Raman Analysis Of AlxGa1-xN Films

1997 ◽  
Vol 482 ◽  
Author(s):  
Leah Bergman ◽  
Mitra Dutta ◽  
Michael D. Bremser ◽  
Ok-Hyun Nam ◽  
William G. Perry ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Alloy System ◽  
High Energy ◽  
Line Broadening ◽  
Model Calculations ◽  
Raman Analysis ◽  
Thermal Expansion Coefficients ◽  
X Ray Scattering ◽  
The Difference ◽  
Superlattice Line

AbstractRaman analysis of the E2 mode of AlxGal-xN in the composition range 0 ≤ x ≤ 1 is presented. The lineshape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the lineshape. The model calculations also indicate the lack of a long-range order in the CVD (chemical vapor deposition) alloys. These results were confirmed by X-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x∼0.5 indicative of a random disordered alloy system. The stress state of the alloys was found to be tensile and was attributed to the difference in the thermal expansion coefficients of the SiC substrate and the film.

A Model for Double Positioning Twin Formation in Cubic SiC on Noncubic SiC Substrates

1992 ◽  
Vol 280 ◽  
Author(s):  
Woo Sik Yoo ◽  
Charles P. Beetz. ◽  
Fen-Ren Chien ◽  
Steven R. Nutt ◽  
Tsunenobu Kimoto ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Coulomb Force ◽  
High Energy ◽  
Electrostatic Model ◽  
Chemical Vapor Deposition Growth ◽  
Growth Simulation ◽  
Transmission Electron ◽  
Energetic Balance ◽  
Twin Formation ◽  
The Difference

ABSTRACTAs an attempt to explain polytype formation and crystal growth of SiC we propose an electrostatic model in which electrostatic Coulomb force is considered as an interatomic force. The dependence of surface potential on the stacking sequence of atoms in substrates was investigated, and the growth simulation was tried considering the energetic balance under various interaction lengths.The model predicts the double positioning twin formation and the difference in area between twins in cubic 3C-SiC growth on hexagonal 6H-SiC and rhombohedral 15R-SiC substrates. The prediction was experimentally tested by simultaneous chemical vapor deposition growth on basal planes of 6H-SiC(0001) and 15R-SiC(0001). Polytype and interface structure of both specimens were investigated by reflection high energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HRTEM).

Interdiffusion Mechanisms in GaAs/AlGaAs Quantum Well Heterostructures Induced by SiO2 Capping and Annealing

1997 ◽  
Vol 484 ◽  
Author(s):  
A. Pépin ◽  
C. Vieu ◽  
M. Schneider ◽  
H. Launois ◽  
E. V. K. Rao
Keyword(s):  
Quantum Well ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Semiconductor Surface ◽  
Simultaneous Generation ◽  
Spatial Control ◽  
Thermal Chemical Vapor Deposition ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
The Difference

AbstractWe have investigated intermixing enhancement in GaAs/AlGaAs quantum well heterostructures achieved by SiO2 capping obtained by rapid thermal chemical vapor deposition. Evidence of fast Ga pumping inside the SiO2 layer during anneal and simultaneous generation of excess Ga vacancies under the SiO2/GaAs interface is presented. A simple model involving the thermal stress arising from the difference in thermal expansion coefficients between SiO2 and GaAs, is proposed to account for the abnormally fast Ga vacancy diffusion inside the heterostructure. A spatial control of the interdiffused areas can be achieved if a suitable stress field is imposed on the semiconductor surface by the capping layers. We show experimental evidence of this effect using a specific patterning of SiO2/Si3N4 bilayers.

Amplification Path Length Dependence Studies of Stimulated Emission from Optically Pumped InGaN/GaN Multiple Quantum Wells

1998 ◽  
Vol 537 ◽  
Author(s):  
T.J. Schmidt ◽  
S. Bidnyk ◽  
Yong-Hoon Cho ◽  
A.J. Fischer ◽  
J.J. Song ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Chemical Vapor ◽  
High Energy ◽  
Stimulated Emission ◽  
Multiple Quantum Wells ◽  
Excitation Density ◽  
Multiple Quantum ◽  
Optically Pumped ◽  
Energy Peak ◽  
The Difference

AbstractOptically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (Lexc). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high energy peak was observed to always be lower than that of the low energy peak, but the difference was found to decrease greatly with increasing Lexc. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region.

scholarly journals Amplification Path Length Dependence Studies of Stimulated Emission from Optically Pumped InGaN/GaN Multiple Quantum Wells

1999 ◽  
Vol 4 (S1) ◽  
pp. 757-762 ◽  
Author(s):  
T.J. Schmidt ◽  
S. Bidnyk ◽  
Yong-Hoon Cho ◽  
A.J. Fischer ◽  
J.J. Song ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Chemical Vapor ◽  
High Energy ◽  
Stimulated Emission ◽  
Multiple Quantum Wells ◽  
Excitation Density ◽  
Multiple Quantum ◽  
Optically Pumped ◽  
Energy Peak ◽  
The Difference

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (Lexc). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high energy peak was observed to always be lower than that of the low energy peak, but the difference was found to decrease greatly with increasing Lexc. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region.

