scholarly journals Raman characterization of the optical phonons in AlxGa1−xN layers grown by MBE and MOCVD

1997 ◽  
Vol 2 ◽  
Author(s):  
A. Cros ◽  
H. Angerer ◽  
R. Handschuh ◽  
O. Ambacher ◽  
M. Stutzmann
Keyword(s):  
Phonon Mode ◽  
Aluminum Content ◽  
Composition Range ◽  
Theoretical Calculations ◽  
Phonon Modes ◽  
Sapphire Substrates ◽  
Mode Behavior ◽  
Raman Characterization

We present the results of Raman measurements performed on AlxGa1−xN layers grown by MBE and MOCVD. The films were deposited on (0001) c-sapphire substrates, and the aluminum content covered the whole composition range for x from 0 (GaN) to 1 (AlN). It is shown that the energies of both A1(TO) and A1(LO) phonon modes smoothly increase with increasing x, indicating a one-mode behavior. The E2 phonon mode, however, presents a different behavior. Its energy increases very slowly with aluminum content and, for x≈0.4, a new phonon mode shows up which is shifted to higher energies by 50 cm−1. This new line leads to the E2 AlN mode for increasing aluminum content. The linewidths and intensities of these modes strongly depend on composition. These results are compared with recent theoretical calculations. Finally, the Raman selection rules in the MBE and MOCVD samples are compared and conclusions about the quality of the layers are drawn.

Nondestructive Characterization of GaN Films Grown at Low and High Temperatures

1999 ◽  
Vol 591 ◽  
Author(s):  
C.H. Yana ◽  
H.W. Yao ◽  
J.M. Van Hove ◽  
A.M. Wowchak ◽  
P.P. Chow ◽  
...  
Keyword(s):  
Surface Roughness ◽  
High Temperatures ◽  
Sapphire Substrates ◽  
Wurtzite Crystal Structure ◽  
Phonon Spectra ◽  
Scattering Geometry ◽  
Back Scattering ◽  
Nondestructive Characterization

ABSTRACTGaN films grown on GaAs and sapphire substrates by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) at both low and high temperatures (LT and HT) were characterized by Raman scattering and variable angle spectroscopic ellipsometry (VASE). Optical phonon spectra of GaN films are obtained through back-scattering geometry. Crystal quality of these films was qualitatively examined using phonon line-width. Phonon spectra showed that the HT GaN has wurtzite crystal structure, while LT GaN and GaN/GaAs have cubic-like structures. Thickness nonuniformity and defect-related absorption can be characterized by pseudo dielectric functions directly. Surface roughness also can be determined by using an effective-medium approximation (EMA) over-layer in a VASE analysis. Anisotropic optical constants of GaN, both ordinary and extraordinary, were obtained in the spectral range of 0.75 to 6.5 eV with the consideration of surface roughness, through the small and large angles of incidence, respectively. The film thickness of the GaN was accurately determined via the analysis as well.

Study of Highly Strained Single InAs−In0.53Ga0.47As Quantum Wells from Phonon Modes by Raman Scattering

1995 ◽  
Vol 379 ◽  
Author(s):  
L. G. Quagliano ◽  
D. Orani ◽  
A. Ricci ◽  
M. G. Simeone ◽  
M. R. Bruni
Keyword(s):  
Raman Spectroscopy ◽  
Quantum Wells ◽  
Molecular Beam ◽  
Phonon Mode ◽  
Phonon Modes ◽  
Long Wavelength ◽  
Raman Study ◽  
Highly Strained ◽  
Inp Substrates

ABSTRACTWe report Raman study of highly strained single InAs−In0.53Ga0.47As quantum wells grown by molecular beam epitaxy (MBE) on InP substrates with the well thickness between 4 and 15 monolayers. We have used Raman spectroscopy to characterize quality, disorder and strain of these structures which are of considerable interest for long wavelength optical communications.In the Raman spectra we have observed an intense narrow line corresponding to the GaAslike LO mode of In0.53Ga0.47As cap layer and a narrow peak due to the LO phonon mode of the InAs layer. These dominant and sharp features characterize the high homogeneity of our samples. In addition to these features we have observed the appearance of distinct peaks with the increase of the InAs layer thickness. In our opinion the presence of these modes is indicative of a slight deterioration of the structural perfection of the sample with the increase of the well thickness. Our investigation shows the ability of Raman spectroscopy to describe these systems and the good quality of our structures.

scholarly journals Synthesis of Natural-Like Snow by Ultrasonic Nebulization of Water: Morphology and Raman Characterization

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4458
Author(s):  
Ettore Maggiore ◽  
Matteo Tommasini ◽  
Paolo M. Ossi
Keyword(s):  
Raman Spectroscopy ◽  
Production Method ◽  
Optical Microscope ◽  
Low Density ◽  
Effective Strategy ◽  
Ultrasonic Nebulization ◽  
Raman Characterization ◽  
Snow Samples

The current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water and its subsequent condensation on the cold surfaces of a refrigerator. Inspection of the snow samples with a stereo optical microscope shows both dendritic and granular snow morphologies. The characterization of the samples by Raman spectroscopy shows a behavior consistent with that of a natural, low-density snow. Our results indicate that ultrasonic nebulization of water is an effective strategy for producing natural-like snow at the laboratory scale.

