|dc.description.abstract||In this study, the device characteristics of the new GaN high electron mobility transistor (HEMT) are discussed. The research focus on: (1) Enhancement-mode (E-mode) GaN HEMT; (2) A new type of E-mode GaN HEMT with a second gate between the main gate and the drain which is connected to the source. The experimental results compare the DC characteristics of different second gate E-mode GaN HEMT structure with the single gate E-mode GaN HEMT structure. Second gate structure can suppress the saturation current (ID, sat) under on-state and high current condition and it is expected that by the design of second gate, GaN HEMT can achieve a better short-circuit capability.
The experiment includes device simulation, layout design, device processing, and DC measurement of new GaN HEMT. Device simulation use p-GaN gate HEMT to achieve E-mode operation. The second gate design of the new structure is Schottky contact and MIS contact. Through the Silvaco TCAD simulation, the characteristics show that the Schottky second gate structure reduced ID,sat to about 12% of the single gate structure, the MIS second gate reduced ID,sat to about 62% of the single gate structure, and both of them the on-resistance is increased by less than 5%.
In device processing, the Schottky second gate design is added to the E-mode p-GaN gate HEMT; the MIS second gate design is added to the Recesses-gate E-mode GaN MIS-HEMT. The measurement results show that the Schottky second gate structure is reduced to about 30% of the single gate structure, and the MIS second gate structure is reduced to 70% of the single gate structure; wherein the on-resistance is increased about 6%, and the electrical characteristics of measurement show the same trend as that simulated by Silvaco TCAD. From this electrical characteristics, it can be expected that the new structure design can improve the short circuit capability of GaN HEMT.