Fabrication And Characterization Of Recessed-gate MOS-HEMTs

Gallium nitride-based high-electron-mobility transistors (HEMT) are extremely promising for microwave and mm-wave power electronics applications because of their high breakdown field and high saturation velocity. However, there still remained a large gate leakage and current collapse. AlGaN/GaN MOS-HEMT with a thin high-k dielectric film is the effective solution to reduce the high gate leakage current. But the interface-trap issue and the reduction of transconductance were induced by high-k dielectric in MOS-HEMT. In this paper, we demonstrated the performance of GaN-based recessed-gate Al2O3 MOS-HEMT. On this basis, recessed-gate MOS-HEMT is optimized to achieve the desired results in the gate leakage, interface properties and the current collapse characteristics.First, the device characteristics of GaN HEMT and GaN MOS-HEMT with recessed-gate structure were analyzed by using Silvaco. With increasing recessed-gate depth, the electric field at the drain side of the gate edge increases, and the threshold shifts to positive.We demonstrated the fabrication and characterization of GaN recessed-gate MOS-HEMT. The recessed-gate structure can effectively reduce an effect on negative drift of threshold voltage. The interface-trap density has reduced obviously without any new type of trap generation. So the gate leakage current of MOS-HEMT is about three orders of magnitude lower than of AlGaN/GaN HEMT, and the current collapse can be controlled effectually. The power characteristic measurement is carried out on conventional MOS-HEMT devices and the recessed-gate MOS-HEMT devices, the results suggest that the recessed gate MOS devices are of better power characteristics.O₂ plasma treatment is used in this paper to reduce the damage caused by recessed-gate etching. An in-situ oxide-layer is formed during the plasma treatment. After the plasma treatment, schottky barrier height increases and the influence factor decreases. The O2 plasma treatment can improve off-state, sub-threshold characteristic and the breakdown characteristics of recessed gate MOS-HEMT devices.A high-performance GaN recessed gate MOS-HEMT device is reported in this paper with an AlGaN buffer layer and an O2 plasma treatment. The incorporation of an AlGaN buffer into the GaN HEMT significantly improves channel confinement and suppresses the hot-electron effect. The recessed-gate MOS-HEMT with an AlGaN buffer layer has excellent power characteristics and predominant microwave power applications.