Si3 N4/SiO2 Multi-Layer Reflecting Stacks for Photonic Switching Applications

1993 ◽  
Vol 298 ◽  
Author(s):  
D.J. Stephens ◽  
S.S. He ◽  
G. Lucovsky ◽  
H. Mikkelsen ◽  
K. Leo
Keyword(s):  
Optical Properties ◽  
Periodic Structures ◽  
Chemical Vapor ◽  
Optical Path Length ◽  
High Energy ◽  
Fused Silica ◽  
Nitride Film ◽  
Photonic Switching ◽  
Model Calculations ◽  
Nitride Layers

AbstractWe have fabricated stacked-structures comprised of i) fused silica substrates, and ii) near-periodic Si3N4/SiO2 bi-layers by low-temperature, 250°C, remote plasmaenhanced chemical-vapor deposition. Comparing the reflectance of these structures with model calculations, we have been able to identify the effects on the reflectance spectra of departures from i) exact periodicity, ii) not having the constituent dielectric layers each posses an ideal optical path length, OPL, exactly equal to λcentral/4, and iii) the intrinsic dispersion in the dielectric functions of the oxide and nitride materials. We have prepared quasi-periodic structures in which the OPL of the higher index Si3N4 layer was > λcentral/4, and in which the OPL of the lower index SiO2 layer was < λcentral/4. This promotes a second strong reflectance band at an energy that is approximately two times that of the primary band. Calculations have shown that the reflectance values in this band, and near a reflectance minimum on the high energy side of the band, are both very sensitive to changes in the optical properties of the nitride film. We present calculations that demonstrate the effects on the reflectance of this band by a temperature-induced modulation of the optical properties of the oxide and nitride layers.

Defects in β-SiC thin films grown on α-SiC substrates

1988 ◽  
Vol 46 ◽  
pp. 568-569
Author(s):  
Karren L. More
Keyword(s):  
Thin Films ◽  
Semiconductor Device ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Substrate Material ◽  
Growth Interface ◽  
Si Substrates ◽  
Thermal Expansion Coefficients ◽  
Device Applications ◽  
Expansion Coefficients

Beta-SiC is an ideal candidate material for use in semiconductor device applications. Currently, monocrystalline β-SiC thin films are epitaxially grown on {100} Si substrates by chemical vapor deposition (CVD). These films, however, contain a high density of defects such as stacking faults, microtwins, and antiphase boundaries (APBs) as a result of the 20% lattice mismatch across the growth interface and an 8% difference in thermal expansion coefficients between Si and SiC. An ideal substrate material for the growth of β-SiC is α-SiC. Unfortunately, high purity, bulk α-SiC single crystals are very difficult to grow. The major source of SiC suitable for use as a substrate material is the random growth of {0001} 6H α-SiC crystals in an Acheson furnace used to make SiC grit for abrasive applications. To prepare clean, atomically smooth surfaces, the substrates are oxidized at 1473 K in flowing 02 for 1.5 h which removes ∽50 nm of the as-grown surface. The natural {0001} surface can terminate as either a Si (0001) layer or as a C (0001) layer.

scholarly journals Effects of Recycled Fe2O3 Nanofiller on the Structural, Thermal, Mechanical, Dielectric, and Magnetic Properties of PTFE Matrix

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2332
Author(s):  
Ahmad Mamoun Khamis ◽  
Zulkifly Abbas ◽  
Raba’ah Syahidah Azis ◽  
Ebenezer Ekow Mensah ◽  
Ibrahim Abubakar Alhaji
Keyword(s):  
Electron Microscopy ◽  
High Energy ◽  
Filler Loading ◽  
Complex Permeability ◽  
X Ray Diffraction ◽  
Thermal Expansion Coefficients ◽  
Transmission Electron ◽  
Energy Ball ◽  
Hematite Fe2o3 ◽  
Ptfe Composites

