S. S. Ng

Surface phonon polariton mode of wurtzite structure AlxGa1−xN(0⩽x⩽1) thin films

Surface phonon polariton (SPP) mode of wurtzite structure AlxGa1−xN (0⩽x⩽1) thin films is investigated experimentally and theoretically. The influences of the alloy composition x on the position and the line width of SPP mode are reported. The results showed that the SPP absorption peak exhibits one-mode behavior and is subjected to broadening as x is increased. Reasonable agreement between the experimental and the theoretical results is also obtained. Finally, the composition dependence of the SPP mode with bowing parameter of −72.5cm−1 is determined.

Polarized infrared reflectance study of wurtzite GaN thin film: The effects of angle of incidence on the optical phonon modes

We report on the polarized IR reflectance study of wurtzite GaN thin film grown on 6H‐SiC substrate measured at various angles of incidence, namely, from 15° to 75°. Attention is focused on the effects of incident angles on the Brillouin zone center optical phonon modes of the GaN thin film. The reflection spectra are compared to the calculated spectra generated with a damped single harmonic oscillator model. Good agreement between the measured and calculated spectra has been obtained. Overall, the results revealed that the optical phonon modes of the GaN thin film and 6H‐SiC substrate are independent of the angle of the incidence beam.

Surface phonon polariton characteristics of In 0.04 Al 0.06 Ga 0.90 N/AlN/Al 2 O 3 heterostructure

Surface phonon polariton (SPP) characteristics of In(0.04)Al(0.06)Ga(0.90)N/AlN/Al(2)O(3) heterostructure are investigated by means of p-polarized infrared (IR) attenuated total reflection spectroscopy. Two absorption dips corresponding to In(0.04)Al(0.06)Ga(0.90)N SPP modes are observed. In addition, two prominent dips and one relatively weak and broad dip corresponding to the Al(2)O(3) SPP mode, In(0.04)Al(0.06)Ga(0.90)N/Al(2)O(3) interface mode, and Al(2)O(3) bulk polariton mode, respectively, are clearly seen. No surface mode feature originating from the AlN layer is observed because it is too thin. Overall, the observations are in good agreement with the theoretical predictions.

Composition Dependence of Surface Phonon Polariton Mode in Wurtzite InxGa1?xN (0 ? x ? 1) Ternary Alloy

We present a theoretical study on the composition dependence of the surface phonon polariton (SPP) mode in wurtzite structure ?-InxGa1-xN ternary alloy over the whole composition range. The SPP modes are obtained by the theoretical simulations by means of an anisotropy model. The results reveal that the SPP mode of ?-InxGa1-xN semiconductors exhibits one-mode behaviour. From these data, composition dependence of the SPP mode with bowing parameter of ?28.9 cm?1 is theoretically obtained.

Determination of the Al Composition of Al{sub x}Ga{sub 1-x}N Thin Films By Means Of EDX and XRD Techniques

In this paper, the determinations of Al composition x of AlxGa1−xN (0⩽x⩽1) thin films by means of the energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD) analyses are reported. Through these non‐destructive and contactless techniques, a large probed area of the AlxGa1−xN samples can be selected. Consequently, the uncertainty due to the inhomogeneity of the Al composition can be avoided. For EDX measurements, the Al composition is calculated based on the weight percent of the Al and Ga elements, while that in the XRD measurements is based on lattice constant c and Vegard’s law. The results from these two independent techniques are in good agreement with each other.

Kramers-Kronig Analysis of Infrared Reflectance Spectra for Quaternary In{sub x}Al{sub y}Ga{sub 1-x-y}N Alloy

In this paper, a Kramers‐Kronig (KK) analysis of infrared (IR) reflectance spectrum of quaternary In0.01Al0.06Ga0.93N film grown by molecular beam epitaxy (MBE) is reported. The infrared measurement is performed in the reflection mode at an incident angle of 15° by Fourier transform infrared (FTIR) spectroscopy at Tu2009=u2009300u2009K. The Kramers‐Kronig analysis of the reflectivity data has been used to obtain the real and imaginary parts of the index of refraction (n and k), and the real and imaginary parts of the dielectric response function (e’ and e’) of the materials. Finally, the transverse optical and longitudinal optical phonons for quaternary InxAlyGa1−x−yN were obtained.

