Microstructural analysis of Ti/Al/Ti/Au ohmic contacts to n-AlGaN/GaN Available to Purchase

To develop high quality AlGaN/GaN heterostructure field effect transistors for use in high power, high frequency, and high temperature applications, low resistance, thermal stable ohmic contacts with good surface morphology are essential. Low specific contact resistances have been achieved using an Au/Ti/Al/Ti contact: a minimum value of $6.33×10−6 Ω cm2$ was attained after annealing at 700 °C for 30 s. Microstructural analysis using transmission electron microscopy indicated that there is significant interaction between the metallization components and the semiconductor during annealing. The optimum electrical properties correspond to a microstructure that consists of $Au2Ti$ and TiAl layers as well as of a thin Ti-rich layer (∼10 nm thick) at the metallization/AlGaN interface. Degradation of the contact occurred for annealing temperatures in excess of 750 °C, and was accompanied by decomposition of the AlGaN layer and formation of a Au–Ti–Al–Ga quaternary phase.