S.S. Ng

Experimental and theoretical studies of surface phonon polariton of AlN thin film

The surface phonon polariton (SPP) mode of aluminum nitride (AlN) thin film grown on sapphire substrate is investigated experimentally and theoretically. For the experimental study, p-polarized infrared attenuated total reflection measurements are performed. A strong absorption dip which corresponds to the SPP mode of AlN thin film is clearly observed at 839.0cm−1. For the theoretical study, the surface-polariton dispersion curve of the AlN thin film has been simulated. Finally, the experimental and theoretical values of the SPP mode are compared. The results revealed that the uncertainty between the theoretical and experimental SPP values is less than 2%.

Characterizations of InN thin films grown on Si (110) substrate by reactive sputtering

Indium nitride (InN) thin films were deposited onto Si (110) by reactive sputtering and pure In target at ambient temperature. The effects of the Ar-N2 sputtering gas mixture on the structural properties of the films were investigated by using scanning electron microscope, energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction techniques. The optical properties of InN layers were examined by micro-Raman and Fourier transform infrared (FTIR) reflectance spectroscopy at room temperature. Structural analysis specified nanocrystalline structure with crystal size of 15.87 nm, 16.65 nm, and 41.64 nm for InN films grown at N2/Ar ratio of 100/0, 75/25, and 50/50, respectively. The Raman spectra indicates well defined peaks at 578, 583, and 583 cm-1, which correspond to the A1(LO) phonon of the hexagonal InN films grown at gas ratios of 100 : 0, 75 : 25 and 50 : 50 N2: Ar, respectively. Results of FTIR spectroscopy show the clearly visible TO [E1(TO)] phonon mode of the InN at 479 cm-1 just for film that were deposited at 50 : 50 N2: Ar. The X-ray diffraction results indicate that the layers consist of InN nanocrystals. The highest intensity of InN (101) peak and the best nanocrystalline InN films can be seen under the deposition condition with N2/Ar gas mixture of 50 : 50.

Effect of hydrostatic pressure on the barrier height of Ni Schottky contacts on n-AlGaN

We report measurements of the Schottky barrier height of Ni contacts on Ga-polarity n-Al0.08Ga0.92N as a function of pressure. With applied hydrostatic pressure, Al0.08Ga0.92N Schottky diodes show a decrease in the forward bias current, and correspondingly an increase in the barrier height, which is approximately twice as large as that previously reported for Schottky contacts on Ga-polarity n-GaN. The observed change in barrier height with pressure is attributed to a combination of band structure and piezoelectric effects. The larger change of barrier height for Al0.08Ga0.92N can be explained by its larger piezoelectric constants and smaller density of interface states at the metal-semiconductor interface compared to GaN.

Fabrication of InN based photodetector using porous silicon buffer layer

Abstract We fabricated indium nitride (InN) on porous silicon (PSi) on crystalline silicon [Si(100)] heterostructure photodetector via radio frequency sputtering. PSi layer was synthesised on n type Si(100) wafers via photoelectrochemical etching. Large area PSi, which comprised an array of voids, was used as an intermediate layer between Si and InN thin film. X-ray diffraction results revealed that nanocrystalline wurtzite structure of InN thin film with preferred orientations of InN (101) was deposited on PSi/Si(100) substrate. Nickel Schottky contact was fabricated on InN thin films via thermal vacuum evaporation using a metal semiconductor metal mask. To relieve stress and to induce any favourable reactions between the metals and the semiconductors, the InN photodetector was annealed in an N2 environment. Current–voltage measurements after heat treatment at 400°C were performed in the dark and illuminated conditions.

Surface and interface phonon polaritons of wurtzite GaN thin film grown on 6H-SiC substrate

Surface and interface phonon polaritons of wurtzite GaN thin film grown on 6H-SiC substrate are investigated experimentally and theoretically. Two strong absorption peaks that correspond to the surface and interface phonon polaritons are clearly observed at 710 and 916 cm−1, respectively. This observation is in good agreement with the results simulated using an anisotropy model. Finally, the obtained surface phonon polariton (SPP) mode is compared with the reported result. It is revealed that the SPP mode in the wurtzite GaN thin film is shifted toward higher frequency as compared to that in the wurtzite bulk GaN.

Surface phonon polariton characteristic of honeycomb nanoporous GaN thin films

Nanoporous GaN thin films with honeycomb structure were fabricated via ultra-violet assisted electrochemical etching approach. Under different anodization voltages, two nanoporous samples with different porosity were fabricated. Porosity and surface phonon polariton (SPP) characteristics of the fabricated samples were investigated using polarized infrared attenuated total reflection technique. It was found that the porosity of nanoporous GaN has great influence on its SPP resonant frequency. It can modulate the resonance frequency towards lower value.

Comparative study on structural and optical properties of nitrogen rich InN on Si(110) and 6H-SiC

Abstract Nitrogen rich indium nitride (InN) thin films were deposited on anisotropic silicon [Si(110)] and 6H-silicon carbide (6H-SiC) substrates by reactive radio frequency sputtering technique. The surface quality of the InN films on Si(110) substrate was compared to that deposited on 6H-SiC substrate. Both deposited films showed wurtzite nanocrystalline InN films with a (101) preferred growth orientation. One Raman active optical phonon of E2(high) and two Raman and infrared active modes of A1(LO) and E1(TO) of the wurtzite InN thin film were clearly observed for both samples. Morphological characteristics showed higher surface quality for InN grown on Si(110) compared to that on SiC substrate. Owing to the large lattice mismatch, it was found that the crystallinity of InN films grown on 6H-SiC substrate degraded as compared to that grown on Si(110).

Solvothermal growth of single-crystal CdS nanowires

Cadmium sulfide (CdS) nanowires (NWs) were prepared by the solvothermal method using ethylenediamine as a solvent. Two sets of CdS NWs were synthesized at 160 and 200 °C for various reaction durations (3⋅5, 7, and 24 h). Scanning/tunneling electron microscopy was used to examine the surface morphology of the grown NWs. Their dimensions are found to depend on the reaction temperature and duration. The CdS NWs grown at 200 °C for all durations are longer than those prepared at 160 °C, with diameters ranging from 15 to 40 nm. A three-armed structure is exhibited by all the samples. The grown CdS NWs display a hexagonal wurtzite phase and grows along the 001

High-Quality ZnCdS Nanosheets Prepared Using Solvothermal Synthesis

\mathbf {\left \langle {001}\right \rangle }

Far Infrared Optical Properties of Bulk Wurtzite Zinc Oxide Semiconductor

direction. The optical absorption of the grown NWs shows a sharp absorption edge with a blueshift, which indicates an expansion of the optical band gap. All prepared samples show two emission peaks in their photoluminescence spectra. The emission peak location depends on the reaction temperature and duration. The CdS NWs prepared at 160 °C show a sharp band–band emission compared with those prepared at 200 °C. Raman analysis indicates that the optical properties of the grown NWs are enhanced with increased temperature and reaction duration.