelectric field-effect transistors were analyzed. The current transient that corresponds to the trapping/detrapping of charge carriers was measured and the exact time constant spectra were extracted. In accordance with the different time constants and activation energies as well as the dependence of the trapping behavior on the filling conditions, traps that originated from the oxygen vacancies in the Hf0.5Zr0.5O2 layer and from the Si/SiO2 interface trap states were identified. The detrapping peaks in time constant spectra showed a consistent changing trend with the variation of remanent polarization, confirming that the positive polarization enhanced the trapping of charge carriers injected from channel side to the ferroelectric layer.