| dc.description.abstract | This research is aimed at metal/insulator/p-GaN gate enhancement-mode high electron mobility transistors (HEMTs) to reduce gate leakage current at high gate bias conditions. In this work, a Schottky p-GaN gate HEMT (Sample A) was fabricated as the reference. HEMTs with three different gate insulators, i.e. Al2O3 (Sample B), HfOx+Al2O3 (Sample C), and ZrO2+Al2O3 (Sample D), were investigated and compared. Possible reasons for the different characteristics between these samples were also given.
Compared with the metal/p-GaN device (Sample A), which has a threshold voltage of 0.6 V, the three metal/insulator/p-GaN devices (Sample B, C, and D) exhibit the same threshold voltage of 0.9 V. This is attributed to the additional voltage drop on the insulator layer, and a larger gate voltage is needed to turn on the channel. However, adding an insulator layer to the p-GaN layer results in the reduction of gate capacitance, and thus the saturation current at a gate voltage of 6 V. In addition, while the gate breakdown voltage of the metal/p-GaN device is 10.6 V, those of the devices with Al2O3, HfOx+Al2O3, and ZrO2+Al2O3 insulators are 14 V, 13.4 V, and 12.9 V, respectively. This shows that the insulator layer effectively reduces the tunneling of holes at the gate terminal, thereby preventing the gate terminal from collapsing. The dynamic characteristics of the devices evaluated by pulsed measurements under different bias voltages indicated that the deposition of the insulator layer causes a more significant threshold voltage shift. The bidirectional sweep and variable frequency capacitance-voltage measurements show the existence of the hysteresis effect, which are used to estimate the interface state density. The interface state density of Sample A, B, C, and D is 7.9×1011 cm-2 eV-1, 2.8×1012 cm-2 eV-1, 3.1×1012 cm-2 eV-1, and 3.2×1012 cm-2 eV-1, respectively. This work shows that adding an insulator to the p-GaN gate increases the threshold voltage and breakdown voltage at the expenses of drain current and threshold voltage shift. | en_US |