Influence of PECVD deposited SiN x passivation layer thickness on In0.18Al0.82N/GaN/Si HEMT

The influence of plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiN x ) passivation film thickness on In0.18Al0.82N/GaN/Si heterostructures and HEMTs has been investigated. The formation of Si3N4 was confirmed by x-ray photoelectron spectroscopy (XPS) measurements. X-ray reflectivity (XRR) measurements reveal that both the density and roughness of the SiN x film increase with increasing film thickness. With an increase in SiN x film thickness, a significant increase in two-dimensional electron gas (2DEG) density, drain current, extrinsic transconductance and negative threshold voltage shift of the In0.18Al0.82/GaN/Si HEMTs are observed. An optimal thickness of SiN x is ~100 nm and it yields a substantial increase in 2DEG density (~30%) with a minimum sheet resistance for In0.18Al0.82N/GaN/Si heterostructures. Furthermore, we correlate the observed SiN x film thickness-dependent electrical characteristics of In0.18Al0.82/GaN/Si HEMTs with the density of the SiN x film.