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Related Concept Videos

Semiconductors01:22

Semiconductors

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There is variation in the electrical conductivity of materials - metals, semiconductors, and insulators that are showcased with the help of the energy band diagrams.
Metals such as copper (Cu), zinc (Zn), or lead (Pb) have low resistivity and feature conduction bands that are either not fully occupied or overlap with the valence band, making a bandgap non-existent. This allows electrons in the highest energy levels of the valence band to easily transition to the conduction band upon gaining...
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Types of Semiconductors01:20

Types of Semiconductors

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Intrinsic semiconductors are highly pure materials with no impurities. At absolute zero, these semiconductors behave as perfect insulators because all the valence electrons are bound, and the conduction band is empty, disallowing electrical conduction. The Fermi level is a concept used to describe the probability of occupancy of energy levels by electrons at thermal equilibrium. In intrinsic semiconductors, the Fermi level is positioned at the midpoint of the energy gap at absolute zero. When...
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Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

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The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
932
Biasing of Metal-Semiconductor Junctions01:27

Biasing of Metal-Semiconductor Junctions

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Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
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Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

8.8K
Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
8.8K
Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

10.1K
Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
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Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope
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Defect Dynamics in Self-Catalyzed III-V Semiconductor Nanowires.

James A Gott1, Richard Beanland1, H Aruni Fonseka1

  • 1Department of Physics , University of Warwick , Coventry CV4 7AL , United Kingdom.

Nano Letters
|June 13, 2019
PubMed
Summary

Line defects in III-V semiconductor nanowires are analyzed. Annealing experiments show most defects move and are removed, but some remain stable, indicating potential for improved material quality.

Keywords:
DefectsSTEMTEMin situnanowires

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Area of Science:

  • Materials Science
  • Semiconductor Physics
  • Nanotechnology

Background:

  • Self-catalyzed III-V semiconductor nanowires (NWs) can develop line defects during droplet consumption.
  • These defects often associate with twin boundaries and possess a null Burgers vector, implying no long-range strain field.

Purpose of the Study:

  • To analyze the stability and behavior of line defects in GaAsP nanowires (NWs).
  • To investigate defect movement mechanisms and their dependence on environmental factors.
  • To determine the effectiveness of annealing in defect removal and assess thermodynamic stability.

Main Methods:

  • In situ aberration-corrected scanning transmission electron microscopy (STEM) was employed.
  • Short annealing cycles were applied to observe defect dynamics.
  • Forces acting on defects were considered to analyze their stability.

Main Results:

  • Defect movement was observed consistent with thermally activated dislocation glide mechanisms (single- or double-kink), with velocities below 1 nm s-1.
  • Defect motion is influenced by size, position, and local environment, with an activation energy limit of approximately 2 eV.
  • Post-growth annealing above 640 °C for seconds removed over 70% of defects.

Conclusions:

  • In situ annealing during growth at lower temperatures could significantly enhance material quality.
  • A fraction of defects are thermodynamically stable and do not move, persisting even after annealing.