Micro-Raman Characterization of 4H-SiC Stacking Faults

2014 ◽  
Vol 778-780 ◽  
pp. 378-381 ◽  
Author(s):  
Nicolo’ Piluso ◽  
Massimo Camarda ◽  
Ruggero Anzalone ◽  
Francesco La Via
Keyword(s):  
Stacking Faults ◽  
Longitudinal Optical ◽  
Raman Mode ◽  
Plasmon Coupling ◽  
Stacking Sequence ◽  
Strongly Correlated ◽  
Phonon Modes ◽  
Spatial Morphology ◽  
Raman Characterization

Micro-Raman characterization has been used as alternative technique to the photoluminescence in order to detect and study 4H-SiC stacking faults. The alteration of the crystalline stacking sequence perturbs the phonon-plasmon coupling which acts between the crystalline phonon modes and the electronic plasma, due to the doping element (N). The shape and the symmetry of the Longitudinal optical Raman mode is strongly correlated to the doping level of the material thus, through the monitoring of the Raman mode, the spatial morphology of the defect can be completely recovered and compared to the results provided by photoluminescence technique. The results show that such a technique allows a very fast inspection on large wafer, because it is totally independent of the stacking fault photoluminescence signals, which cover a large energy range, up to 0.7 eV.

scholarly journals Microstructural Characterization of High Indium-Composition InXGa1−XN Epilayers Grown on c-Plane Sapphire Substrates

2013 ◽  
Vol 19 (S5) ◽  
pp. 145-148 ◽  
Author(s):  
Myoungho Jeong ◽  
Hyo Sung Lee ◽  
Seok Kyu Han ◽  
Eun-Jung-Shin ◽  
Soon-Ku Hong ◽  
...  
Keyword(s):  
Green Light ◽  
Microstructural Characterization ◽  
Misfit Strain ◽  
Ingan Layer ◽  
Light Emitting ◽  
Composition Modulation ◽  
Sapphire Substrates ◽  
Crystallographic Planes

AbstractThe growth of high-quality indium (In)-rich InXGa1−XN alloys is technologically important for applications to attain highly efficient green light-emitting diodes and solar cells. However, phase separation and composition modulation in In-rich InXGa1−XN alloys are inevitable phenomena that degrade the crystal quality of In-rich InXGa1−XN layers. Composition modulations were observed in the In-rich InXGa1−XN layers with various In compositions. The In composition modulation in the InXGa1−XN alloys formed in samples with In compositions exceeding 47%. The misfit strain between the InGaN layer and the GaN buffer retarded the composition modulation, which resulted in the formation of modulated regions 100 nm above the In0.67Ga0.33N/GaN interface. The composition modulations were formed on the specific crystallographic planes of both the {0001} and {0114} planes of InGaN.

Raman Characterization of Strained GaNyAs1-y and InxGa1-xNyAs1-y Epilayers

2003 ◽  
Vol 798 ◽  
Author(s):  
Li-Lin Tay ◽  
David J. Lockwood ◽  
James A. Gupta ◽  
Zbig R. Wasilewski
Keyword(s):  
Nitrogen Concentration ◽  
Quaternary Alloy ◽  
Epitaxial Films ◽  
Linear Increase ◽  
First Order ◽  
Mode Behavior ◽  
Longitudinal Optic ◽  
Transverse Optic ◽  
Raman Characterization

ABSTRACTPseudomorphically strained epitaxial films of the ternary alloy GaNyAs1-y have been grown on GaAs(100) with y ranging from 0 to 0.05. The optical phonon Raman spectrum of the alloy displays a two-mode behavior. The GaAs-like first order modes are represented at y = 0.05 by the strong longitudinal optic (LO1) mode at 288.5 cm-1 and the weaker transverse optic (TO1) mode at 268.3 cm-1, while the GaN-like LO2 mode is observed at 474.8 cm-1. Two very broad disorder-induced acoustic bands are evident at 80 and 170 cm-1 due to atomic disorder within the crystalline network. Raman studies show that as the nitrogen concentration increases, the GaAs-like LO1 band shifts linearly towards lower wavenumber while the GaN-like LO2 phonon band displays a sub-linear increase in wavenumber. Raman results for the unstrained quaternary alloy In0.06Ga0.94N0.02As0.98 are compared with those of GaN0.02As0.98.

