Probing the electronic properties of p-doped gallium arsenide nanowires
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Probing the electronic properties of nm-scaled object is a challenge but is required for doping optimalization and using the nm-scaled objects as building blocks in future devices. In the present study, electron beam induced deposition of platinum was used for contacting and creating two-point probes to beryllium-doped gallium arsenide nanowires. Thereby, a metal-semiconductor-metal structure with rectifying metal-semiconductor contact characteristic is formed (i.e. back-to-back Schottky diode). The current-voltage characteristics of this structure were measured with a micromanipulator set-up within the same vacuum chamber. Based on reviewing the currently most accepted back-to-back Schottky diode model, the validity of the model with regard to the present system was evaluated, and an adopted version for the present study developed. The current-voltage curves were then analyzed using a quantitative fitting method for this model in order to extract information about the nanowire doping and resistance. As this is a direct-write deposition technique, relatively few processing steps are needed compared to performing the same process with electron beam litography. In addition to two-point probes, four-point probes using the same approach were attempted, as this would allow for decoupling the contacting specifics and verify the extracted doping estimate. This were however more challenging, due to stray deposits created during processing, but is believed to be a case of optimizing the deposit parameters. The doping level of the nanowires were however successfully extracted using the two-point probe approach, and was found to be equal to the doping level found by a similar two-probe set-up using electron beam litography. This approach could thus allow for developing efficient, accurate routine doping measurements of nanowires.