The purpose of this study was to improve the dielectric, magnetic, and thermal properties of polytetrafluoroethylene (PTFE) composites using recycled Fe2O3 (rFe2O3) nanofiller. Hematite (Fe2O3) was recycled from mill scale waste and the particle size was reduced to 11.3 nm after 6 h of high-energy ball milling. Different compositions (5–25 wt %) of rFe2O3 nanoparticles were incorporated as a filler in the PTFE matrix through a hydraulic pressing and sintering method in order to fabricate rFe2O3–PTFE nanocomposites. The microstructure properties of rFe2O3 nanoparticles and the nanocomposites were characterized through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The thermal expansion coefficients (CTEs) of the PTFE matrix and nanocomposites were determined using a dilatometer apparatus. The complex permittivity and permeability were measured using rectangular waveguide connected to vector network analyzer (VNA) in the frequency range 8.2–12.4 GHz. The CTE of PTFE matrix decreased from 65.28×10−6/°C to 39.84×10−6/°C when the filler loading increased to 25 wt %. The real (ε′) and imaginary (ε″) parts of permittivity increased with the rFe2O3 loading and reached maximum values of 3.1 and 0.23 at 8 GHz when the filler loading was increased from 5 to 25 wt %. A maximum complex permeability of 1.1−j0.07 was also achieved by 25 wt % nanocomposite at 10 GHz.

Mirror to measure small angle x-ray scattering signal in high energy density experiments

2020 ◽  
Vol 91 (12) ◽  
pp. 123501
Author(s):  
M. Šmíd ◽  
C. Baehtz ◽  
A. Pelka ◽  
A. Laso García ◽  
S. Göde ◽  
...  
Keyword(s):  
Energy Density ◽  
Small Angle ◽  
High Energy ◽  
High Energy Density ◽  
X Ray ◽  
X Ray Scattering ◽  
Scattering Signal ◽  
Ray Scattering

scholarly journals Investigations on the Optical Properties of InGaN/GaN Multiple Quantum Wells with Varying GaN Cap Layer Thickness

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Xiaowei Wang ◽  
Feng Liang ◽  
Degang Zhao ◽  
Zongshun Liu ◽  
Jianjun Zhu ◽  
...  
Keyword(s):  
Optical Properties ◽  
Quantum Wells ◽  
Layer Thickness ◽  
Stark Effect ◽  
Chemical Vapor ◽  
Multiple Quantum ◽  
Three Samples ◽  
Measurement Results ◽  
Cap Layer ◽  
The Difference

Abstract Three InGaN/GaN MQWs samples with varying GaN cap layer thickness were grown by metalorganic chemical vapor deposition (MOCVD) to investigate the optical properties. We found that a thicker cap layer is more effective in preventing the evaporation of the In composition in the InGaN quantum well layer. Furthermore, the quantum-confined Stark effect (QCSE) is enhanced with increasing the thickness of GaN cap layer. In addition, compared with the electroluminescence measurement results, we focus on the difference of localization states and defects in three samples induced by various cap thickness to explain the anomalies in room temperature photoluminescence measurements. We found that too thin GaN cap layer will exacerbates the inhomogeneity of localization states in InGaN QW layer, and too thick GaN cap layer will generate more defects in GaN cap layer.

Influence of Magnetoelastic Anisotropy on Properties of Nanostructured Microwires

2013 ◽  
Vol 646 ◽  
pp. 59-66 ◽  
Author(s):  
Arcady Zhukov ◽  
Margarita Churyukanova ◽  
Lorena Gonzalez-Legarreta ◽  
Ahmed Talaat ◽  
Valentina Zhukova ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Hysteresis Loops ◽  
Magnetic Behaviour ◽  
Soft Magnetic ◽  
Magnetoelastic Anisotropy ◽  
Thermal Expansion Coefficients ◽  
Magnetoelastic Energy ◽  
Expansion Coefficients ◽  
The Difference ◽  
Magneto Resistance

We studied the effect ofthe magnetoelastic ansitropy on properties of nanostructured glass-coated microwires with soft magnetic behaviour (Finemet-type microwires of Fe70.8Cu1Nb3.1Si14.5B10.6, Fe71.8Cu1Nb3.1Si15B9.1 and Fe73.8Cu1Nb3.1Si13B9.1 compositions) and with granular structure (Cu based Co-Cu microwires). The magnetoelastic energy originated from the difference in thermal expansion coefficients of the glass and metallic alloy during the microwires fabrication, affected the hysteresis loops, coercivity and heat capacity of Finemet-type microwires. Hysteresis loops of all as-prepared microwires showed rectangular shape, typical for Fe-rich microwires. As expected, coercivity, HC, of as-prepared microwires increases with decreasing of the ratio ρ defined as the ratio between the metallic nucleus diameter, d to total microwire diameter, D. On the other hand we observed change of heat capacity in microwires with different ratio ρ. In the case of Co-Cu microwires ρ- ratio affected the structure and the giant magneto-resistance of obtained microwires.

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