Comparative Study of Characteristics and Interface States with and without Post‐Gate‐Annealing Treatment for AlGaN/GaN‐Recessed Metal–Insulator–Semiconductor High Electron Mobility Transistors Using HfO₂ Gate Insulator on Si Substrates

Abstract

Three types of enhancement‐mode (E‐mode) AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS‐HEMTs) with different barrier depths are fabricated on Si substrates. A HfO2 gate insulator with a thickness of 30 nm is grown by plasma‐enhanced atomic layer deposition (PEALD) at 300 °C. The drain current density and transconductance increase greatly after post‐gate‐annealing (PGA, 400 °C, 5 min) treatment. The Vth of the MIS‐HEMT decreases after PGA treatment and the C–V characteristics are a good match to the Vth change of the transfer characteristics. The interface states are in the form of trap states and fixed charges. The trap states at the HfO2/AlGaN interface are measured by the frequency‐ and voltage‐dependent conductivity method. The trap state density and time constant decrease after the PGA treatment. The fixed charge density can be calculated by the Vth shift. According to the calculation results, the fixed charge density also decreases. The PGA treatment can reduce the interface state density effectively and is a significant process for the gate‐recessed MIS‐HEMT.

Comparative study on characteristics of Si-based AlGaN/GaN recessed MIS-HEMTs with HfO2 and Al2O3 gate insulators*

“…[20] The electrons in the channel reach the dielectric/AlGaN interface when the gate voltage increases, so the gate capacitance increases due to the series connection of the dielectric layer capacitance and barrier layer capacitance to the only dielectric layer capacitance. [15] For the MIS-HEMT with 3-nm and 0-nm barriers, the second slope is observed in none of the C-V curves. As the barrier layer is too thin, the electrons reach the dielectric/AlGaN interface directly.…”

“…For the MIS-HEMT with HfO 2 , The drain current density and transconductance increase greatly after post-gateannealing (PGA, 400 • C, 5 min) treatment. [15] The threshold voltage (V th ) of the MIS-HEMT decreases after the PGA treatment. Figure 6 shows the comparisons of transfer characteristics between the HfO 2 and Al 2 O 3 MIS-HEMTs with different etching depths after the PGA treatment.…”

“…The interface state density can be reduced effectively by filling the nitrogen vacancies through oxygen atoms into the HfO 2 and Al 2 O 3 layer and reducing oxygenrelated defects at the dielectric/AlGaN interface. [15] It can be concluded that the interface states under the gate greatly influence the current collapse.…”

“…Finally, post gate annealing (PGA) treatment of 400 • C in ambient N 2 for 5 min was implemented for reducing the interface state density. [15] The L g , L gd , and L ds of the devices were 1.0 µm, 3.5 µm, and 7.0 µm, respectively. The W g of the device was 50 µm.…”

Positive Shifting of Vth with Enhanced DC Performance in AlGaN/GaN Schottky-Gate HEMT through Optimized UV/O3 Treated Gate Interface and Thermal Engineering

“…The decreased of trap states means the reduction of nitrogen vacancies by PMA process with N 2 gas and due to diffusion of gate metal. 8,33 Moreover, previous studies also mentioned that the PMA could effectively reduce shallow traps by the creation of deep traps, which subsequently reduces the interface state density. 34 In addition, the C-V characteristics of the conventional HEMT with and without PMA treatment is shown in the inset of Fig.…”