Low-temperature treatment of Al/Ti nanolayers to form solid solution in order to improve the ohmic contacts process formation

Heat treatment of the Al, Al/Ti and Au/Ni/Al/Ti nanolayers at 450 degrees C was studied by measuring transparency, resistivity and also by SIMS (secondary ion mass spectrometry) and XPS (X-ray photoelectron spectroscopy). Heat treatment has led to the increase in transparency and in resistivity of Al/Ti films. On the contrary, the same treatment for the pure Al layer decreases resistivity but transparency increases due to the decrease in the unoxidized Al thickness. The upper Au/Ni layer has led to greater changes in resistivity and transparency but presumably due to a higher oxidation degree, that confirmed by XPS. Observed changes of the Al/Ti layer structure are assumed to be explained not only by oxidation, but also by the partial formation of a Ti-Al solid solution, confirmed by SIMS (Ti and Al redistribution in the layer). The suppression of oxidation, Ti-Al formation temperature reduction and, as a result, possibility to improve GaN HEMT ohmic contacts with such layers were studied.