Devising a recipe to synthesize indium antimonide single-nanowire field effect transistors with OHMIC contacts Lam, Rudy; Lee, Shaun (Won Sug)
The goal of this project was to deliver functional nanowire FETs made with Indium Antimonide nanowires to our sponsor Dr. Mario Beaudoin. To create nanowire FETs, first we created a grid of Ti/Au bonding pads on an oxidized silicon wafer using photolithography. InSb nanowires, provided by our sponsor, was then deposited onto the grid, after which they were mapped using scanning electron microscope. Lengthy ( ~10 μm ), un-clumped nanowires were chosen and then Ti/Au contact lines between nanowires and their nearest bonding pads were drawn using electron-beam lithography. The final step was performing a Voltage-current measurement on the nanowire FETs in order to examine whether the nanowires made ohmic contacts with the contact lines. The measurement results showed that our method of fabrication accurately produced functional contact lines at desired locations; however the results were regrettably inconclusive in revealing whether the contacts were ohmic. The two possible reasons for the inconclusive results were low break-down voltage of the nanowires (~10 milli-volts) and insufficient resolution of the probe station. Due to the nanowires’ high resistance (~106 ohm), the maximum current allowed before the break-down of the nanowires was in the order of nano-amperes, which was the limit of the current source’s resolution. Therefore, resulting voltage-current curve showed an atypical behavior that does not correspond to either ohmic or non-ohmic contacts. After discussion with the project sponsor, it was decided to end the project at this point since a probe station with sufficient resolution was not available. More meaningful voltage-current curve might be observed in a low-temperature measurement as the resistance of the nanowires decreases significantly at a very low temperature, but such measurement was outside the scope of this project. For future projects, we have a few recommendations that could improve the synthesis process. First, a new set of more-closely-spaced alignment markers should be introduced in order to accommodate smaller nanowires because much time had to be spent finding sufficiently big nanowires that can work with the current pattern. Also, by beginning the training session sooner and making it more customized and structured for this project, the time required to produce first successful nanowire FETs can be shortened.
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