The effects of different rapid thermal annealing times on ohmic contacts to the AlGaN/GaN HEMT structure

초록

This work uses Ti/Al/Ni/Au metal-stack scheme for obtaining low resistance ohmic contacts to AlGaN/GaN high-electron mobility (HEMT) structures with different rapid thermal annealing (RTA) times at specific temperatures. The specific contact resistance (rho sc) of ohmic contact is determined using a transfer length model (TLM) through the analysis of current-voltage (I-V) characteristics. Measured samples were exhibited with linear characteristics regardless of RTA duration. The sample annealed at 850 degrees C for 60 s showing the low specific contact resistance of rho sc= 3.23 x 10-7 (+/- 8.07 x 10-8) ohm & sdot;cm2 and contact resistance of 0.13 (+/- 0.01) Omega & sdot;mm, respectively. Based on interfacial product results (i.e., X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM)), there are Al-rich and TiN-metal-alloyed phases formed at the metal-stack and AlGaN films with an increase in RTA time at nitrogen (N2) ambient, which gives a significant concentration of nitrogen vacancies. These increase in nitrogen vacancies may result in significant n-doping, hence facilitating low contact resistivity.

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