Understanding Nonradiative Recombination through Defect-Induced Conical Intersections

2017 ◽  
Vol 8 (17) ◽  
pp. 4091-4099 ◽  
Author(s):  
Yinan Shu ◽  
B. Scott Fales ◽  
Wei-Tao Peng ◽  
Benjamin G. Levine
Keyword(s):  
Nonradiative Recombination ◽  
Conical Intersections

Locality of conical intersections in semiconductor nanomaterials

2019 ◽  
Vol 21 (21) ◽  
pp. 10870-10878 ◽  
Author(s):  
Benjamin G. Levine ◽  
Wei-Tao Peng ◽  
Michael P. Esch
Keyword(s):  
Semiconductor Nanoparticles ◽  
Nonradiative Recombination ◽  
Conical Intersections ◽  
Semiconductor Nanomaterials

We review recent efforts to model nonradiative recombination in semiconductor nanoparticles through conical intersections, focusing on the reasons for and consequences of the locality of such intersections.

scholarly journals Conical Intersections at the Nanoscale: Molecular Ideas for Materials

2019 ◽  
Vol 70 (1) ◽  
pp. 21-43 ◽  
Author(s):  
Benjamin G. Levine ◽  
Michael P. Esch ◽  
B. Scott Fales ◽  
Dylan T. Hardwick ◽  
Wei-Tao Peng ◽  
...  
Keyword(s):  
Materials Science ◽  
Theoretical Study ◽  
Nonradiative Recombination ◽  
Conical Intersections ◽  
Computational Tools ◽  
Recent Developments ◽  
Semiconductor Nanomaterials ◽  
Identification And Characterization ◽  
Nonradiative Processes

The ability to predict and describe nonradiative processes in molecules via the identification and characterization of conical intersections is one of the greatest recent successes of theoretical chemistry. Only recently, however, has this concept been extended to materials science, where nonradiative recombination limits the efficiencies of materials for various optoelectronic applications. In this review, we present recent advances in the theoretical study of conical intersections in semiconductor nanomaterials. After briefly introducing conical intersections, we argue that specific defects in materials can induce conical intersections between the ground and first excited electronic states, thus introducing pathways for nonradiative recombination. We present recent developments in theoretical methods, computational tools, and chemical intuition for the prediction of such defect-induced conical intersections. Through examples in various nanomaterials, we illustrate the significance of conical intersections for nanoscience. We also discuss challenges facing research in this area and opportunities for progress.

Defect-Induced Conical Intersections Promote Nonradiative Recombination

Nano Letters ◽  
2015 ◽  
Vol 15 (9) ◽  
pp. 6247-6253 ◽  
Author(s):  
Yinan Shu ◽  
B. Scott Fales ◽  
Benjamin G. Levine
Keyword(s):  
Nonradiative Recombination ◽  
Conical Intersections

Influence of MBE Growth Conditions on Dislocation Densities of GaAs/Ge Epilayers Grown on Silicon Substrates

1985 ◽  
Vol 43 ◽  
pp. 364-365
Author(s):  
K.M. Hones ◽  
P. Sheldon ◽  
B.G. Yacobi ◽  
A. Mason
Keyword(s):  
High Efficiency ◽  
Lattice Mismatch ◽  
Low Cost ◽  
Growth Conditions ◽  
Nonradiative Recombination ◽  
Device Structure ◽  
Si Substrates ◽  
Transmission Electron ◽  
Dislocation Densities ◽  
Dislocation Type

There is increasing interest in growing epitaxial GaAs on Si substrates. Such a device structure would allow low-cost substrates to be used for high-efficiency cascade- junction solar cells. However, high-defect densities may result from the large lattice mismatch (∼4%) between the GaAs epilayer and the silicon substrate. These defects can act as nonradiative recombination centers that can degrade the optical and electrical properties of the epitaxially grown GaAs. For this reason, it is important to optimize epilayer growth conditions in order to minimize resulting dislocation densities. The purpose of this paper is to provide an indication of the quality of the epitaxially grown GaAs layers by using transmission electron microscopy (TEM) to examine dislocation type and density as a function of various growth conditions. In this study an intermediate Ge layer was used to avoid nucleation difficulties observed for GaAs growth directly on Si substrates. GaAs/Ge epilayers were grown by molecular beam epitaxy (MBE) on Si substrates in a manner similar to that described previously.

Low-Temperature Operation of Green, Blue and UV InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes

2003 ◽  
Vol 764 ◽  
Author(s):  
X. A. Cao ◽  
S. F. LeBoeuf ◽  
J. L. Garrett ◽  
A. Ebong ◽  
L. B. Rowland ◽  
...  
Keyword(s):  
Quantum Well ◽  
Light Emitting Diodes ◽  
Multiple Quantum Well ◽  
Light Output ◽  
Localized States ◽  
Multiple Quantum ◽  
Nonradiative Recombination ◽  
Light Emitting ◽  
Temperature Range ◽  
Green Leds

Absract:Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission energies ranging from 2.3 eV (green) to 3.3 eV (UV) has been studied over a wide temperature range (5-300 K). As the temperature is decreased from 300 K to 150 K, the EL intensity increases in all devices due to reduced nonradiative recombination and improved carrier confinement. However, LED operation at lower temperatures (150-5 K) is a strong function of In ratio in the active layer. For the green LEDs, emission intensity increases monotonically in the whole temperature range, while for the blue and UV LEDs, a remarkable decrease of the light output was observed, accompanied by a large redshift of the peak energy. The discrepancy can be attributed to various amounts of localization states caused by In composition fluctuation in the QW active regions. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED. The large number of localized states in the green LEDs are crucial to maintain high-efficiency carrier capture at low temperatures.

scholarly journals The Effect of Nitrogen Incorporation on the Optical Properties of Si-Rich a-SiCx Films Deposited by VHF PECVD

Micromachines ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 637
Author(s):  
Hongliang Li ◽  
Zewen Lin ◽  
Yanqing Guo ◽  
Jie Song ◽  
Rui Huang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Near Infrared ◽  
Chemical Vapor ◽  
Wide Bandgap ◽  
Nonradiative Recombination ◽  
Very High Frequency ◽  
N Content ◽  
High Frequency Plasma ◽  
Frequency Plasma ◽  
N Incorporation

The influence of N incorporation on the optical properties of Si-rich a-SiCx films deposited by very high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) was investigated. The increase in N content in the films was found to cause a remarkable enhancement in photoluminescence (PL). Relative to the sample without N incorporation, the sample incorporated with 33% N showed a 22-fold improvement in PL. As the N content increased, the PL band gradually blueshifted from the near-infrared to the blue region, and the optical bandgap increased from 2.3 eV to 5.0 eV. The enhancement of PL was suggested mainly from the effective passivation of N to the nonradiative recombination centers in the samples. Given the strong PL and wide bandgap of the N incorporated samples, they were used to further design an anti-counterfeiting label.

scholarly journals Role of Conical Intersections on the Efficiency of Fluorescent Organic Molecular Crystals

2021 ◽  
Vol 125 (4) ◽  
pp. 1012-1024
Author(s):  
Miguel Rivera ◽  
Ljiljana Stojanović ◽  
Rachel Crespo-Otero
Keyword(s):  
Molecular Crystals ◽  
Conical Intersections ◽  
Organic Molecular Crystals
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