Papers by Author: Mat Johar Abdullah

Abstract: In this work, structural, optical and electrical properties of nitrogen doped (N-doped) cupric oxide (CuO) thin films deposited on <100> orientated n-type silicon, glass and polyethylene terephthalate substrates using reactive radio frequency sputtering system were investigated. X-ray diffraction results revealed that all films exhibited monoclinic CuO(-111) and have only slightly different structural properties for various substrates. Field effect scanning electron microscopy shown N-doped CuO on Si and glass are denser than on PET substrates and all have nanotriangle-like structure morphologies. The N-doped CuO thin films have an indirect band gap of around 1.30 eV. The resistively, carrier concentration and hall mobility of the N-doped CuO thin film on glass were 1.05 kΩ.cm, 6.70 x 10¹⁴ cm^-3 and 8.86 cm²/V-s respectively. Furthermore, palladium formed ohmic contact characteristics for N-doped CuO on glass and PET but exhibited schottky contact characteristics for N-doped CuO on Si.

Abstract: In this work, cuprous oxide (Cu₂O) thin films grown on glass and polyethylene terephthalate (PET) substrates using reactive radio frequency magnetron sputtering system were investigated. Copper target with purity of 99.99% were used while high purity argon-oxygen gases were utilized as sputtering gases. Structural, morphological, and optical properties of the films were investigated by X-ray diffraction (XRD), atomic force microscopy and ultra-violet visible spectrophotometer. From the XRD results, only one single diffraction peak corresponding to cubic Cu₂O (111) crystal structure were observed for both substrates. The surface morphologies of the samples were in a form of pillar-like. Root mean square surface roughness for Cu₂O on glass and PET substrates were 3.37 nm and 3.20 nm, respectively. The films were highly transparent for wavelength above 600 nm. The Cu₂O films have direct band gap values of around 2.56 eV as determined by Taucs method.

Abstract: This paper reports the temperature dependent DC and RF characteristics of n-GaN Schottky diode simulated using Atlas/Blaze developed by Silvaco. It was found that as the temperature increases from 300K to 900K the forward current decreases due to lowering of the Schottky barrier with an increase in series-resistance and ideality factor. These observations indicates that tunneling behavior dominates the current flow rather than thermionic emission. Furthermore, the breakdown voltage decreases in reverse bias and insertion loss for RF behavior increases with respect to temperature due to the increase in capacitance near diode junction.Keywords: Atlas/Blaze, Schottky barrier, series resistance, ideality factor, insertion loss.

Abstract: Cobalt-doped ZnO nanorods were successfully synthesized on SiO₂/Si substrate using RF-magnetron sputtering at room temperature. The structural, morphological, and photoluminescence (PL) properties of undoped and Co-doped ZnO nanostructure were characterized using X-ray diffraction, field emission-scanning electron microscopy, and PL analyses. The results showed that Co²⁺ replaces Zn²⁺ in the ZnO lattice without changing the wurtzite structure. As the Co concentration increases, the structure becomes highly crystalline and is gradually converted into nanorods with no extra phases. The as-synthesized nanorod arrays are dense and vertically grow on the SiO₂ substrate. The arrays exhibit diameters of approximately 56.89 nm as well as lengths that range from 247.9 nm to 527.5 nm. PL analysis reveals that the ultraviolet (UV) emission intensity decreases and exhibits a blue shift as the Co doping level is increase.

Abstract: In this work, a chemically grown ZnO rod – like structure is produced via precipitation and post – sonication treatment based on the hydrolysis of zinc iodide (ZnI₂) and diethanolamine (DEA). ZnO rod – like structures with aspect ratio of 3 to 4(diameter of 235 nm and 800 nm in length) was observed from the TEM micrograph.The as-synthesized ZnO wurtzite structure was compared to sample without ultrasonic irradiation treatment to study the effect of bubble implosion on the formation of the particle. In contrast to particles treated with ultrasonic irradiation, micron sized and agglomerated particles were observed in sample without the treatment. The mechanism related to acoustic cavitations and the formation of rod – like structure is explained. The XRD results show polycrystalline structure on both samples. The optical property of ZnO was evaluated using room temperature UV - Visible absorption spectroscopy. The result showed an absorption peak at 381 nm in wavelength.

