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Photoemission spectroscopy reveals that higher indium content in p-InGaN/GaN photocathodes significantly reduces quantum yield at lower temperatures. This is due to electron localization caused by alloy disorder, impacting photoelectron transport.

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Area of Science:

  • Solid State Physics
  • Materials Science
  • Quantum Mechanics

Background:

  • Negative electron affinity photocathodes are crucial for electron emission applications.
  • Gallium Nitride (GaN) based materials are promising for optoelectronic devices.
  • Indium Gallium Nitride (InGaN) alloys offer tunable band gaps.

Purpose of the Study:

  • Investigate the temperature-dependent photoemission properties of p-InGaN/GaN photocathodes.
  • Understand the role of indium content and alloy disorder on photoelectron transport.
  • Determine the mechanism behind the observed drop in quantum yield at low temperatures.

Main Methods:

  • Near-band-gap photoemission spectroscopy.
  • Experiments conducted on p-GaN and p-InGaN/GaN photocathodes activated to negative electron affinity.
  • Variable temperature measurements from room temperature down to cryogenic levels.

Main Results:

  • Photoemission quantum yield of InGaN with >5% indium dropped by over an order of magnitude as temperature decreased.
  • Quantum yield remained constant for InGaN with lower indium content.
  • A characteristic peak in the photoemission spectrum, corresponding to photoelectrons relaxed at the InGaN conduction band edge, disappeared at low temperatures.

Conclusions:

  • The observed drop in quantum yield is attributed to the freezing of photoelectron transport in p-InGaN.
  • Electron localization within the fluctuating potential induced by alloy disorder is the primary cause.
  • This localization effect hinders efficient electron emission at low temperatures for high-indium content InGaN.