We have characterized the photodetection capabilities of single GaN nanowires
incorporating 20 periods of AlN/GaN:Ge axial heterostructures enveloped in an
AlN shell. Transmission electron microscopy confirms the absence of an
additional GaN shell around the heterostructures. In the absence of a surface
conduction channel, the incorporation of the heterostructure leads to a
decrease of the dark current and an increase of the photosensitivity. A
significant dispersion in the magnitude of dark currents for different single
nanowires is attributed to the coalescence of nanowires with displaced
nanodisks, reducing the effective length of the heterostructure. A larger
number of active nanodisks and AlN barriers in the current path results in
lower dark current and higher photosensitivity, and improves the sensitivity of
the nanowire to variations in the illumination intensity (improved linearity).
Additionally, we observe a persistence of the photocurrent, which is attributed
to a change of the resistance of the overall structure, particularly the GaN
stem and cap sections. In consequence, the time response is rather independent
of the dark current.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters (2016),
copyright (C) American Chemical Society after peer review. To access the
final edited and published work see
http://dx.doi.org/10.1021/acs.nanolett.6b0080
