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Impact ionization

About: Impact ionization is a research topic. Over the lifetime, 4223 publications have been published within this topic receiving 74145 citations.


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TL;DR: In this article, three QD solar cell configurations are described: (1) photoelectrodes comprising QD arrays, (2) QD-sensitized nanocrystalline TiO 2, and (3) QDs dispersed in a blend of electron- and hole-conducting polymers.
Abstract: Quantum dot (QD) solar cells have the potential to increase the maximum attainable thermodynamic conversion efficiency of solar photon conversion up to about 66% by utilizing hot photogenerated carriers to produce higher photovoltages or higher photocurrents. The former effect is based on miniband transport and collection of hot carriers in QD array photoelectrodes before they relax to the band edges through phonon emission. The latter effect is based on utilizing hot carriers in QD solar cells to generate and collect additional electron–hole pairs through enhanced impact ionization processes. Three QD solar cell configurations are described: (1) photoelectrodes comprising QD arrays, (2) QD-sensitized nanocrystalline TiO 2 , and (3) QDs dispersed in a blend of electron- and hole-conducting polymers. These high-efficiency configurations require slow hot carrier cooling times, and we discuss initial results on slowed hot electron cooling in InP QDs.

2,405 citations

Journal ArticleDOI
TL;DR: It is demonstrated for the first time that impact ionization (II) (the inverse of Auger recombination) occurs with very high efficiency in semiconductor nanocrystals (NCs) and can be used to considerably increase the power conversion efficiency of NC-based solar cells.
Abstract: We demonstrate for the first time that impact ionization (II) (the inverse of Auger recombination) occurs with very high efficiency in semiconductor nanocrystals (NCs). Interband optical excitation of PbSe NCs at low pump intensities, for which less than one exciton is initially generated per NC on average, results in the formation of two or more excitons (carrier multiplication) when pump photon energies are more than 3 times the NC band gap energy. The generation of multiexcitons from a single photon absorption event is observed to take place on an ultrafast (picosecond) time scale and occurs with up to 100% efficiency depending upon the excess energy of the absorbed photon. Efficient II in NCs can be used to considerably increase the power conversion efficiency of NC-based solar cells.

1,732 citations

Journal ArticleDOI
D. Du, X. Liu, Georg Korn, Jeff Squier, Gerard Mourou 
TL;DR: In this article, the results of laser-induced breakdown experiments in fused silica (SiO2) employing 150 fs −7 ns, 780 nm laser pulses are reported and the avalanche ionization mechanism is found to dominate over the entire pulse width range.
Abstract: Results of laser‐induced breakdown experiments in fused silica (SiO2) employing 150 fs–7 ns, 780 nm laser pulses are reported. The avalanche ionization mechanism is found to dominate over the entire pulse‐width range. Fluence breakdown threshold does not follow the scaling of Fth∼ √τp, when pulses are shorter than 10 ps. The impact ionization coefficient of SiO2 is measured up to ∼3×108 V/cm. The relative role of photoionization in breakdown for ultrashort pulses is discussed.

848 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed a simple phenomenological model capable of describing the present experimental situation from the standpoint of yield, variance, and bandgap dependence, based on the premise that e, the average amount of radiation energy consumed per pair, can be accounted for by a sum of three contributions: the intrinsic bandgap (EG), optical phonon losses r(ℏωR), and the residual kinetic energy (9/5) EG.
Abstract: The problems dealt with concern the production of electron‐hole pairs in a semiconductor exposed to high‐energy radiation. The goal is to develop a simple phenomenological model capable of describing the present experimental situation from the standpoint of yield, variance, and bandgap dependence. We proceed on the premise that e, the average amount of radiation energy consumed per pair, can be accounted for by a sum of three contributions: the intrinsic bandgap (EG), optical phonon losses r(ℏωR), and the residual kinetic energy (9/5) EG. The approach differs from prior treatments in the sense that the residual kinetic energy relates to a threshold for impact ionization taken to be 32EG in accordance with indications stemming from studies of avalanching in p‐n junctions. This model is subjected to three quantitative tests: (a) Fano‐factor variations are found to reflect the relative weight of phonon losses [K=r(ℏωR)/EG], but residual energy fluctuations govern the statistical behavior for K2 ≲0.3. An appl...

702 citations

Journal ArticleDOI
TL;DR: In this article, two mechanisms triggered by electron heating in the oxide conduction band are discussed: trap creation and band gap ionization by carriers with energies exceeding 2 and 9 eV, respectively.
Abstract: Degradation of silicon dioxide films is shown to occur primarily near interfaces with contacting metals or semiconductors. This deterioration is shown to be accountable through two mechanisms triggered by electron heating in the oxide conduction band. These mechanisms are trap creation and band‐gap ionization by carriers with energies exceeding 2 and 9 eV with respect to the bottom of the oxide conduction band, respectively. The relationship of band‐gap ionization to defect production and subsequent degradation is emphasized. The dependence of the generated sites on electric field, oxide thickness, temperature, voltage polarity, and processing for each mechanism is discussed. A procedure for separating and studying these two generation modes is also discussed. A unified model from simple kinetic relationships is developed and compared to the experimental results. Destructive breakdown of the oxide is shown to be correlated with ‘‘effective’’ interface softening due to the total defect generation caused by both mechanisms.

682 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202330
202274
202192
2020115
2019101
2018101