Structural and optical properties of MOCVD InAlN epilayers

2005 ◽  
Vol 892 ◽  
Author(s):  
S. Hernández ◽  
K. Wang ◽  
D. Amabile ◽  
E. Nogales ◽  
D. Pastor ◽  
...  
Keyword(s):  
Optical Properties ◽  
Composition Range ◽  
Theoretical Calculations ◽  
Stokes Shift ◽  
Linear Increase ◽  
Defect Structures ◽  
Frequency Range ◽  
Structural And Optical Properties ◽  
Mode Behavior ◽  
Lattice Matched

AbstractWe have studied the structural and optical properties of InAlN alloys with compositions nearly lattice-matched to GaN. Scanning electron microscopy measurements reveals a good overall surface quality, with some defect structures distributed across the surface whose density increases with the InN concentration. On the other hand, Raman scattering experiments show three peaks in the frequency range between 500 and 900 cm-1, which have been assigned to InN-like and AlN-like E2 modes and A1(LO) mode of the InAlN. These results agree with theoretical calculations previously reported where two-mode and one-mode behavior was predicted for the E and A(LO) modes, respectively. Photoluminescence and photoluminescence excitation allowed us to determine the emission and absorption energies of the InAlN epilayers. Both energies display a redshift as the InN fraction increases. We find a roughly linear increase of the Stokes shift with InN fraction, with Stokes shift values of ≈0.5 eV in the composition range close to the lattice-matched condition.

UV Raman Study of A1(LO) and E2 Phonons in InGaN Alloys Grown by Metal-Organic Chemical Vapor Deposition on (0001) Sapphire Substrates

2000 ◽  
Vol 639 ◽  
Author(s):  
Dimitri Alexson ◽  
Leah Bergman ◽  
Robert J. Nemanich ◽  
Mitra Dutta ◽  
Michael A. Stroscio ◽  
...  
Keyword(s):  
Vapor Deposition ◽  
Phonon Mode ◽  
Chemical Vapor ◽  
Organic Chemical ◽  
Sapphire Substrates ◽  
Mode Behavior ◽  
Uv Raman Spectroscopy ◽  
Metal Organic ◽  
Uv Raman ◽  
Organic Chemical Vapor Deposition

ABSTRACTWe report on UV Raman spectroscopy of InxGa1−xN thin films grown on (0001) sapphire substrates using a specially designed metal-organic chemical vapor deposition (MOCVD) reactor. Eight films were examined in the compositional range 0<×<0.50. Mid and deep-UV Raman spectroscopy was done with the 325.2 nm line of the HeCd laser and the 244 nm line of a double frequency Ar ion laser. The mode behavior of the A1(LO) and E2 phonons was also investigated. We have found compelling evidence for one-mode behavior for the A1(LO) phonon mode, while our data for the E2 mode deviates from the predictions for one-mode behavior. The results for the A1(LO) mode are consistent with the previously reported phonon mode behavior in AlGaN alloys. Also, evidence regarding the presence of compositional inhomogeneities and spinodal decomposition in InGaN thin films is presented.

Physicochemical and bacteriological characterization of hospital effluents and their impact on the environment

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Human Health ◽  
Fecal Coliforms ◽  
Chemical Pollution ◽  
Hospital Effluents ◽  
Biological Contaminants ◽  
Almost All ◽  
Direct Discharge ◽  
Significant Chemical

Liquid effluents discharged by hospitals may contain chemical and biological contaminants whose main source is the different substances used for the treatment of patients. This type of rejection can present a sanitary potentially dangerous risk for human health and can provoke a strong degradation of diverse environmental compartments mainly water and soils. The present study focuses on the quality of the liquid effluents of Hassani Abdelkader’s hospital of Sidi Bel-Abbes (West of Algeria). The results reveal a significant chemical pollution (COD: 879 mgO2/L, BOD5: 850 mgO2/L, NH4+ : 47.9 mg/l, NO2- : 4.2 mg/l, NO3- : 56.8 mg/l with respect to WHO standard of 90 mgO2/L, 30 mgO2/L, 0.5 mg/l, 1 mg/l and 1 mg/l respectively). However, these effluents are biodegradable since the ratio COD/BOD5 do not exceeded the value of 2 in almost all samples. The presence of pathogen germs is put into evidence such as pseudomonas, the clostridium, the staphylococcus, the fecal coliforms and fecal streptococcus. These results show that the direct discharge of these effluents constitutes a major threat to human health and the environment.

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