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 $\mathrm{Al}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ heterostructure field-effect transistors. The two-dimensional electron density $\left(N_s\right)$ 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 $N_s$ , the sheet resistance $\left(R_{\mathrm{sh}}\right)$ significantly decreased after the deposition, and it had low values of $320–460\Omega ∕◻$ for extremely thin AlGaN barriers of $4–10\mathrm{nm}$ . The increase in $N_s$ 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 $R_{\mathrm{sh}}$ . Moreover, we found that Cat-CVD was more effective than plasma-enhanced chemical vapor deposition in increasing $N_s$ . 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.