Investigation of different buffer layer impact on AlN/GaN/AlGaN HEMT using silicon carbide substrate for high-speed RF applications

Abstract

The AlN/GaN heterostructure on the AlGaN back barrier with different buffer layer structures using a silicon carbide (SiC) substrate was investigated in this work. This study mainly focused on selecting a cost-effective buffer layer with a thickness of more than 1 μm and fewer defects for improving DC/RF performance. The extra epitaxial growth process steps can be avoided by choosing an appropriate, high-quality buffer material called β-Ga2O3 (β-gallium oxide). It has a good lattice match with AlGaN alloys and SiC. It leads to fabricating cost-effective, reliable HEMTs. The GaN buffer has a poor lattice match with SiC; the nucleation layer must be used between GaN and SiC for lattice match to avoid stress defects and dislocations, which helps to reduce buffer traps. The growth of thick GaN crystals leads to high costs and more defects. Creating a solid conduction band barrier with the help of a back-barrier (AlGaN) leads to a boost in the confinement of electrons in both devices. Still, the traps and defects in the GaN buffer do not effectively halt the leakage current compared to the β-Ga2O3 buffer. The T-shaped gate with the impact of LGD (gate to drain length) and LGS (gate to source length) scaling in lateral dimensions was also studied and the device performance was reported. The HEMT with β-Ga2O3 buffer delivers significant results in drain current (2.3 A/mm), transconductance (603 S/mm), and cut-off frequency (486 GHz) for the scaled lateral lengths LG (Gate Length) of 60 nm,LGD of 0.9 μm, and LGS of 0.4 μm. This excellent performance helps to use this HEMT device in cost-effective future high-speed RF applications.