AlGaN/GaN Enhancement-Mode MOSHEMTs Utilizing Hybrid Gate-Recessed Structure and Ferroelectric Charge Trapping/Storage Stacked LiNbO3/HfO2/Al2O3 Structure

The hybrid gate-recessed structure and ferroelectric charge trapping/storage stacked structure were used in AlGaN/GaN enhancement-mode metal-oxide-semiconductor high-electron mobility transistors (E-MOSHEMTs). The stacked structure consisted of a bottom 10-nm-thick Al 2 O 3 tunnel oxide layer, a middle 4-nm-thick HfO 2 charge trapping/storage layer, and a top 40-nm-thick LiNbO 3 ferroelectric blocking layer. Using the postannealing process, a high polarized C + domain of the pulsed laser-deposited LiNbO 3 ferroelectric blocking layer was formed and the interface quality of the stacked structure was improved simultaneously. Consequently, positive threshold voltage for enhancement-mode operation was obtained. By studying the performances of the resulting devices, it was found that enhancement-mode behaviors were observed for initializing gate more than 5 V, and the threshold voltage of 1.6 V was obtained for initializing gate at 12 V. The high-frequency performances of the extrinsic unit gain cutoff frequency of 5.9 GHz and maximum oscillation frequency of 10.1 GHz were obtained. Furthermore, a low normalized noise power density of about 1.9\times 10^{-14} Hz −1 was achieved for the devices operating at a frequency of 10 Hz, a gate-source voltage of 5 V, and a drain-source voltage of 1 V.