We studied the influences of the thickness of the porous silicon layer and the conductivity type on the porous silicon sensors response when exposed to ethanol vapor. The response was determined at room temperature (27 ∘C) in darkness using a horizontal aluminum electrode pattern. The results indicated that the intensity of the response can be directly or inversely proportional to the thickness of the porous layer depending on the conductivity type of the semiconductor material. The response of the porous sensors was similar to the metal oxide sensors. The results can be used to appropriately select the conductivity of semiconductor materials and the thickness of the porous layer for the target gas.
The study of GaN morphology and structure modification due to the variation of the nitridation temperature are reported. GaN is obtained by nitridation of GaAs (1 1 1) using the flow of a mixture of hydrogen and ammonia into a horizontal CVD system. The experiments are carried out at atmospheric pressures of 800, 900, and 1000°C for 1 h. XRD results together with the pole figure indicate that GaN (1-x) As x is obtained at 800°C, that zinc-blende GaN structure is obtained at 900°C, and that wurtzite GaN structure is obtained at 900°C. The photoluminescence emission peak (obtained at room temperature) shifts to 420, 384, and 372 nm with the nitridation temperature change, in agreement with the XRD and pole figure results. SEM images show the morphology change, where GaN (1−x) As x and GaN layers are obtained at 800 and 900°C, respectively, while GaN columns are obtained at 1000°C. The morphology and structure change due the nitridation temperature variation are also discussed based on the results.
GaN columns are grown by (1 1 1) GaAs nitridation at 1000 °C. GaAs wafers are used as a substrate and Ga source. The nitridation is performed using a hydrogen and ammonia flow mix into a horizontal chemical vapor deposition (CVD) system at atmospheric pressure. XRD in correlation with pole figure shows that the structure is wurtzite with a (0 0 0 2) preferential plane. The SEM images show the growth of GaN columns with an agglomerate formation on top. EDS results show that the agglomerate is Ga rich, suggesting a self‐induced nucleation growth. The growth mechanism is discussed briefly. The average diameter and length of the columns are around 1.2 and 10 µm, respectively. The method reported here do not use a template or foreign metallic particles catalyst.
The effect of the deposit temperature of zinc oxide (ZnO) doped with nickel (Ni) by hot filament chemical vapor deposition (HFCVD) technique is reported in this work. The technique allows depositing ZnO:Ni in short intervals (1 min). A deposit of undoped ZnO is used as a reference sample. The reference sample was deposited at 500 °C. The ZnO:Ni samples were deposited at 500 °C, 400 °C, 350 °C, and 300 °C. The samples were studied using structural, morphological, and optical characterization techniques. The Ni incorporation to the ZnO lattice was verified by the shift of the X-ray diffraction peaks, the Raman peaks, the band gap, and the photoluminescence measurements. It was found that the deposit temperature affects the structural, morphological, and optical properties of the ZnO:Ni samples too. The structure of the ZnO:Ni samples corresponds to the hexagonal structure. Different microstructures shapes such as spheres, sea urchins, and agglomerate were found in samples; their change is attributed to the deposit temperature variation. The intensity of the photoluminescence of the ZnO:Ni improves concerning the ZnO due to the Ni incorporation, but it decreases as the deposit temperature decreases.
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