Characterization of Al2O3 /GaN/AlGaN/GaN metalinsulator-semiconductor high electron mobility transistors with different gate recess depths

In this paper,in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs),we demonstrate better performances of recessed-gate Al 2 O 3 MIS-HEMTs which are fabricated by Fluorine-based Si 3 N 4 etching and chlorinebased AlGaN etching with three etching times (15 s,17 s and 19 s).The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT.Through the recessed-gate etching,the transconductance increases effectively.When the recessed-gate depth is 1.02 nm,the best interface performance with τ it =(0.20-1.59) μs and D it =(0.55-1.08)×10 12 cm 2 ·eV 1 can be obtained.After chlorine-based etching,the interface trap density reduces considerably without generating any new type of trap.The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices.By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times,it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively.     

High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current (DC) and pulsed measurements are performed to determine the degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas (2DEG). The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.     

Enhancement-mode AlGaN/GaN high electronic mobility transistors with thin barrier

An enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMTs) was fabricated with 15-nm AlGaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around --1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs (--3.5 V). Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-μ m gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/mm, respectively. Compared with the 22-nm barrier E-mode devices, V_T of the thin barrier HEMTs is much more stable under the gate step-stress.