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

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 degrees C. The drain current density and transconductance increase greatly after post-gate-annealing (PGA, 400 degrees C, 5 min) treatment. The V-th of the MIS-HEMT decreases after PGA treatment and the C-V characteristics are a good match to the V-th 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 V-th 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.