Structural and optical properties of Alx Iny Ga1−x−y N quaternary alloys grown on sapphire substrates by molecular beam epitaxy

Purpose – The purpose of this paper is to study the structural and optical characterization of Alxu2009Inyu2009Ga1−x−yu2009N quaternary epilayers, which were grown on c‐plane (0001) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy technique with indium (In) mole fraction y ranging from 0.0 to 0.1 and constant aluminum (Al) mole fraction x=0.06.Design/methodology/approach – High‐resolution X‐ray diffraction rocking curve (HRXRD‐RC), scanning electron microscopy (SEM), energy dispersive X‐ray spectrometry (EDX), and photoluminescence (PL) spectroscopy have been measured on quaternary Alxu2009Inyu2009Ga1−x−yu2009N thin films at room temperature.Findings – HRXRD‐RC measurements confirmed that the Alxu2009Inyu2009Ga1−x−yu2009N alloys had wurtzite structure. SEM images, element composition analysis by EDX, provided the evidence to show the existence of defects inside the samples contaminated by silicon from previous growth leading to nonuniformity of the epilayers, which caused decreased in the quality of...

The Study of Energy Band Gap of InxAlyGa1−x−yN Quaternary Alloys using UV‐VIS Spectroscopy

Quaternary InxAlyGa1−x−yN alloys with indium (In) mole fraction x ranging from 0.01 to 0.10 and constant aluminum (Al) mole fraction yu2009=u20090.06, were grown by molecular beam epitaxy. The energy band gaps of InAlGaN alloys were investigated using UV‐VIS spectroscopy under room temperature. The energy band gap decreases with increasing In composition from 0.01 to 0.08. This trend is expected since the incorporation of In lowers the energy band gap of Al0.06Ga0.94N (3.72 eV). However, for InAlGaN with In composition of 0.1, the band gap shows a sudden increase in energy. This is probably due to local alloy compositional fluctuations in the epilayer, contributed by incomplete substitutions of Ga atoms by the In atoms, thus retaining a much richer GaN structure. Finally, we investigate the bowing parameter appears also to be very sensitive on In content. We obtained bu2009=u200950.08 for quaternary InAlGaN alloys.

Influence of initial sulfur content in precursor solution for the growth of molybdenum disulfide

This work investigated the influence of initial sulfur content in the precursor solution for the growth of molybdenum disulfide (MoS2) films by thermal vapour sulfurization (TVS) with sol-gel spin coating as pre-deposition technique. The early introduction of sulfur shows the presence of grains are uniformly distributed and homogeneous on the surface of the film. MoS2 (002) planes are detected for both films with and without initial sulfur conditions, however, the presence of initial sulfur contents gives slightly higher intensity of diffraction peak. Two phonon modes for MoS2, namely the E2g 1 (in-plane) and the A1g (out-of plane), are well detected from which the frequency difference of Raman peaks between E2g 1 and A1g suggest the grown MoS2 consisted of multi-layers. There is a slight shift of E2g 1 which is caused by the carbon impurities but no shift for A1g. Besides, MoS2 film with the presence of initial sulfur content shows better crystal as indicated by its narrower Raman peaks linewidth. Two broad absorption peaks of MoS2 are detected at 614nm and 665nm. Hence, the early introduction of sulfur content in prepared precursor solution is one way of optimizing the growth of MoS2 films.

Polarized infrared attenuated total reflection study of sapphire crystals with different crystallographic planes

Polarized infrared (IR) attenuated total reflection (ATR) measurements were performed on c- (polar) and r-plane (semi-polar) sapphire crystals. For c-plane sapphire crystal, spectral features due to the surface phonon polariton (SPhP) modes are only observable in the p-polarized ATR spectrum. Calculation of the SPhP dispersion spectra revealed that the SPhP modes of r-plane sapphire crystal are possible to be observed in both the s- and p-polarized ATR spectra. ATR measurements verified that excitation of the SPhP modes are still easier in the p-polarized ATR spectra. Taking into account the effects of anisotropy and the crystal orientation of hexagonal crystal system, the ATR spectra of r-plane sapphire crystal with arbitrary orientations were simulated. Through a best fit of experimental with simulated spectra, information about the crystal orientation of sapphire crystals was deduced.