AlGaN/GaN ohmic contact resistance variations across epitaxial suppliers

摘要

Six AlGaN/GaN epitaxy suppliers grew their standard films on SiC substrates as deliverables for Defense Advanced Research Projects Agency's (DARPA's) "Wide Bandgap Technology Initiative". An ohmic contact study was performed to determine an optimum process for each supplier and to study the impact of growth conditions on contact resistance. On each wafer four metal stacks were evaporated, with one being the epitaxial supplier's proprietary stack. The wafers were diced and alloyed using AFRL's standard conditions and the epitaxial supplier's condition. The optimal metal stack was found for each wafer and yielded contact resistances lower than 1 Ω mm. However, each wafer required a different metal stack in order to achieve the lowest contact resistance, which indicates that growth conditions can have a large impact on ohmic contact results. The molybdenum (Mo) based ohmic contacts showed little variation from sample to sample and produced marginally acceptable ohmic contact values across all material suppliers. The Mo based contacts show potential for optimization as a generic ohmic contact that is not dependent on the growth conditions of the material.