scholarly journals Optical phonons and free-carrier effects in MOVPE grown AlxGa1−xN measured by Infrared Ellipsometry

1999 ◽  
Vol 4 (1) ◽  
Author(s):  
M. Schubert ◽  
A. Kasic ◽  
T.E. Tiwald ◽  
J. Off ◽  
B. Kuhn ◽  
...  
Keyword(s):  
Dispersion Model ◽  
Free Carrier ◽  
Model Parameters ◽  
Model Calculations ◽  
Group Iii ◽  
Infrared Ellipsometry ◽  
Mode Behavior ◽  
Novel Approach ◽  
Back Ground ◽  
Group Iii Nitride

We report on the application of infrared spectroscopic ellipsometry (IR-SE) for wavenumbers from 333cm−1 to 1200cm−1 as a novel approach to non-destructive optical characterization of free-carrier and optical phonon properties of group III-nitride heterostructures. Undoped α-GaN, α-AlN, α-AlxGa1−xN (x = 0.17, 0.28, 0.5), and n-type silicon (Si) doped α-GaN layers were grown by metal-organic vapor phase epitaxy (MOVPE) on c-plane sapphire (α-Al2O3). The four-parameter semi-quantum (FPSQ) dielectric lattice-dispersion model and the Drude model for free-carrier response are employed for analysis of the IR-SE data. Model calculations for the ordinary (∈⊥) and extraordinary (∈||) dielectric functions of the heterostructure components provide sensitivity to IR-active phonon frequencies and free-carrier parameters. We observe that the α-AlxGa1−xN layers are unintentionally doped with a back ground free-carrier concentration of 1–4 1018cm−3. The ternary compounds reveal a two-mode behavior in ∈⊥, whereas a one-mode behavior is sufficient to explain the optical response for ∈||. We further provide a precise set of model parameters for calculation of the sapphire infrared dielectric functions which are prerequisites for analysis of infrared spectra of III-nitride heterostructures grown on α-Al2O3.

Free-Carrier Response and Lattice Modes of Group III-Nitride Heterostructures Measured by Infrared Ellipsometry

1999 ◽  
Vol 216 (1) ◽  
pp. 655-658 ◽  
Author(s):  
M. Schubert ◽  
J.A. Woollam ◽  
A. Kasic ◽  
B. Rheinländer ◽  
J. Off ◽  
...  
Keyword(s):  
Free Carrier ◽  
Group Iii ◽  
Infrared Ellipsometry ◽  
Group Iii Nitride ◽  
Lattice Modes

scholarly journals Novel approach to simulation of group-III nitrides growth by MOVPE

1999 ◽  
Vol 4 (1) ◽  
Author(s):  
S. Yu. Karpov ◽  
V. G. Prokofyev ◽  
E. V. Yakovlev ◽  
R. A. Talalaev ◽  
Yu. N. Makarov
Keyword(s):  
Growth Process ◽  
Solid Phase ◽  
Molecular Nitrogen ◽  
Horizontal Tube ◽  
Group Iii Nitrides ◽  
Process Conditions ◽  
Group Iii ◽  
Novel Approach ◽  
Kinetic Effects ◽  
Group Iii Nitride

Recent studies revealed specific features of chemical processes occurring on the surface of growing group-III nitrides – extremely low sticking probability of molecular nitrogen, low sticking coefficient and incomplete decomposition of ammonia frequently used as the nitrogen precursor. These features (kinetic by nature) result in the growth process going on under conditions remarkably deviated from the gas-solid heterogeneous equilibrium. In this paper we propose a novel approach to modeling of group-III nitride growth by MOVPE taking into account these features. In the model the sticking/evaporation coefficients of N2 and NH3 extracted from independent experiments are used allowing adequate description of the kinetic effects. The model is applied to analysis of growth of binary (GaN) and ternary (InGaN) compounds in a horizontal tube reactor. The growth rate and the solid phase composition are predicted theoretically and compared with available experimental data. The modeling results reveal lower ammonia decomposition ratio on the surface of the crystal as compared to thermodynamic expectations. The developed model can be used for optimization of growth process conditions.

scholarly journals Properties of InN layers grown by High Pressure CVD

2006 ◽  
Vol 955 ◽  
Author(s):  
Mustafa Alevli ◽  
Goksel Durkaya ◽  
Ronny Kirste ◽  
Aruna Weesekara ◽  
Unil Perera ◽  
...  
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Growth Parameters ◽  
Free Carrier ◽  
Dielectric Constants ◽  
High Quality ◽  
Group Iii ◽  
High Efficient ◽  
Nitride Alloys ◽  
Group Iii Nitride

ABSTRACTIndium nitride (InN) and indium-rich group III-nitride alloys are promising materials for advanced optoelectronic device applications. Indium-rich alloys, e.g. (Ga1-y-xAlyInx)N will enable the fabrication of high-efficient light emitting diodes tunable in the whole visible spectral region, as well as advanced high speed optoelectronics for optical communication operating. The present limitation in this area is the growth of high quality InN and indium-rich group III-nitride alloys as documented in many controversial reports on the true physical properties of InN. The difficulties arise from the low dissociation temperature of InN that requires an extraordinarily high nitrogen overpressure to stabilize the material up to optimum growth temperatures. We developed a novel “high-pressure chemical vapor deposition” (HPCVD) system, capable to control and analyze the vast different partial pressures of the constituents. Our results show that the chosen HPCVD pathway leads to high-quality single crystalline InN, demonstrating that HPCVD is a viable tool for the growth of indium rich group III nitride alloys. The structural analysis of InN deposited on GaN-sapphire substrate by XRD show single phase InN(0002) peaks with full width half maximum (FWHM) around 400 arcsec. Infrared reflectance spectroscopy is used to analyze the plasmon frequencies, high frequency dielectric constants, the free carrier concentrations and carrier mobilities in these layers. For nominal undoped InN layers, free carrier concentrations in the mid 1019 cm−3 and mobilities around 600 cm−2-V-1-s-1 are observed. Further improvements are expected as the growth parameters are optimized. The explored growth parameters are close to of those employed for GaN growth conditions, which is a major step towards the fabrication of indium rich (Ga1−y−xAlyInx)N alloys and heterostructures.

