Characterization of Transient Threshold Voltage Shifts in Enhancement- and Depletion-mode AlGaN/GaN Metal-Insulator-Semiconductor (MIS)-HEMTs

Both enhancement- and depletion-mode AlGaN/GaN metal-insulator-semiconductor HEMTs were fabricated with Al 2 O 3 as the gate dielectric formed by atomic layer deposition (ALD). With the common problems of threshold voltage hysteresis in AlGaN/GaN MIS-HEMTs, DC I-V and fast transient I-V as well as frequency-dependent C-V measurements were performed to characterize the threshold voltage shifts $\Delta \mathrm {V}_{\mathrm {t}\mathrm {h}}$ and hence to systematically study the underlying mechanism. The experimental results reveal that $\Delta \mathrm {V}_{\mathrm {t}\mathrm {h}}$ can be as high as 1.0 V at $\mathrm {V}_{\mathrm {G},\max }=5\mathrm {V}$ in transient I-V measurements despite the much lower values of 0.42 V in static and CV measurements. This has significant implications in using AlGaN/GaN MIS-HEMTs for high voltage switching applications. Besides, multi-frequency C-V measurements show that the primary $\Delta \mathrm {V}_{\mathrm {t}\mathrm {h}}$ is frequency independent but the second onset of voltage shifts $(\Delta \mathrm {V}_{2})$ shows obvious frequency dependence. These results imply the likely mechanism of slow (deep) Al 2 O 3 interface traps accounting for $\Delta \mathrm {V}_{1}$ hysteresis, and fast (shallow) interface traps accounting for $\Delta \mathrm {V}_{2}$.