Investigation of threshold voltage shift and gate leakage mechanisms in normally off AlN/Al0.05Ga0.95N HEMTs on Si substrate

Xi Liu,Weihang Zhang,Yue Hao,Liyu Fu,Jincheng Zhang,Shenglei Zhao

doi:10.1063/5.0030299

Abstract

In this study, normally off AlN/Al0.05Ga0.95N high-electron-mobility transistors (HEMTs) on a Si substrate were fabricated by adjusting the surface states of the heterostructure. The device exhibited an extremely low reverse gate leakage current of 10−7 mA/mm due to the high Schottky-barrier height for Ni/Au on AlN/Al0.05Ga0.95N. A high ION/IOFF of 108 and a low subthreshold slope of 63 mV/decade were attained for this device. Moreover, breakdown voltages of 665 V and 1000 V were reached in these devices, with a gate-to-drain distance of 26 µm, for a grounded substrate and a floating substrate, respectively. In order to evaluate the reliability of the device, bias-induced and temperature-induced threshold-voltage-instabilities were investigated. The threshold voltage of the device shifted with gate bias stress due to electrons in the channel trapped by bulk traps. Thermally activated electrons releasing from traps decreased the threshold voltage with increasing measurement temperature. This indicates that the reliability in the threshold-voltage stability for the normally off device is dominated by the deep traps in epitaxially grown AlN/Al0.05Ga0.95N. Finally, the gate leakage mechanisms in AlN/Al0.05Ga0.95N HEMTs were investigated. The reverse and forward gate leakage was dominated by Poole–Frenkel tunneling and thermionic emission, respectively.

Highlights

Off gallium nitride (GaN) power devices have attracted significant research interest in the field of power conversion systems due to their high-frequency capability and high efficiency.1,2 key advantages of normally off power devices include their fail-safe operation and simplified driving circuits
When an in situ SiN layer is grown on the AlN barrier layer, the fixed negative polarization charges at the AlN surface are neutralized by the ionized fixed positive charges (Si+) at the SiN/AlN interface
The saturated drain current is much lower than that of conventional normally off AlGaN/GaN high-electron-mobility transistors (HEMTs), which is ascribed to the high channel resistance below the gate and low sheet carrier concentration of the AlN/Al0.05Ga0.95N heterostructure

Summary

Introduction

Off gallium nitride (GaN) power devices have attracted significant research interest in the field of power conversion systems due to their high-frequency capability and high efficiency. key advantages of normally off power devices include their fail-safe operation and simplified driving circuits. Off gallium nitride (GaN) power devices have attracted significant research interest in the field of power conversion systems due to their high-frequency capability and high efficiency.. Key advantages of normally off power devices include their fail-safe operation and simplified driving circuits. In order to achieve normally off operation, a gate-recessed structure and a p-type gate are commonly used.. In a gate-recessed structure, the etching process leads to high gate leakage, which results in a weak gate voltage swing. It is possible to suppress the gate leakage current and improve the gate voltage swing by depositing a gate dielectric such as Al2O3, Hf2O3, and SiN.. The gate reliability and, in particular, threshold-voltage instability induced by interface traps, remain critical issues to be overcome in gate-recessed metal-insulator-semiconductor (MIS) GaN high-electron-mobility transistors (HEMTs). It is possible to suppress the gate leakage current and improve the gate voltage swing by depositing a gate dielectric such as Al2O3, Hf2O3, and SiN. the gate reliability and, in particular, threshold-voltage instability induced by interface traps, remain critical issues to be overcome in gate-recessed metal-insulator-semiconductor (MIS) GaN high-electron-mobility transistors (HEMTs).

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Conclusion