scholarly journals Strong and robust polarization anisotropy of site- and size-controlled single InGaN/GaN quantum wires

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Hwan-Seop Yeo ◽  
Kwanjae Lee ◽  
Young Chul Sim ◽  
Seoung-Hwan Park ◽  
Yong-Hoon Cho
Keyword(s):  
Quantum Wire ◽  
Quantum Wires ◽  
Geometrical Shape ◽  
Optical Polarization ◽  
Polarization Anisotropy ◽  
Single Quantum ◽  
Group Iii ◽  
Highly Efficient ◽  
Group Iii Nitride ◽  
Size Controlled

Abstract Optical polarization is an indispensable component in photonic applications, the orthogonality of which extends the degree of freedom of information, and strongly polarized and highly efficient small-size emitters are essential for compact polarization-based devices. We propose a group III-nitride quantum wire for a highly-efficient, strongly-polarized emitter, the polarization anisotropy of which stems solely from its one-dimensionality. We fabricated a site-selective and size-controlled single quantum wire using the geometrical shape of a three-dimensional structure under a self-limited growth mechanism. We present a strong and robust optical polarization anisotropy at room temperature emerging from a group III-nitride single quantum wire. Based on polarization-resolved spectroscopy and strain-included 6-band k·p calculations, the strong anisotropy is mainly attributed to the anisotropic strain distribution caused by the one-dimensionality, and its robustness to temperature is associated with an asymmetric quantum confinement effect.

scholarly journals Explaining Neural Networks Using Attentive Knowledge Distillation

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1280
Author(s):  
Hyeonseok Lee ◽  
Sungchan Kim
Keyword(s):  
Neural Networks ◽  
Model Prediction ◽  
Saliency Map ◽  
Model Parameters ◽  
Learning Capability ◽  
Fine Grained ◽  
Network Layers ◽  
Saliency Maps ◽  
Novel Approach ◽  
Knowledge Distillation

Explaining the prediction of deep neural networks makes the networks more understandable and trusted, leading to their use in various mission critical tasks. Recent progress in the learning capability of networks has primarily been due to the enormous number of model parameters, so that it is usually hard to interpret their operations, as opposed to classical white-box models. For this purpose, generating saliency maps is a popular approach to identify the important input features used for the model prediction. Existing explanation methods typically only use the output of the last convolution layer of the model to generate a saliency map, lacking the information included in intermediate layers. Thus, the corresponding explanations are coarse and result in limited accuracy. Although the accuracy can be improved by iteratively developing a saliency map, this is too time-consuming and is thus impractical. To address these problems, we proposed a novel approach to explain the model prediction by developing an attentive surrogate network using the knowledge distillation. The surrogate network aims to generate a fine-grained saliency map corresponding to the model prediction using meaningful regional information presented over all network layers. Experiments demonstrated that the saliency maps are the result of spatially attentive features learned from the distillation. Thus, they are useful for fine-grained classification tasks. Moreover, the proposed method runs at the rate of 24.3 frames per second, which is much faster than the existing methods by orders of magnitude.

scholarly journals Influence of the variability of the odour emission rate on its impact range: a case study of the selected industrial source

2019 ◽  
Vol 100 ◽  
pp. 00070 ◽  
Author(s):  
Elżbieta Romanik ◽  
Yaroslav Bezyk ◽  
Marcin Pawnuk ◽  
Urszula Miller ◽  
Agnieszka Grzelka
Keyword(s):  
Emission Rate ◽  
Dispersion Model ◽  
Grid Size ◽  
Model Calculations ◽  
Gas Treatment ◽  
Industrial Source ◽  
Odour Concentration ◽  
Made In ◽  
Dynamic Olfactometry

Odour concentration measurements in a chosen industrial source were made in this study using the method of dynamic olfactometry. The two different scenarios considered the variation of the odour emission rate as input for the dispersion model were compared for the period 2017 (before installation of the equipment for gas treatment) and 2018 (after implementation of purifying technologies). In this paper the odour impact range was determined by applying model calculations conducted in the Polish reference dispersion model – OPERAT FB software for the grid size 2 x 2 km. The conducted research shows a significant improvement in the odour impact range of chosen industrial source in year 2018 compared to 2017.

NbN Capping Layer for Enhanced Thermal Processing of Group III-Nitride Semiconductor Devices

2016 ◽  
Vol 6 (2) ◽  
pp. Q3067-Q3070 ◽  
Author(s):  
J. D. Greenlee ◽  
A. Nath ◽  
T. J. Anderson ◽  
B. N. Feigelson ◽  
A. D. Koehler ◽  
...  
Keyword(s):  
Thermal Processing ◽  
Semiconductor Devices ◽  
Capping Layer ◽  
Group Iii ◽  
Nitride Semiconductor ◽  
Group Iii Nitride
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