scholarly journals Intensity of Radiative Recombination in the Germanium/Silicon Nanosystem with Germanium Quantum Dots

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 275
Author(s):  
Sergey I. Pokutnyi ◽  
Lucjan Jacak
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Radiative Recombination ◽  
Electron Transition ◽  
Real Space ◽  
Bandgap Energy ◽  
Silicon Matrix ◽  
Hole Energy ◽  
Germanium Quantum Dots ◽  
Germanium Silicon

It is shown that in a germanium/silicon nanosystem with germanium quantum dots, the hole leaving the germanium quantum dot causes the appearance of the hole energy level in the bandgap energy in a silicon matrix. The dependences of the energies of the ground state of a hole and an electron are obtained as well as spatially indirect excitons on the radius of the germanium quantum dot and on the depth of the potential well for holes in the germanium quantum dot. It is found that as a result of a direct electron transition in real space between the electron level that is located in the conduction band of the silicon matrix and the hole level located in the bandgap of the silicon matrix, the radiative recombination intensity in the germanium/silicon nanosystem with germanium quantum dots increases significantly.

scholarly journals Electron tunneling in the germanium/silicon heterostructure with germanium quantum dots: theory

2021 ◽  
Vol 12 (4) ◽  
pp. 306-313
Author(s):  
S. I. Pokutnyi ◽  
◽  
N. G. Shkoda ◽  
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Electron Tunneling ◽  
Infrared Range ◽  
Silicon Matrix ◽  
Electron States ◽  
A Chain ◽  
A Charge ◽  
Germanium Quantum Dots ◽  
Germanium Silicon

It is shown that electron tunneling through a potential barrier that separates two quantum dots of germanium leads to the splitting of electron states localized over spherical interfaces (a quantum dot – a silicon matrix). The dependence of the splitting values of the electron levels on the parameters of the nanosystem (the radius a quantum dot germanium, as well as the distance D between the surfaces of the quantum dots) is obtained. It has been shown that the splitting of electron levels in the QD chain of germanium causes the appearance of a zone of localized electron states, which is located in the bandgap of silicon matrix. It has been found that the motion of a charge-transport exciton along a chain of quantum dots of germanium causes an increase in photoconductivity in the nanosystem. It is shown that in the QD chain of germanium a zone of localized electron states arises, which is located in the bandgap of the silicon matrix. Such a zone of local electron states is caused by the splitting of electron levels in the QD chain of germanium. Moreover, the motion of an electron in the zone of localized electron states causes an increase in photoconductivity in the nanosystem. The effect of increasing photoconductivity can make a significant contribution in the process of converting the energy of the optical range in photosynthesizing nanosystems. It has been found that comparison of the splitting dependence of the exciton level Eех(а) at a certain radius a QD with the experimental value of the width of the zone of localized electron states arising in the QD chain of germanium, allows us to obtain the distances D between the QD surfaces. It has been shown that by changing the parameters of Ge/Si heterostructures with germanium QDs (radius of a germanium QD, as well as the distance D between the surfaces of the QDs), it is possible to vary the positions and widths of the zones of localized electronic states. The latter circumstance opens up new possibilities in the use of such nanoheterostructures as new structural materials for the creation of new nano-optoelectronics and nano-photosynthesizing devices of the infrared range.

Quantum Confinement in the Spectral Response of n-Doped Germanium Quantum Dots Embedded in an Amorphous Si Layer for Quantum Dot-Based Solar Cells

2020 ◽  
Vol 3 (3) ◽  
pp. 2813-2821
Author(s):  
Jacopo Parravicini ◽  
Francesco Di Trapani ◽  
Michael D. Nelson ◽  
Zachary T. Rex ◽  
Ryan D. Beiter ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Solar Cells ◽  
Quantum Dot ◽  
Quantum Confinement ◽  
Spectral Response ◽  
Amorphous Si ◽  
Germanium Quantum Dots

Plasmon–exciton interaction strongly increases the efficiency of a quantum dot–based near-infrared photodetector operating in the two-photon absorption mode under normal conditions.

Nanoscale ◽  
2021 ◽  
Author(s):  
Victor A. Krivenkov ◽  
Pavel Samokhvalov ◽  
Ivan Vasil’evskii ◽  
Nikolai Kargin ◽  
Igor Nabiev
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Near Infrared ◽  
Semiconductor Quantum Dots ◽  
Photon Absorption ◽  
Bandgap Energy ◽  
Infrared Photodetector ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Absorption Mode

Semiconductor quantum dots (QDs) are known for their high two-photon absorption (TPA) capacity. This allows them to efficiently absorb infrared photons with energies lower than the bandgap energy. Moreover, TPA...

Solar Cells Based on Quantum Dots: Multiple Exciton Generation and Intermediate Bands

MRS Bulletin ◽  
2007 ◽  
Vol 32 (3) ◽  
pp. 236-241 ◽  
Author(s):  
Antonio Luque ◽  
Antonio Martí ◽  
Arthur J. Nozik
Keyword(s):  
Quantum Dots ◽  
Solar Cells ◽  
Quantum Dot ◽  
Single Photon ◽  
Quantum Yields ◽  
Bandgap Energy ◽  
Hot Electron ◽  
Electron Hole ◽  
Multiple Exciton Generation ◽  
Intermediate Band

