Control of Buffer-Induced Current Collapse in AlGaN/GaN HEMTs Using SiN_x Deposition

The stoichiometry of low-pressure chemical vapor deposition SiN_x surface passivation is shown to change vertical conductivity at the top of the epitaxial stack in GaN-on-Si power high-electron mobility transistors (HEMTs). This changes the charge stored in the carbon-doped GaN layer during high-voltage operation, and allows direct control of buffer-related current collapse in HEMTs. Substrate bias ramps are used to identify the changes in C:GaN charge trapping and vertical leakage. Channel length dependence indicates a lateral conductivity in the C:GaN with a localized increase in vertical conductivity under the ohmic contacts. An optimum SiN_x recipe is identified which simultaneously delivers low current collapse and low drain leakage.