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 (N-s) 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 (R-sh) significantly decreased after the deposition, and it had low values of 320-460 ohm/square for extremely thin AlGaN barriers of 4 - 10 nm. 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. (c) 2006 American Institute of Physics.
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