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237 results on '"Ware, Morgan E"'

1. Modeling of V graded In(x)Ga(1-x)N solar cells: comparison of strained and relaxed features

Author

Sarollahi, Mirsaeid, Alavijeh, Mohammad Zamani, Allaparthi, Rohith, Alhelais, Reem, Refaei, Malak A., Maruf, Md Helal Uddin, and Ware, Morgan E.

Subjects
Condensed Matter - Materials Science, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

The optical properties of V graded InGaN solar cells are studied. Graded InGaN well structures with the indium composition increasing then decreasing in a V shaped pattern have been designed. Through polarization doping, this naturally creates alternating p-type and n-type regions. Separate structures are designed by varying the indium alloy profile from GaN to maximum indium concentrations ranging from 20% to 80%, while maintaining a constant overall structure thicknesses of 100 nm. The solar cell parameters under fully strained and relaxed conditions are considered. The results show that a maximum efficiency of 5.5%, under fully strained condition occurs at x=60%. Solar cell efficiency under relaxed conditions increases to a maximum of 8.3% at 90%. While Vegards law predicts the bandgap under relaxed conditions, a Vegard like law is empirically determined from the output of Nextnano for varying In compositions in order to calculate solar cell parameters under strain., Comment: This simulation work was done by Nextnano+ and Matlab. 20 pages, 13 Figures

Published
2022

4. Study of simulations of double graded InGaN solar cell structures

Author

Sarollahi, Mirsaeid, Aldawsari, Manal A., Allaparthi, Rohith, Refaei, Malak A., Alhelais, Reem, Maruf, Md Helal Uddin, Mazur, Yuriy, and Ware, Morgan E.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

The performances of various configurations of InGaN solar cells are compared using nextnano software. Here we compare a flat base graded wall GaN/InGaN structure, with an InxGa1-xN well with sharp GaN contact layers, and an InxGa1-xN structure with InxGa1-xN contact layers, i.e. a homojunction. The doping in the graded structures are the result of polarization doping at each edge (10 nm from each side) due to the graded structure, while the well structures are intentionally doped at each edge (10 nm from each side) equal to the doping concentration in the graded structure. The solar cells are characterized by their open-circuit voltage, V_oc, short circuit current, I_sc, solar efficiency, and energy band diagram. The results indicate that an increase in I_sc and efficiency results from increasing both the fixed and the maximum indium compositions, while the V_oc decreases. The maximum efficiency is obtained for the InGaN well with 60% In., Comment: 14 pages, 12 figures

Published
2021
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31. Photoluminescence Characterization of Interlayer Carrier Injection from Ingaas Quantum Well to Ingaas Surface Quantum Dots with Respect to Gaas Spacer Thickness

Author

Liu, Jingtao, primary, Li, Hang, additional, Liu, Xiaohui, additional, Wang, Ying, additional, Guo, Yingnan, additional, Wang, Shufang, additional, Fu, Guangsheng, additional, Mazur, Yu.I., additional, Ware, Morgan E., additional, Salamo, G. J., additional, and Liang, Baolai, additional

Published
2023
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35. Modeling of temperature dependence of Λ-graded InGaN solar cells for both strained and relaxed features

Author

Sarollahi, Mirsaeid, Zamani-Alavijeh, Mohammad, Aldawsari, Manal A., Allaparthi, Rohith, Maruf, Md Helal Uddin, Refaei, Malak, Alhelais, Reem, Mazur, Yuriy I., and Ware, Morgan E.

Subjects
Materials Science (miscellaneous)
Abstract

The temperature dependence of Λ-graded InGaN solar cells is studied through simulation using nextnano software. Λ-Graded structures have been designed by increasing and then decreasing the indium composition in epitaxial InGaN layers. Due to polarization doping, layers of p-type and n-type doping arise without the need for impurity doping. Different individual structures are designed by varying the indium alloy profile from GaN to maximum indium concentrations, xmax, ranging from 20% to 90% pseudomorphically strained to a GaN substrate and from 20% to 100% for completely strain-relaxed materials and linearly decreases back to GaN. For InxGa1-xN with x>∼0.9, if the material is strained to the GaN lattice constant, it is predicted to have a negative band gap. So this case is not considered here. The temperature dependence of the electrical and optical properties as they relate to the solar efficiency of the Λ-graded structures under relaxed and strained conditions are studied. Additionally, the dimensionless absorption coefficients are fitted and plotted as functions of the band gap under both strained and relaxed conditions at different temperatures. As a result, the generation rates as functions of the penetration depth within a cell can be calculated in order to obtain the solar cell parameters including efficiency for each Λ-graded structure at different temperatures. Under the strained condition, the xmax, where the solar cell efficiency reaches its maximum for each temperature, decreases as the temperature increases. At the same time, under the relaxed condition, at low temperatures (T = 100–400 K), xmax is 100%, that is, grading to InN results in maximum efficiency, while at higher temperatures (T = 500–800 K), xmax decreases with the increasing temperature.

