Papers by Keyword: Porous GaN

Abstract: The fabrication of porous GaN (PGaN) by UV-assisted electrochemical etching with a variations of current densities (40, 60, and 80 mA/cm²) for 60 min in electrolytes consisting of 4% KOH are reported. Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to characterize the morphological and structural characteristics of the PGaN. All PGaN sample prepared by electrochemical etching technique produced a hexagonal-like pore shape. FESEM images demonstrated that the pore uniformity and porosity are affected significantly by the current density. The PGaN sample fabricated with 80 mA/cm² produces a uniform and high porosity structure compared to other PGaN sample. This shows that the morphology and structural characteristic of PGaN are increase with the increase of current density. The EDX result revealed significant Ga and N atom presence in all samples. However, the O atom only presence in sample etched with 80 mA/cm² implying that the etching process is occur vigorously in this sample. The AFM verified that the surface roughness and the pore depth are increased as current density increased. There were relatively large variations of the peak intensities for 2Theta-scan patterns as exposed by XRD. The peak shift for PGaN sample relative to as-grown was inconsistent and the changed was relatively small. Raman intensity found to be enhanced with the increase in current density and among the PGaN sample, the E₂(high) peak for sample prepared with 60mA/cm² and 80mA/cm² was observed to be slightly shifted to lower frequency. The PL spectra displayed that the porosity has high impact on the PL peak intensity. . Overall, this proved that with the usage of low power UV light, the pore structure still can be produced as good as pore structure fabricated with high power UV light.

Abstract: 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.

Abstract: 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.

Abstract: Owing to its great potential in optoelectronic devices, structural and surface properties of porous GaN prepared by UV electrochemical etching has been investigated. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and high resolution X-ray diffraction (HR-XRD) phi-scan and rocking curves measurements revealed the nature of the pore morphology and nanostructures. SEM micrograph indicated that the shapes of pores for porous sample are nearly hexagonal. The AFM measurements revealed that the surface roughness increased in the porous sample. X-ray diffraction phi-scan showed that porous GaN sample maintained the epitaxial feature.

Abstract: The structural and optical properties of porous GaN films on sapphire (0001) prepared by UV assisted electrochemical etching were reported in this study. SEM micrographs indicated that the shapes of the pores for both porous samples are nearly hexagonal. As compared to the as-grown GaN films, porous layers exhibit a substantial photoluminescence (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.

Abstract: This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as grown GaN. The samples were investigated by scanning electron microscopy (SEM), high resolution x-ray diffraction (HRXRD), and photoluminescence (PL). The porous area is very uniform, with pore diameter in the range of 80-110 nm. XRD measurements showed that the (0002) diffraction plane peak width of porous samples was slightly broader than the as-grown sample. PL measurements revealed that the near band edge peak of the porous samples were redshifted. Metal-semiconductor-metal (MSM) photodiode was fabricated on the samples. For as grown GaN sample, this detector shows a sharp cut-off wavelength at 362 nm. A maximum responsivity of 0.258 A/W was achieved at 360 nm. For the porous GaN sample, this detector shows a sharp cut-off wavelength at 364 nm. A maximum responsivity of 0.771 A/W was achieved at 363 nm.