In situelectronic probing of semiconducting nanowires in an electron microscope

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For the development of electronic nanoscale structures, feedback on its electronic properties is crucial, but challenging. Here, we present a comparison of various in situ methods for electronically probing single, p-doped GaAs nanowires inside a scanning electron microscope. The methods used include (i) directly probing individual as-grown nanowires with a sharp nano-manipulator, (ii) contacting dispersed nanowires with two metal contacts and (iii) contacting dispersed nanowires with four metal contacts. For the last two cases, we compare the results obtained using conventional ex situ litho-graphy contacting techniques and by in situ, direct-write electron beam induced deposition of a metal (Pt). The comparison shows that 2-probe measurements gives consistent results also with contacts made by electron beam induced deposition, but that for 4-probe, stray deposition can be a problem for shorter nanowires. This comparative study demonstrates that the preferred in situ method depends on the required throughput and reliability.

Lay description

In this study, small robots equipped with fine-tipped contacting arms were used within a scanning electron microscope (SEM) to measure the electrical properties of semiconductor nanowires. Semiconductor nanowires are thin rods or needles (diameter one thousandth that of a human hair) and attractive for future opto-electronic devices like solar cells, LEDs, lasers. To develop and optimize them for these applications, we need to be able to measure their electronic properties, which can be challenging given the small scale of the nanowires. For that purpose the miniature robots were combined with techniques to directly write metallic contacts with the electron beam inside the SEM. Alternatively, the tip of the nanowires can be contacted directly by the sharp robot arms. The different measuring techniques were then compared for speed and reliability.

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