This
work uniquely reports the synthesis of Zn
x
Mg
1–
x
O nanowires and submicron
columns by utilizing a traditional carbothermal reduction process
toward forming ZnO nanowire ultraviolet detectors, while simultaneously
utilizing Mg
3
N
2
as the source of Mg. To investigate
the relationship between Mg content in the ZnO lattice and the cutoff
wavelength for high spectral responsivity, the nanowires were annealed
in a series of designed conditions, whereas chemical, nanostructural,
and optoelectronic characteristics were compared before and after
treatment. Postanneal scanning electron micrographs revealed a reduction
of the average ensemble nanowire dimensions, which was correlated
to the modification of ZnO lattice parameters stemming from Zn
2+
dissociation and Mg
2+
substitution (confirmed
via Raman spectroscopy). The analysis of cathodoluminescence spectra
revealed a blueshift of the peak alloy band-edge emission along with
a redshift of the ZnO band-edge emission; and both were found to be
strong functions of the annealing temperature. The conversion of Zn
2
SiO
4
to Mg
2
SiO
4
(in O
2
) and MgSiO
3
(in Ar) was found to correspond to
transformations (shifting and scaling) of high-energy luminescence
peaks and was confirmed with X-ray diffraction analysis. The tunability
of the cutoff photodetection wavelength was evaluated as the nanowire
arrays exhibited selective absorption by retaining elevated conduction
under high-energy UV-C irradiation after thermal treatment but exhibiting
suppressed conductivity and a single order of magnitude reduction
in both spectral responsivity (
R
λ
) and photoconductive gain (
G
) under UV-A illumination.
Noise analysis revealed that the variation of detectivity (
D
*) depended on the regime of ultraviolet irradiation, and
that these variations are related to thermal noise resulting from
oxygen-related defects on both nanowire and substrate surfaces. These
results suggest a minor design tradeoff between the noise characteristics
of thermally treated ZnMgO nanowire array UV detectors and the tunability
of their spectral sensitivity.
SiGeSn is a promising group IV material to develop the field of silicon photonics. Increasing the tin concentration in the alloy is desired in order to achieve a direct bandgap in the material. This necessitates low temperature growth and proper strain management in the films during growth to prevent tin segregation. In this work, plasma enhanced chemical vapor deposition (PECVD) was used to grow composition graded SiGeSn films at low processing temperatures of 350 °C-380 °C using a simplified PECVD reactor. Polycrystalline films were deposited using a multi-step approach to prevent tin phase separation at higher Sn concentrations by alleviating the strain arising from the incorporation of Sn in the film lattice. Rutherford Back Scattering measurements indicated that films with Sn content of up to 8% without any Sn phase segregation were achieved. The structural and optical properties of the films were analyzed using X-ray diffraction and Raman spectroscopy.
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