Engineering a Unified Dielectric Solution for AlGaN/GaN MOS-HFET Gate and Access Regions

Typically GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) have used two separate dielectrics for the gate and access regions. However, as this article shows, with proper gate-stack engineering, a unified dielectric solution can be achieved for the transistor. HfO
₂
dielectrics were deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H
₂
O) and ozone (O
₃
). It was found that MOS-HFETs with O
₃
oxidant yielded lower threshold voltage (VTH) shifts, higher maximum drain current (IDS,max) of 340 mA/mm, 20% lower ON-resistance (RON), higher peak transconductance at 112.66 mS/mm, lower hysteresis, and lower gate leakage (5.4 × 10
^-6
A/cm
²
) compared to water oxidant based MOS-HFETs with IDS,max of 240 mA/mm, 81.38 mS/mm peak transconductance, and 1.7 × 10
^-4
A/cm
²
gate leakage. DC/RF dispersion tests showed MOS-HFETs with O
₃
oxidant had -200x better current collapse recovery. Temperature characterization and reliability test results, such as high-temperature reverse bias (HTRB), are published for the first time on ALD-HfO
₂
/AlGaN/GaN MOSHFETs using tetrakis(dimethylamino)hafnium (TDMAH) and O
₃
precursor. Using an ozone oxidant provided more stability (i.e., less variability in RON and VTH) as a function of temperature. Finally, when devices were electrically stressed in the OFF-state, the HTRB test showed minimal VTH drift (<; 0.5 V) in the case of O
₃
oxidant versus much larger VTH drift (2.5 V) in the case of H
₂
O oxidant.