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Excitonic Diffusion in InGaN/GaN Core-Shell Nanowires.

M Shahmohammadi1, J-D Ganière1, H Zhang2

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Nano Letters
|December 18, 2015
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Carrier diffusion in graded InGaN/GaN quantum wells is thermally activated and isotropic, not following the indium gradient. This confirms nanowires

Keywords:
CathodoluminescenceLEDcore−shell nanowireexciton hoppinglocalization

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Area of Science:

  • Materials Science
  • Condensed Matter Physics
  • Semiconductor Physics

Background:

  • Indium gallium nitride (InGaN) quantum wells are crucial for light-emitting diodes (LEDs), but their efficiency is limited by carrier behavior.
  • Understanding carrier dynamics in graded InGaN/GaN quantum wells is essential for optimizing LED performance, particularly in nanowire structures.

Purpose of the Study:

  • To directly observe and analyze the diffusion of carriers within graded InGaN/GaN quantum wells in a nanowire structure.
  • To investigate the temperature dependence and nature of carrier diffusion, and its impact on device performance.

Main Methods:

  • Utilized nanoscale probing of local dynamics at various temperatures (4 K to 250 K).
  • Analyzed cathodoluminescence lifetime measurements at different temperatures.
  • Employed theoretical interpretation based on hopping processes and alloy fluctuation effects.

Main Results:

  • Observed that carrier diffusion in graded InGaN/GaN quantum wells is a thermally activated process.
  • Determined that carrier motion is isotropic and does not follow the indium composition gradient.
  • Identified random alloy fluctuations as the primary factor preventing directional drift and carrier accumulation.

Conclusions:

  • Carrier diffusion occurs via a hopping mechanism between localized states, influenced by alloy disorder.
  • The isotropic nature of carrier motion and lack of accumulation confirm the suitability of core-shell nanowires for lighting applications.
  • Homogeneous carrier distribution and short lifetimes in m-plane quantum wells mitigate efficiency issues at high carrier densities.