Published
2022

38. Complex exciton dynamics with elevated temperature in a GaAsSb/GaAs quantum well heterostructure.

Author

Li, Hang, Wang, Ying, Guo, Yingnan, Wang, Shufang, Fu, Guangsheng, Mazur, Yuriy I., Ware, Morgan E., Salamo, Gregory J., and Liang, Baolai

Subjects
HIGH temperatures, QUANTUM wells, AUDITING standards, GALLIUM arsenide, EXCITON theory
Abstract

Exciton dynamics in a GaAsSb/GaAs quantum well (QW) heterostructure were investigated via both steady state and transient photoluminescence. The measurements at 10 K demonstrated the coexistence of localized excitons (LEs) and free excitons (FEs), while a blue-shift resulting from increased excitation intensity indicated their spatially indirect transition (IT) characteristics due to the type-II band alignment. With increasing temperature from 10 K, the LEs and FEs redistribute, with the LEs becoming less intense at relatively higher temperature. With increasing temperature to above 80 K, electrons in GaAs are able to overcome the small band offset to enter inside GaAsSb and recombine with holes; thus, a spatially direct transition (DT) appeared. Hence, we are able to reveal complex carrier recombination dynamics for the GaAsSb/GaAs QW heterostructure, in which the "S" shape behavior is generated not only by the carrier localization but also by the transformation from IT to DT with elevated temperature. [ABSTRACT FROM AUTHOR]

Published
2023
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39. Surface Atomic Arrangement of Aluminum Ultra-Thin Layers Grown on Si(111).

Author

Jum'h, Inshad, Abu-Safe, Husam H., Ware, Morgan E., Qattan, I. A., Telfah, Ahmad, and Tavares, Carlos J.

Subjects
X-ray photoelectron spectra, MOLECULAR beam epitaxy, X-ray photoelectron spectroscopy, ATOMIC force microscopy, SURFACE conductivity
Abstract

Surface atomic arrangement and physical properties of aluminum ultrathin layers on c-Si(111)-7 × 7 and hydrogen-terminated c-Si(111)-1 × 1 surfaces deposited using molecular beam epitaxy were investigated. X-ray photoelectron spectroscopy spectra were collected in two configurations (take-off angle of 0° and 45°) to precisely determine the surface species. Moreover, 3D atomic force microscopy (AFM) images of the air-exposed samples were acquired to investigate the clustering formations in film structure. The deposition of the Al layers was monitored in situ using a reflection high-energy electron diffraction (RHEED) experiments to confirm the surface crystalline structure of the c-Si(111). The analysis of the RHEED patterns during the growth process suggests the settlement of aluminum atoms in Al(111)-1 × 1 clustered formations on both types of surfaces. The surface electrical conductivity in both configurations was tested against atmospheric oxidation. The results indicate differences in conductivity based on the formation of various alloys on the surface. [ABSTRACT FROM AUTHOR]

Published
2023
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41. Type-II characteristics of photoluminescence from InGaAs/GaAs surface quantum dots due to Fermi level pinning effect

Author

Liu, Xiaohui, primary, Liu, Jingtao, additional, Liang, Baolai, additional, Wang, Ying, additional, Guo, Yingnan, additional, Wang, Chunsheng, additional, Wang, Shufang, additional, Fu, Guangsheng, additional, Mazur, Yuriy I., additional, Maidaniuk, Yurii, additional, Ware, Morgan E., additional, and Salamo, Gregory J., additional

Published
2022
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44. Excitation intensity and thickness dependent emission mechanism from an ultrathin InAs layer in GaAs matrix.

Author

Kumar, Rahul, Maidaniuk, Yurii, Kuchuk, Andrian, Saha, Samir K., Ghosh, Pijush K., Mazur, Yuriy I., Ware, Morgan E., and Salamo, Gregory J.

Subjects
INCIDENT radiation intensity, EPITAXY, MOLECULAR beams, PHOTOLUMINESCENCE, OPTICAL properties
Abstract

A set of samples containing a single ultrathin InAs layer with varying thickness from 0.5 to 1.4ML in a GaAs matrix have been grown by molecular beam epitaxy on GaAs (001) substrates at low temperatures and investigated by low-temperature photoluminescence (PL). A linear change in emission energy with InAs thickness has been experimentally observed. The PL emission line shape from InAs/GaAs heterostructures has been investigated as a function of incident optical intensity. The interplay between uncorrelated electron-hole pairs, free excitons, and localized excitons, as a function of the excitation intensity, is found to play a significant role on the optical properties of the InAs layer and is described in detail. [ABSTRACT FROM AUTHOR]

Published
2018
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