A flexible
nitride p-n photodiode is demonstrated. The device consists
of a composite nanowire/polymer membrane transferred onto a flexible
substrate. The active element for light sensing is a vertical array
of core/shell p–n junction nanowires containing InGaN/GaN quantum
wells grown by MOVPE. Electron/hole generation and transport in core/shell
nanowires are modeled within nonequilibrium Green function formalism
showing a good agreement with experimental results. Fully flexible
transparent contacts based on a silver nanowire network are used for
device fabrication, which allows bending the detector to a few millimeter
curvature radius without damage. The detector shows a photoresponse
at wavelengths shorter than 430 nm with a peak responsivity of 0.096
A/W at 370 nm under zero bias. The operation speed for a 0.3 ×
0.3 cm2 detector patch was tested between 4 Hz and 2 kHz.
The −3 dB cutoff was found to be ∼35 Hz, which is faster
than the operation speed for typical photoconductive detectors and
which is compatible with UV monitoring applications.
We
demonstrate green emission from InGaN/GaN multiple quantum wells
(MQWs) grown on m-plane sidewalls of GaN wires. To
tune the emission wavelength, InGaN radial wells were grown by metal–organic
vapor phase epitaxy (MOVPE) at decreasing temperatures ranging from
710 down to 620 °C to increase the In incorporation. A comprehensive
investigation combining structural and optical analyses demonstrates
that the green emission from the nonpolar m-plane
wire sidewalls is achieved for the wells grown at 650 °C (namely,
for 2.7 nm thick wells sandwiched by 11 nm thick GaN barriers). The
observed emission wavelength of 500–550 nm is consistent with
an average In-content of MQWs measured in the range of 24 ± 4%
by energy dispersive X-ray (EDX) and atom probe tomography (APT).
Single wires were electrically contacted and the green electroluminescence
from m-plane facets was established on single wire-LED
devices. This demonstrates the possibility to produce green emitters
with core–shell wire LEDs elaborated by industrial and scalable
MOVPE technique.
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