Abstract: AlN doped ZnO thin films were prepared on glass and Si (100) substrates by RF sputtering. For AlN doped ZnO at RF powers of 200 W (ZnO target) and 200W (AlN target), the ZnO (002) peak showed the highest intensity at the substrate temperature of 400˚ C. The prepared films showed good transmission of above 72 % in the visible range. The calculated values of energy band gaps were in the range (3.42 eV - 3.54 eV) for the films prepared at different substrate temperatures.

Abstract: We report the deposition of aluminium doped zinc nitride film (Al-Zn₃N₂) on glass substrates by RF sputtering. Thermal oxidation of the film under different annealing temperature (500°C to 600°C) was carried out. Structural and electrical properties of the annealed films were investigated. XRD analysis showed that Al-Zn₃N₂ film was successfully converted into Al-N zinc oxide (ANZO) at 500°C. I-V characteristics of the films were measured and the lowest estimated resistivity of the films of 4kΩ.cm can be achieved at 600°C.

Abstract: In this paper, we studied growth of AlN/GaN/AlN on Si (111) by using plasma assisted molecular beam epitaxy (PA-MBE) system. The structural and optical characteristics of the sample have been investigated by using high resolution X-ray diffraction (HR-XRD), Raman spectroscopy and photoluminescence (PL). PL spectrum of the sample has shown sharp and intense band edge emission of GaN with the absence of yellow emission band, indicating good crystal quality of the sample. The silver (Ag) metal contact was then deposited on the sample followed by thermal treatment at 500°C and 700°C, respectively. Treated sample at 700°C showed good spherical Ag islands on sample compared to the treated sample at 500°C. The effect of Ag islands on the electrical characteristics of sample was also examined by using I-V measurement. The results showed that the treated sample at 700°C has decreased the photo-current of Schottky diode.

Abstract: High quality undoped Al_xGa_1-xN with high Ga composition was grown on Si (111) substrate, using GaN/AlN as the buffer layer, by plasma-assisted molecular beam epitaxy (PAMBE). The present work reports on the photoluminescence (PL) studies of porous Al_xGa_1-xN prepared by ultraviolet (UV) assisted electrochemical etching in a solution of 2 % concentration of KOH electrolyte under illumination of an UV lamp with 500 W power for 30 min. The optical properties of porous Al_xGa_1-xN sample was compared to the corresponding as-grown GaN. PL studies suggested that the porosity was capable of improving the lattice mismatch induced strain. Porosity induced PL intensity enhancement was found in nanoporous sample. The resulting nanoporous Al_xGa_1-xN display red-shifted PL spectra compared to the as-grown Al_xGa_1-xN. Appearance of the red-shifted emission is correlated with the development of highly anisotropic structures in the morphology.

Abstract: We focus in this paper the temperature variation effects on the current – voltage ( I-V) characteristics of n-GaN schottky diode. The diode was doped with carrier concentration 1*1013cm-3 and Pt electrode was used. The simulated current were obtained at temperatures from 50K to 500K and voltage up to 2Volt. We use the Srh (Schokley read hall), Cvt (Lombardi Model), Auger (Auger), Fermi (Fermi Dirac), Impact, Bgn (Bandgap Narrowing), Complete ioniz model to get the schottky rectifying current – voltage (I-V) characteristics.. We find that by increasing the temperature from 50K to 500K, the forward schottky rectifying current decreases from 2.7187 Amp to 0.383 Amp. while the forward turn – on voltage decreases. In reverse bias at low temperature the current is high and we increase the temperature the current decreases. The breakdown voltage decreases at higher temperature.