Compound semiconductors

What is the gate structure of the MESFET, long used as a high-frequency GaAs transistor?

  1. AA MOS structure with the gate on a thick oxide
  2. BA structure using a PN junction as the gate
  3. CA structure using a Schottky junction, with the metal directly contacting the semiconductor, as the gate
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Answer: C. A structure using a Schottky junction, with the metal directly contacting the semiconductor, as the gate

A MESFET (metal-semiconductor FET) uses a Schottky junction formed by the gate metal directly contacting the semiconductor as its gate. Because good insulating films are hard to form on GaAs, this structure is used instead of MOS, and it has been widely employed in high-frequency circuits such as those in mobile phones.

  • A. It is not a MOS structure but one with the metal in direct contact.
  • B. Using a PN junction as the gate is a junction FET (JFET).
  • C. Correct. It uses a Schottky junction as the gate.
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  2. In LEDs with an InGaN emitting layer, how does the emission color change when the indium (In) fraction is increased?
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  4. Which material, whose band gap can be tuned by composition, has been used for high-performance mid- to long-wave infrared detectors?
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