Porous silicon nanowires fabricated by electrochemical and laser-induced etching

Electrochemical and laser-induced etching processes were simultaneously used to synthesize the nanowires structure of porous silicon (PS). Surface morphology and structural properties of nanostructured silicon were characterized by using scanning electron microscopy (SEM) and atomic forces microscopy (AFM) images. Nanowires with dimensions of few nanometers were formed on the whole etched surface. The optical properties of silicon nanostructures were studied. Raman spectra were shifted and broadened relatively to 519.9 cm⁻¹ of PS prepared by electrochemical etching, and shifted to 517.2 cm⁻¹ for laser-induced etching process and to 508.9 cm⁻¹ for electrochemical and laser etching simultaneously. Blue shift luminescence was observed at 649.6 nm for PS produced by electrochemical etching, and at 629.5 nm for laser-induced etching. PS produced a blue shift at 626.5 nm using both etching procedures simultaneously. X-Ray diffraction (XRD) was used to investigate the crystallites size of the PS as well as to provide an estimate of the degree of crystallinty of the etched sample.     

Porous GaN on Si(1 1 1) and its application to hydrogen gas sensor

The growth of heterostructure of n-type GaN/AlN/Si(1 1 1) is carried out using the molecular beam epitaxy (MBE) Veeco model Gen II system. The surface morphology of the as-grown GaN sample showed pits on the GaN surface in a ratio small than those found by other research groups. Porous GaN samples were synthesized by an electrochemical etching technique combined with increasing the current density to 75 mA/cm². The formation of pore structures are of different sizes, the etched surface became hexagonal, and pore structures are confined to a smaller size. The PL results showed greater blue shift luminescence in comparison to results found by other research groups. The reduction in crystallite size is confirmed by an increase in the broadening of XRD spectra. Raman spectra also displayed a strong band at 522 cm⁻¹ from the Si(1 1 1) substrate, and a small band at 301 cm⁻¹. These are due to the acoustic phonons of Si. Two Raman active optical phonons are assigned to h-GaN at 139 cm⁻¹ and 568 cm⁻¹, due to E2 (low) and E2 (high) respectively. The sensitivity of the gas sensor is increased as a function of the hydrogen flow rate and they became much higher compared to the as-grown sample.     

Nanostructured GaN on silicon fabricated by electrochemical and laser-induced etching

Nanostructured GaN layers have been fabricated by electrochemical and laser-induced etching (LIE) processes based on n-type GaN thin films grown on the Si (111) substrate with AlN buffer layers. The effect of varying current and laser power density on the morphology of the GaN layers is investigated. The etched samples exhibited a dramatic increase in photoluminescence intensity as compared to the as grown samples. The average diameter of the GaN crystallites was about 7-10 nm, as determined from the PL data The Raman spectra also displayed stronger intensity peaks, which were shifted and broadened as a function of etching parameters. A strong band at 522 cm^− 1 is from the Si (111) substrate, and a small band at 301 cm^− 1, due to the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 cm^− 1 and 568 cm^− 1due to E2 (low) and E2 (high) respectively.     

Thickness effect of Al2O3 as buffer layer on Alq3 sensitivity for toxic gas

Gas sensitivity improved and becomes more stable when a buffer layer (Al₂O₃) inserted between the active layer (Alq₃) and glass substrate. In this paper, we introduce a device (Au/Alq₃/Al₂O₃) exposure to NO₂ gas to enhancement the role of Alq₃ in organic gas sensor. We employed the pulsed laser deposition technique to grow Al₂O₃ films with different thicknesses of 50, 75, and 100 nm on glass substrates. The structural and optical properties of the buffer layer were studied. XRD pattern shows that all films are polycrystalline in nature, and the mean crystallite size decreases when buffer layer thickness increase, insert the buffer layer did not change the direction of crystalline growth for the dominant planes of Alq₃. The high resolution FE-SEM images for buffer layers indicates that the large crystals collect in the form of nanotubes, and changed into spherical shapes and flakes-like shapes, with increased thickness of Al₂O₃. The atomic force microscopy technique uncovered the uniform and dense distribution of nano crystallized. The band gap energy is ~3.8 and increased with increase a buffer layer. PL spectra of Alq₃/Al₂O₃ samples exhibits a distinctive green emission at around 535 nm for pure Alq₃, and blue shifting occurs toward the low wavelengths with increase thickness of Al₂O₃. More effect of Al₂O₃ was appeared when added to Alq₃; this is appeared by the effect of shifting energy gap behavior, grain size on the sensor properties. The sensitivity, and response time with increase thickness of buffer layer is improved.     

Laser-induced etching parameters impact on optical properties of the silicon nanostructures

Porous silicon (PS) was fabricated by laser-induced etching (LIE) process. The objective of this study is to investigate the selected LIE parameters to control size and shape of nanostructures,which are considered important factors in semiconductor device applications. Photoluminescence output intensity becomes stronger due to the increase in the number of emitted photons on the porous surface. There is a dramatic increase in photoluminescence intensity due to the increase of porosity as a function of laser...