Papers by Author: Sha Shiong Ng

Abstract: The study signifies the radio-frequency (RF) sputtering growth and characterizations of indium nitride (InN) thin films deposited on flexible substrates. A three-inch diameter indium (In) sputtering target with purity of 99.999% was used. The deposition was carried out at room temperature and with substrate temperature of 200 °C. The surface morphologies, structural and optical properties of the deposited thin films were examined by using field-emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction as well as Fourier transform infrared spectroscopy. All the results revealed that InN thin films have been successfully deposited on the flexible substrates in the gas mixture ambient of argon and nitrogen.

Abstract: In this work, room temperature polarized infrared attenuated total reflection (ATR) spectroscopy was employed to characterize a nanoporous GaN thin film with honeycomb structure. Prominent ATR dips due to the surface phonon polariton (SPP) and guided waves of nanoporous GaN thin film were observed. Both SPP resonance and guided waves were detected in the p-polarized ATR spectrum while only guided waves were detected in the s-polarized ATR spectrum. The ATR results were compared with the theoretical spectra generated by means of effective medium model. Good agreement was achieved between the measured and theoretical spectra. Finally, the thickness and porosity of porous layer were determined unambiguously.

Abstract: Heterostructures consisting of ZnO and diamond appear to have an elusive nature. A rectifying behaviour was previously observed only for heterojunctions with very lightly doped p-type diamond using residual boron gas during the chemical vapour deposition process or type IIb diamond. Other studies, however, claimed to obtain a rectifying behaviour for heterojunctions with p-type diamond with higher carrier densities between 10¹⁸ 10¹⁹ cm^-3. In this work we investigate the behaviour of n-type ZnO on heavily boron-doped p-type diamond. This heterostructure that is sensitive to UV light has been fabricated using ZnO nanorods grown on heavily boron-doped chemical vapour deposition diamond substrates. The I - V measurements show a rectifying characteristic. The threshold voltages under dark and UV conditions are 3.66 and 2.52 V, respectively. The UV illumination also results in an increased current flow. The electrical behaviour due to the UV illumination will be discussed.

Abstract: Epitaxial growth of GaN has become an interest topic in term of light emitting device fabrication. Most of the commercial GaN based device is normally grown on sapphire substrate. For power device application, SiC has been found to be a desirable candidate for GaN epilayer due to their high thermal conductivity, small lattice mismatch, and hexagonal lattice mismatch with cleaved facet for the laser cavity. In this paper, X-ray diffraction (XRD) technique is employed to study the structural properties of GaN thin film grown on 6H-SiC substrate. For conventional XRD -2 scan, only diffraction peaks from GaN (002) and its multiple diffractions were observed, along with diffractions from SiC (006) peak. These results suggested that the GaN film is in wurtzite phase. For XRD rocking curve of omega scan of (002) diffraction plane of the GaN, a full width at half maximum of about 259 arcsec is obtained.

Abstract: In this paper, we report on the characterization of a set of MOCVD grown GaN samples with a variety of structural or crystalline quality. X-ray diffraction (XRD) was used to observe the change of the crystalline structure with deposition temperature. All results show that the structure type of the GaN deposited films is sensitive to the growth temperature. Our results also revealed that a good crystalline structure of GaN films could be grown at temperatures higher than 600°C. Finally, a general picture on the correlations between the growth temperature and the GaN deposited films crystalline is reported.

Abstract: Gallium nitride (GaN) is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Thin films of GaN are most commonly grown in the hexagonal wurtzite structure on sapphire substrates. Growth of GaN onto silicon substrates offers a very attractive opportunity to incorporate GaN devices onto silicon based integrated circuits. Although direct epitaxial growth of GaN films on Si substrates is a difficult task (mainly due to the 17% lattice mismatch present), substantial progress in the crystal quality can be achieved using a buffer layer. A full characterization of the quality of the material needs to be assessed by a combination of different techniques. In this work, a detailed characterization study of GaN thin film grown on Si(111) with AlN buffer layer by low pressure metalorganic chemical vapor deposition (LP-MOCVD) was carried out. Post deposition analysis includes scanning electron microscopy (SEM), x-ray diffraction (XRD), Hall and infrared (IR) spectroscopy techniques. The IR spectra were compared to the calculated spectra generated with a damped single harmonic oscillator model. Through this method, a complete set of reststrahlen parameters (such as ε∞, S, wTO, γ) of the GaN epilayer were obtained. Our results show that the GaN film has a single crystalline structure. Current-voltage characteristics (I-V) of this GaN/Si heterojunction were measured at room temperature. Rectification behavior was observed for this anisotype heterojunction. The electrical characteristics of Ni Schottky barriers on this unintentionally doped n-type film were also investigated. The barrier height of Ni/GaN Schottky barriers has been determined to be 0.93 eV by I-V measurement.

Abstract: In this paper, we report the characteristics of GaN heteroepitaxial films grown on Si(111)at 700oC using plasma-assisted metalorganic chemical vapour deposition (PA-MOCVD). In this growth technique, H2 plasma was used in addition to N2 plasma. Two sets of samples with different buffer layers were used, i.e. GaN and AlN buffer layers. In the infrared region both samples exhibit similar reststrahlen band shape. However the sample with GaN buffer layer exhibits better optical properties in the visible region compared with its counterpart. This is attributed to its better structural bulk and surface properties.