Effects of SiN passivation by catalytic chemical vapor deposition on electrical properties of AlGaN∕GaN heterostructure field-effect transistors

Abstract

We investigated the effects of SiN passivation by catalytic chemical vapor deposition (Cat-CVD) on the electrical properties of AlGaN∕GaN heterostructure field-effect transistors. The two-dimensional electron density (Ns) greatly increased after the Cat-CVD SiN deposition, and the tendency of the increase was enhanced with decreasing AlGaN barrier thickness. As a result of the large increase in Ns, the sheet resistance (Rsh) significantly decreased after the deposition, and it had low values of 320–460Ω∕◻ for extremely thin AlGaN barriers of 4–10nm. The increase in Ns showed little dependence on SiN thickness, indicating that the stress applied to the AlGaN barrier by SiN cannot be the origin of the increase. Cat-CVD SiN also improved the in-plane uniformity of mobility for extremely thin-barrier structures, which in turn improved the uniformity of Rsh. Moreover, we found that Cat-CVD was more effective than plasma-enhanced chemical vapor deposition in increasing Ns. A comparison of theoretical calculations and experimental results indicated that these behaviors can be explained by a decrease in the AlGaN surface barrier height due to the SiN deposition.