Compound semiconductors

When a strong field is applied to GaAs, electrons transfer to another valley with lower mobility, and negative differential resistance appears in which current decreases as the field rises. Which oscillator device uses this?

  1. AGunn diode
  2. BZener diode
  3. CPhotodiode
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Answer: A. Gunn diode

In GaAs, electrons accelerated by a strong field transfer to an upper valley with larger effective mass and lower mobility, so above a certain field the drift velocity decreases (the transferred-electron effect). Using this negative differential resistance, a Gunn diode oscillates at microwave frequencies with only a DC bias.

  • A. Correct. It is a microwave oscillator using the transferred-electron effect.
  • B. A Zener diode is a voltage regulator using reverse breakdown.
  • C. A photodiode detects light.
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