Compound semiconductors

What is the problem called in which LED external quantum efficiency is high for blue (InGaN) and red (AlGaInP) but low in the green-to-yellow range between them?

  1. ARed-out
  2. BBlue shift
  3. CGreen gap
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Answer: C. Green gap

Producing green from InGaN requires a high In fraction, which lowers efficiency through degraded crystal quality and strong polarization fields. In AlGaInP, efficiency falls as the wavelength shortens because of band-structure issues. High-efficiency LEDs are therefore hard to obtain in the green-to-yellow range, a problem known as the green gap.

  • A. There is no problem by that name.
  • B. Blue shift is a shift of the emission wavelength toward shorter values.
  • C. Correct. It is the efficiency dip in the green-to-yellow range.
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More Compound semiconductors questions

  1. Which correctly describes a "type I" band alignment at a heterojunction?
  2. Why does Mg-doped GaN grown by MOCVD remain highly resistive rather than p-type right after growth, and what is the countermeasure?
  3. What is the phenomenon called in which the efficiency of an InGaN LED actually decreases as the current is increased?
  4. What does LED stand for?
  5. What type of band structure does gallium arsenide (GaAs) have?