Mechanisms of a Rectifying TiN Gate Contact for AlGaN$/$GaN HEMTs on Silicon Substrate

Abstract

Rectifying Titanium Nitride (TiN) gate contact technology is developed for AlGaN $/$ GaN based micro and nanometer HEMTs. A high compressive strain occurring in thinner TiN films (ranging from 5 nm to 60 nm), deposited by sputtering, leads to a reduction in tensile strain at the surface of AlGaN barrier. The diminution in tensile strain forms a pseudo- $p$ -type layer (diode-like). This strain reduction has no effect on the bandgap of the AlGaN barrier layer, allowing the gate to withstand a reverse gate bias larger than 100 V. Characterization using the high-resolution transmission electron microscopy combined with the X-ray photoelectron spectroscopy reveals a good TiN $/$ AlGaN interface quality and no diffusion of TiN into AlGaN. The effective energy barrier of the rectifying nanoscale TiN gate contact has a relatively large height of 1.1 eV associated with an ideality factor of 1.4. A dramatic drop of the reverse-bias leakage current down to 11 pA $/$ mm is measured at −30 V. In addition, electrical measurements show very low gate and drain lag effects of 4.2 ${\%}$ and 6.7 ${\%}$ , respectively.