Low-Frequency Noise in Enhancement-Mode GaN MOS-HEMTs by Using Stacked $\hbox {Al}_{2}\hbox {O}_{3}/\hbox {Ga}_{2}\hbox {O}_{3}/\hbox {Gd}_{2}\hbox {O}_{3}$ Gate Dielect

In this letter, enhancement-mode AlGaN/GaN metal-oxide semiconductor high-electron-mobility transistors (HEMT) (MOS-HEMTs) are realized by using N₂O plasma oxidation and Gd₂O₃ stacked-gate dielectric technologies. Before the gate metal was deposited, the AlGaN barrier layer was treated by 150-W N₂O plasma for 200 s to remove the AlGaN native oxide layer and, simultaneously, to form Al₂O₃/ Ga₂O₃ compound insulator. Then, a 10-nm-thick high-dielectric-constant Gd₂O₃ thin film was electron-beam evaporated as a stacked-gate dielectric. To elucidate the interface phenomena of the device, the dependence of the 1/f noise spectra on the gate bias was studied. The fluctuation that is caused by trapping/detrapping of free channel carriers near the gate interface can be reduced by N₂O plasma treatment. Additionally, the variation of the Hooge factor (αH) of a traditional metal gate GaN HEMT, measured at 77 K and 300 K, is huge, particularly in the subthreshold gate voltage regime. The tunneling leakage current that is induced by the interface traps is determined to be higher than that in the MOS-HEMT design. The threshold voltage (V_th) of depletion-mode GaN HEMT was -3.15 V, and this value can be shifted to +0.6 using N₂O-treated stacked-gate AlGaN/GaN MOS-HEMTs.