AbstractSemiconductor quantum dots may be used in so-called third-generation solar cells that have the potential to greatly increase the photon conversion efficiency via two effects: (1) the production of multiple excitons from a single photon of sufficient energy and (2) the formation of intermediate bands in the bandgap that use sub-bandgap photons to form separable electron–hole pairs. This is possible because quantization of energy levels in quantum dots produces the following effects: enhanced Auger processes and Coulomb coupling between charge carriers; elimination of the requirement to conserve crystal momentum; slowed hot electron–hole pair (exciton) cooling; multiple exciton generation; and formation of minibands (delocalized electronic states) in quantum dot arrays. For exciton multiplication, very high quantum yields of 300–700% for exciton formation in PbSe, PbS, PbTe, and CdSe quantum dots have been reported at photon energies about 4–8 times the HOMO–LUMO transition energy (quantum dot bandgap), respectively, indicating the formation of 3–7 excitons/photon, depending upon the photon energy. For intermediate-band solar cells, quantum dots are used to create the intermediate bands from the con fined electron states in the conduction band. By means of the intermediate band, it is possible to absorb below-bandgap energy photons. This is predicted to produce solar cells with enhanced photocurrent without voltage degradation.

scholarly journals Quantum Dot-like Plasmonic Modes in Twisted Bilayer Graphene Supercells

2D Materials ◽  
2021 ◽  
Author(s):  
T. Westerhout ◽  
Mikhail I Katsnelson ◽  
Malte Rösner
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Random Phase ◽  
System Size ◽  
High Energy ◽  
Bilayer Graphene ◽  
Real Space ◽  
Local Background ◽  
Twisted Bilayer Graphene ◽  
Twisting Angle

Abstract We derive a material-realistic real-space many-body Hamiltonian for twisted bilayer graphene from first principles, including both single-particle hopping terms for $p_z$ electrons and their long-range Coulomb interaction. By disentangling low- and high-energy subspaces of the electronic dispersion, we are able to utilize state-of-the-art constrained Random Phase Approximation calculations to reliably describe the non-local background screening from the high-energy $s$, $p_x$, and $p_y$ electron states which we find to be independent of the bilayer stacking and thus of the twisting angle. The twist-dependent low-energy screening from $p_z$ states is subsequently added to obtain a full screening model. We use this modeling scheme to study plasmons in electron-doped twisted bilayer graphene supercells. We find that the finite system size yields discretized plasmonic levels, which are controlled by the system size, doping level, and twisting angle. This tunability together with atomic-like charge distributions of some of the excitations renders these plasmonic excitations remarkably similar to the electronic states in electronic quantum dots. To emphasize this analogy in the following we refer to these supercells as \emph{plasmonic quantum dots}. Based on a careful comparison to pristine AB-stacked bilayer graphene plasmons, we show that two kinds of plasmonic excitations arise, which differ in their layer polarization. Depending on this layer polarization the resulting plasmonic quantum dot states are either significantly or barely dependent on the twisting angle. Due to their tunability and their coupling to light, these plasmonic quantum dots form a versatile and promising platform for tailored light-matter interactions.

scholarly journals Theoretical Study of One-Intermediate Band Quantum Dot Solar Cell

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Abou El-Maaty Aly ◽  
Ashraf Nasr
Keyword(s):  
Quantum Dots ◽  
Solar Cell ◽  
Quantum Dot ◽  
Power Conversion Efficiency ◽  
Conversion Efficiency ◽  
Power Conversion ◽  
Maximum Efficiency ◽  
Total Output ◽  
Bandgap Energy ◽  
Intermediate Band

The intermediate bands (IBs) between the valence and conduction bands play an important role in solar cells. Because the smaller energy photons than the bandgap energy can be used to promote charge carriers transfer to the conduction band and thereby the total output current increases while maintaining a large open circuit voltage. In this paper, the influence of the new band on the power conversion efficiency for the structure of the quantum dots intermediate band solar cell (QDIBSC) is theoretically investigated and studied. The time-independent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42% for simple cubic quantum dot crystal under full concentration light. It is strongly dependent on the width of quantum dots and barrier distances.

NiAg-graphene quantum dot-graphene hybrid with high oxidase-like catalytic activity for sensitive colorimetric detection of malathion

2021 ◽  
Author(s):  
Xu Dan ◽  
Ruiyi Li ◽  
Qinsheng Wang ◽  
Yongqiang Yang ◽  
Haiyan Zhu ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Graphene Oxide ◽  
Catalytic Activity ◽  
Quantum Dot ◽  
Colorimetric Detection ◽  
Graphene Quantum Dots ◽  
Functionalized Graphene ◽  
Graphene Quantum Dot ◽  
Nickel Silver

The paper reports the synthesis of nickel-silver-graphene quantum dot-graphene hybrid. Histidine-functionalized graphene quantum dots (His-GQDs) were bonded to graphene oxide (GO) and then combined with Ni2+ and Ag+ to form...

scholarly journals Effect of Growth Temperature on the Characteristics of CsPbI3-Quantum Dots Doped Perovskite Film

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4439
Author(s):  
Shui-Yang Lien ◽  
Yu-Hao Chen ◽  
Wen-Ray Chen ◽  
Chuan-Hsi Liu ◽  
Chien-Jung Huang
Keyword(s):  
Thin Films ◽  
Thermal Stability ◽  
Quantum Dots ◽  
Quantum Dot ◽  
Growth Temperature ◽  
Electron Mobility ◽  
Surface Defects ◽  
Different Temperatures ◽  
Pb Doping ◽  
Pristine Film

In this study, adding CsPbI3 quantum dots to organic perovskite methylamine lead triiodide (CH3NH3PbI3) to form a doped perovskite film filmed by different temperatures was found to effectively reduce the formation of unsaturated metal Pb. Doping a small amount of CsPbI3 quantum dots could enhance thermal stability and improve surface defects. The electron mobility of the doped film was 2.5 times higher than the pristine film. This was a major breakthrough for inorganic quantum dot doped organic perovskite thin films.

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