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The electrical, thermal, and microstructural characteristics of Ti/Al/Ti/Au ͑30 nm/100 nm/30 nm/30 nm͒ multilayer Ohmic contacts to n-GaN ͑doping level 5ϫ10 17 cm Ϫ3) were studied. The lowest contact resistivity derived from the annealed contact was S ϭ3.0ϫ10 Ϫ6 ⍀ cm 2. The contacts were robust and showed high-thermal stability. X-ray diffraction and Auger electron spectroscopy studies were made to investigate the microstructure of the annealed contacts. The key to the success of the contact was the Ti layers placed on both sides of the Al layer. Upon annealing, there occurred both in-diffusion and out-diffusion of the Ti layer in intimate contact with the GaN film. The in-diffusion of this led to the formation of TiN, while the out-diffusion of this led to the formation of Ti-Al alloys. The second Ti layer also in-diffused and out-diffused during annealing. However, due to the presence of Au, the out-diffusion was marginalized, and the in-diffusion was higher than the out-diffusion. The in-diffusion led to the formation of Ti-Al alloys with the remaining Al content. Consequently, both the Al and the Ti ͑from the second Ti layer͒ contents were almost fully consumed, and none of them were left to appear on the contact surface to form oxides.

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Epitaxial films of La2/3Ca1/3MnO3 were successively implanted with 100 and 200 keV silver ions at fluences of 4.5×1015 and 1×1016 ions/cm2, respectively, to achieve a fairly uniform implant distribution. The as-implanted films are insulating and do not show a metal–insulator transition. Postimplantation annealing at 950 °C shows a recovery of the high structural quality of the films, along with an increase in the metal–insulator transition temperature (Tp), magnetoresistance, and the peak temperature coefficient of resistance (TCR) at the transition. The peak TCR of 23% for manganite films is clearly significant for bolometric applications.