P.K. Ooi

Surface and interface phonon polariton characteristics of wurtzite ZnO/GaN heterostructure

Surface and interface phonon polariton modes in wurtzite ZnO/GaN heterostructure on wurtzite 6H–SiC substrate were investigated by a variable angle p-polarized infrared attenuated total reflection spectroscopy. Three dips corresponding to the surface and interface phonon polariton modes were observed; two of the dips that having a lower intensity level of reflectivity were the leaky modes whereas, another one was a real mode. The observations were verified with the surface polariton dispersion curve simulated based on an anisotropy model for a four-layer system. It was shown that the frequencies of leaky modes are predictable by considering the damping of the substrate.Surface and interface phonon polariton modes in wurtzite ZnO/GaN heterostructure on wurtzite 6H–SiC substrate were investigated by a variable angle p-polarized infrared attenuated total reflection spectroscopy. Three dips corresponding to the surface and interface phonon polariton modes were observed; two of the dips that having a lower intensity level of reflectivity were the leaky modes whereas, another one was a real mode. The observations were verified with the surface polariton dispersion curve simulated based on an anisotropy model for a four-layer system. It was shown that the frequencies of leaky modes are predictable by considering the damping of the substrate.

Structural and morphological properties of zinc oxide thin films grown on silicon substrates

In this work, the effects of surface orientation of the silicon (Si) substrates on the structural and morphological properties of zinc oxide (ZnO) thin films grown by radio frequency sputtering system were investigated. Silicon substrates with different surface orientations, i.e., Si(100), Si(111), and Si(110) were used. The structural properties of the ZnO thin films were investigated by X-ray diffraction (XRD) technique. The morphological properties of the deposited films were examined by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD results reveal that all the deposited ZnO thin films exhibit a single phase wurtzite ZnO structure with preferred orientation along (002) direction. The FESEM images indicate a change from leave-like to granular-like structure for Si(100), (110) and (111) substrates, respectively. The AFM root mean square surface roughness for ZnO thin films on Si(100), (110) and (111) reveals a decreasing trend. From the results, it was sugg...

Polarized infrared reflectance characterization of wurtzite ZnO/GaN heterostructure on 6H-SiC substrate

Infrared (IR) optical properties of a wurtzite ZnO/GaN heterostructure on a wurtzite 6H-SiC substrate are characterized by a polarized IR reflectance spectroscopy. The relation between the reststrahlen features and the optical phonon modes of each individual layer are investigated. It is shown that the transverse magnetic polarized IR reflectance spectrum provides the least loss of information about the optical phonon frequencies of wurtzite crystal. By means of the standard multilayer optics technique and based on an anisotropic dielectric function model, polarized IR reflectance spectra of the studied structure are simulated. Numerical fitting procedure is applied to obtain the best fit of experimental and theoretical spectra. Finally, the optical phonon frequencies and the layers thicknesses of the studied structures are determined.

Effects of sputtering power on properties of copper oxides thin films deposited on glass substrates

Copper oxides are deposited by radio frequency sputtering using copper target in the mixture of argon and oxygen gasses. The structural and optical properties of the copper oxides deposited at different sputtering powers have been investigated. All the films are single phase polycrystalline. At low RF power (100 W), the film is monoclinic structure of cupric oxide (CuO). Meanwhile, the films are cubic structure of cuprous oxide (Cu2O) at higher RF power. Field emission scanning electron microscopy images show the films have different morphologies with small grain size and consist of a lot of voids. The analysis of energy dispersive X-ray spectroscopy shows that the ratio of Cu to O is increased as the RF power increased. From the ultraviolet–visible spectroscopy, the films have a broad absorption edge in the range of 300–500 nm. The band gap of the films grown at RF power of 100 W, and 120 W and above, were 1.18 eV and 2.16 eV, respectively.

Characterizations of Nitrogen Doped Cupric Oxide Thin Films Deposited on Different Substrates for Solar Cell Applications

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.

Characteristics of Cuprous Oxide Thin Films Deposited on Glass and Polyethylene Terephthalate Substrates

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.