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Related Concept Videos

Carrier Transport01:21

Carrier Transport

The generation of electrical current in semiconductors is fundamentally driven by two mechanisms: drift and diffusion. These processes are essential for the functionality and performance of semiconductor-based devices.
Drift Current:
The drift of charge carriers is started by an external electric field (E). Charged particles, such as electrons and holes, experience an acceleration between collisions with lattice atoms. For electrons, this results in a drift velocity (vd) given by:
Carrier Generation and Recombination01:22

Carrier Generation and Recombination

Carrier generation is the process by which electron-hole pairs (EHPs) are created within the semiconductor. In direct-bandgap semiconductors, such as gallium arsenide (GaAs), this occurs efficiently when energy absorption prompts valence electrons to leap into the conduction band, leaving behind holes.
This process is given by the generation rate G and is efficient due to the conservation of momentum between the valence band maximum and conduction band minimum.
Indirect generation involves an...
Electron Carriers01:24

Electron Carriers

Electron carriers can be thought of as electron shuttles. These compounds can easily accept electrons (i.e., be reduced) or lose them (i.e., be oxidized). They play an essential role in energy production because cellular respiration is contingent on the flow of electrons.
Over the many stages of cellular respiration, glucose breaks down into carbon dioxide and water. Electron carriers pick up electrons lost by glucose in these reactions, temporarily storing and releasing them into the electron...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

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Related Experiment Video

Updated: Jun 14, 2026

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity
11:30

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

Published on: March 6, 2017

Charge carrier dynamics in thiol capped CdTe quantum dots.

Sreejith Kaniyankandy1, Sachin Rawalekar, Sandeep Verma

  • 1Radiation and Photochemistry Division, Bhabha Atomic Research Center, Mumbai-400 085, India. sreeji@barc.gov.in

Physical Chemistry Chemical Physics : PCCP
|April 10, 2010
PubMed
Summary
This summary is machine-generated.

Ultrafast charge carrier relaxation in cadmium telluride quantum dots (QDs) was studied. Surface defects significantly influence carrier cooling, with distinct electron and hole cooling and trapping times observed.

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Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method
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Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Published on: April 18, 2019

Compact Quantum Dots for Single-molecule Imaging
17:14

Compact Quantum Dots for Single-molecule Imaging

Published on: October 9, 2012

Related Experiment Videos

Last Updated: Jun 14, 2026

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity
11:30

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

Published on: March 6, 2017

Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method
07:38

Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method

Published on: April 18, 2019

Compact Quantum Dots for Single-molecule Imaging
17:14

Compact Quantum Dots for Single-molecule Imaging

Published on: October 9, 2012

Area of Science:

  • Materials Science
  • Physical Chemistry
  • Nanotechnology

Background:

  • Quantum dots (QDs) exhibit unique optical and electronic properties due to quantum confinement.
  • Understanding charge carrier dynamics is crucial for QD applications in optoelectronics and photovoltaics.
  • Surface chemistry, such as capping ligands, can significantly impact QD performance.

Purpose of the Study:

  • To investigate the ultrafast charge carrier relaxation dynamics in mercaptopropionic acid capped CdTe quantum dots.
  • To determine the cooling and trapping times of electrons and holes in different excitonic states.
  • To elucidate the role of surface defect states in carrier relaxation processes.

Main Methods:

  • Femtosecond transient absorption spectroscopy was employed to monitor carrier dynamics.
  • Excitation was performed using 400 nm laser light, with transients observed in the visible to near-infrared region.
  • Quenching studies were utilized to differentiate and quantify electron and hole cooling and trapping.

Main Results:

  • Cooling times for the second and first excitonic states were measured at 150 fs and 500 fs, respectively, showing non-linear size dependence.
  • Electron and hole cooling times for the first excitonic state were determined to be 700 fs and 150 fs using quenchers.
  • Electron and hole trapping times were found to be 700 fs and 1 picosecond (ps) in CdTe QDs.

Conclusions:

  • Surface defect states play a critical role in the cooling dynamics of charge carriers within CdTe QDs.
  • Individual electron and hole relaxation pathways differ significantly, impacting overall carrier recombination.
  • The findings provide insights into the fundamental charge carrier behavior in QDs, essential for designing advanced nanomaterials.