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P-N junction01:11

P-N junction

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A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
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Carrier Generation and Recombination01:22

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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.
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Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Imagine a bucket of water. It contains many molecules, of the order of 1026 molecules. Thus, although it contains discrete elements (molecules) at the microscopic level, macroscopically, it can be considered continuous. Small volume elements of water, infinitesimal compared to the bulk of the bucket's volume, still contain many molecules. Under this framework, quantized matter is approximated as continuous for practical purposes.
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The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
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A permanent electric dipole orients itself along an external electric field. This rotation can be quantified by defining the potential energy because the external torque does work in rotating it. Then, the potential energy is minimum at the parallel configuration and maximum at the antiparallel configuration. While the former is a stable equilibrium, the latter is an unstable equilibrium.
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Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity
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Highly Nonlinear Biexcitonic Photocurrent from Ultrafast Interlayer Charge Transfer.

Sarthak Das1, Garima Gupta1, Suman Chatterjee1

  • 1Department of Electrical Communication Engineering, Indian Institute of Science, Bangalore 560012, India.

ACS Nano
|May 23, 2022
PubMed
Summary

Researchers developed a self-powered photodetector using monolayer tungsten disulfide (WS2) and graphene. This device utilizes charged biexcitons for highly nonlinear photocurrent generation, enabling ultrafast photoresponse for optoelectronics.

Keywords:
Charged biexcitonPhotocurrent spectroscopyPhotoluminescence excitation spectroscopySuperlinear photocurrentultrafast charge transfervan der Waals heterojunction

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Optoelectronics

Background:

  • Monolayer semiconductors exhibit strong Coulomb interactions, enabling optically active many-body states like charged biexcitons.
  • Charged biexcitons show strong nonlinear light absorption, suggesting potential for nonlinear photodetection, an underexplored area.

Purpose of the Study:

  • To investigate nonlinear photocurrent generation in a 1L-WS2 heterostructure using charged biexcitons.
  • To explore the potential of many-body effects in monolayers for self-powered optoelectronic applications.

Main Methods:

  • Fabrication of an asymmetrically designed few-layer graphene encapsulated 1L-WS2 heterostructure.
  • Utilizing a built-in vertical electric field for self-powered photodetection.
  • Employing time-resolved and photoluminescence excitation spectroscopy to analyze photocurrent and biexciton dynamics.

Main Results:

  • Observed a large, highly nonlinear photocurrent in self-powered mode due to strong absorption by charged biexcitons.
  • Demonstrated ultrafast charge transfer (sub-5 ps) from WS2 to graphene.
  • Identified two biexcitonic peaks originating from bright-dark and bright-bright exciton-trion combinations.

Conclusions:

  • The study exemplifies the promise of manipulating many-body effects in monolayers for optoelectronics.
  • Innate nonlinearity and ultrafast response highlight the potential of WS2-graphene heterostructures for advanced photodetection.