Zero-bias photocurrents in highly-disordered networks of Ge and Si nanowires

TL;DR

This study demonstrates zero-bias photo-switching in randomly dispersed Ge and Si nanowire networks, showing significant photocurrents under visible light, with Ge nanowires exhibiting higher responses than Si nanowires.

Contribution

First demonstration of zero-bias optoelectronic switching in disordered Ge and Si nanowire networks fabricated with standard CMOS processes.

Findings

Ge nanowires produce higher photocurrents than Si nanowires.

Photocurrent magnitude depends on nanowire material and channel length.

Sparse networks can outperform dense ones when nanowire length matches channel length.

Abstract

Semiconducting nanowire (NW) devices have garnered attention in self-powered electronic and optoelectronic applications. This work explores and exhibits, for the first time for visible light, a clear evidence of the zero-biased optoelectronic switching in randomly dispersed Ge and Si NW networks. The test bench, on which the NWs were dispersed for optoelectronic characterization, was fabricated using standard CMOS fabrication process, and utilized metal contacts with dissimilar work functions - Al and Ni. The randomly dispersed NWs respond to light by exhibiting substantial photocurrents and, most remarkably, demonstrate zero-bias photo-switching. The magnitude of the photocurrent is dependent on the NW material, as well as the channel length. The photocurrent in randomly dispersed GeNWs was found to be higher by orders of magnitude compared to SiNWs. In both of these material systems, when the length of the NWs was comparable to the channel length, the currents in sparse NW networks were found to be higher than that in dense NW networks, which can be explained by considering various possible arrangements of NWs in these devices.