Porous wide bandgap semiconductors have been widely studied in the last decade due to their unique properties compared to the bulk crystals. GaN received attention from the researchers as an ideal material to fabricate chemical sensing devices due to its excellent properties such as high thermal, mechanical and chemical stabilities, large band gap and high breakdown voltage. In this work, porous GaN was prepared by ultraviolet (UV) assisted electroless chemical etching method. The samples used in this study were commercial n-GaN grown on sapphire (Al2O3) substrates. The samples were initially cleaned in 1:20 NH4OH:H2O, followed by second cleaning in 1:50 HF:H2O and final cleaning in 3:1 HCl: HNO3 and these samples were etched in HF:H2O2:CH3OH under UV illumination for 60 minutes. The structural properties was characterized using Scanning Electron Microscope (SEM). Hydrogen sensor was subsequently fabricated by depositing Pd Schottky contact onto the porous GaN sample. The effect of sensing dilute H2 gas with different concentration which is 1% and 2% H2 in a N2 gas ambient was analyzed. The Schottky barrier height of the gas sensor samples was reduced upon exposure to gas. The porous GaN resulted better sensitivity compared to the as grown GaN sample in H2 gas sensing.
Porous GaN structures were formed from crystalline GaN on conducting AL2O3 substrate using Pt-assisted electroless etching in HF: CH3OH: H2O2 = 1:4:4 under illumination of 500 W UV lamp. Scanning electron microscope (SEM) photoluminescence (PL) and Raman spectra measurements evidenced important features of the pore morphology, nanostructures and optical properties. According to the SEM micrographs, the three-dimensional ridge structure appears with the formation of porous material between the ridges. The porous layer exhibited a substantial PL intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E2(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.
Adsorbents were derived from banana peel through chemical treatment using phosphoric acid, potassium hydroxide, and sodium hydroxide to adsorb methylene blue from water. The adsorption of methylene blue was performed at varying concentrations and contact times. The equilibrium data fitted well with Langmuir equation, with a maximum monolayer adsorption capacity of 99.28 mg/g (28%). Phosphoric acid-treated adsorbent exhibits a greater capacity despite a lower affinity than the other adsorbents. A two-stage batch adsorber model was developed to optimize the adsorbent dosage for performance evaluation. Banana peel is a promising resource of adsorbent for wastewater treatment.
This article presents the studies of Pt Schottky contact on porous n-type GaN for hydrogen sensing. Porous GaN was generated by UV assisted electroless chemical etching. Hydrogen sensor was subsequently fabricated by depositing Pt Schottky contacts onto the porous GaN sample. For comparative study; a standard hydrogen sensor was also prepared by depositing Pt Schottky contacts on the asgrown sample using same processing tools and under identical parameters. Hydrogen detection was carried out at room temperature in an enclosed chamber. Pt/porous GaN sensor exhibited a significant change of current upon exposure to 2% H2 in N2 as compared to the standard Pt/GaN sensor. Morphological studies by scanning electron microscopy (SEM) revealed that Pt contact deposited on porous GaN have a very rough surface morphology with pores distributed all over the contact layer. Therefore, the steep increase of current could be attributed to the unique microstructure at porous Pt/porous GaN interface, which allowed higher accumulation of hydrogen and eventually led to stronger effect of the Hinduced dipole layer.
Porous wide bandgap semiconductors have been widely studied in the last decade due to their unique properties compared to the bulk crystals. The high surface area, shift of bandgap, luminescence intensity enhancement and efficient photoresponse when porosity is formed can be tailored to fabricate new sensing devices. In this work, porous GaN was prepared by ultraviolet (UV) assisted electroless chemical etching method. The commercial Si doped n-type GaN film grown on two inches diameter sapphire (0001) substrate with GaN thickness of 5.5 μm was used in this study. The wafer was then cleaved into few pieces, and these samples were etched in HF:H2O2:CH3OH under UV illumination for 60 minutes. The structural properties was characterized using Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM). Hydrogen sensor was subsequently fabricated by depositing Pt Schottky contact onto the porous GaN sample. The effect of sensing dilute H2 gas with different concentration which is 1% and 2% H2 in a N2 gas ambient was analyzed. The Schottky barrier height of the gas sensor samples was reduced upon exposure to gas. The porous GaN resulted better sensitivity compared to the as grown GaN sample in H2 gas sensing
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