Secondary ion mass spectrometry (SIMS) depth profiling has been applied to the study of the thermal annealing of ohmic contacts for high electron mobility transistors. The metallic stacks (Ti/Al/Ni/Au) were deposited over the Al 0.28Ga0.72N/GaN/sapphire heterostructures and subjected to a rapid thermal annealing (850 °C for 30 s under N2 atmosphere) to improve the contact performance. The surface morphology and the in-depth chemical distribution of the layered contacts were severely modified due to the treatment. These modifications have been analyzed by SIMS depth profiling and scanning electron microscopy-energy-dispersive X-ray microanalysis. The SIMS analysis conditions have been optimized to achieve simultaneously good sensitivity and to avoid ion-induced mixing effects produced by the primary beam sputtering.
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