Investigation of MBE grown high Al concentration AlGaN ohmic contact

Achieving low resistance ohmic connections is one of the significant factors in improving the performance of optoelectric and semiconductor devices. In this work, we examined the decrease in specific contact resistance (ρc) after high-temperature annealing and vanadium thickness variation on an n-type AlGaN epitaxial layer with a high aluminum concentration (75%). To measure it, we prepared rectangular transmission line model electrodes and measured the specific contact resistance at annealing temperatures ranging between 800 and 950 °C. The results showed that the minimum specific contact resistance achieved was 4.12 × 10−2 Ω cm2 at an annealing temperature of 850 °C, which was two times lower compared to that of surface contact mode. It is also demonstrated how the contact resistance of the epitaxial n-type AlGaN layer varies as the vanadium thickness changes from 2 to 15 nm.