Multi-Probe Electrical Characterization of Nanowires for Solar Energy Conversion

Catalysis-assisted vapor-liquid-solid nanowire (NW) growth offers opportunities to prepare versatile, axial, and radial III-V homo- and hetero-structures, which combine multiple scientific and economic benefits including applications in innovative solar energy conversion. For an essential and suitable optoelectronic analysis of NW heterocontacts, we have established a sophisticated multi-tip scanning tunneling microscope (STM) used as a four-point prober, which is in vacuo combined with state-of-the-art preparation, enabling an individual characterization of free-standing NWs with no contamination after preparation and with highest spatial resolution. We apply the superior capabilities of the ultra-high-vacuum-based multi-tip STM to perform an indepth study of gallium arsenide NW structures, incorporating an axial p-n junction. Two- and four-point I-V characteristics of the diode are recorded non-destructively, enabling the determination of a local ideality factor. Four-point-probe measurements at different NW positions result in an axial resistance profile, allowing the calculation of the doping concentration of p- and n-doped parts. Around the p-n junction, a 500-nm-width region of low conductance was detected, indicating a compensation effect of dopants during growth. By recording electron-beam-induced current images, the position of the charge separating contact was confirmed.