We fabricated a gas sensor with a wide-bandgap ZnGa2O4 (ZGO) epilayer grown on a sapphire substrate by metalorganic chemical vapor deposition. The ZGO presented (111), (222) and (333) phases demonstrated by an X-ray diffraction system. The related material characteristics were also measured by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. This ZGO gas sensor was used to detect nitric oxide (NO) in the parts-per-billion range. In this study, the structure effect on the response of the NO gas sensor was studied by altering the sensor dimensions. Two approaches were adopted to prove the dimension effect on the sensing mechanism. In the first approach, the sensing area of the sensors was kept constant while both channel length (L) and width (W) were varied with designed dimensions (L × W) of 60 × 200, 80 × 150, and 120 ×100 μm2. In the second, the dimensions of the sensing area were altered (60, 40, and 20 μm) with W kept constant. The performance of the sensors was studied with varying gas concentrations in the range of 500 ppb~10 ppm. The sensor with dimensions of 20 × 200 μm2 exhibited a high response of 11.647 in 10 ppm, and 1.05 in 10 ppb for NO gas. The sensor with a longer width and shorter channel length exhibited the best response. The sensing mechanism was provided to explain the above phenomena. Furthermore, the reaction between NO and the sensor surface was simulated by O exposure of the ZGO surface in air and calculated by first principles.
Al0.12GaN/GaN membrane-type photodetectors
(M-PD) were
separated from the Si substrates through a chemical lift-off process.
High photocurrent, low dark current, and high responsivity properties
were observed in the M-PD structure compared to that on the Si substrate.
Lattice-mismatch-induced tensile strain on the Al0.12GaN
layer was enlarged in the M-PD structure and was analyzed by the photoluminescence
and Raman spectra. From the simulation results, the energy band bending
induced the potential barrier height at the AlN/air separated surface
to deplete the surface states and suppress the leakage current. The
strain in the AlGaN/GaN structures was manipulated by removing the
Si substrate and roughening the AlN surface. The membrane-type ultraviolet
photodetector consisted of the AlGaN/GaN two-dimensional electron
gas channel and the large tensile strain at the Al0.12GaN
layer, which can be used for high-efficiency optoelectronic applications.
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