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Assertion (A): A high electron mobility transistor is based upon modulation-doped (GaAs - AlGaAs) single heterojunction structure. Reason (R): HEMT shows a very high noise figure and very low gain at very high microwave frequencies up to 70 GHz.

Assertion (A): A high electron mobility transistor is based upon modulation-doped (GaAs - AlGaAs) single heterojunction structure. Reason (R): HEMT shows a very high noise figure and very low gain at very high microwave frequencies up to 70 GHz. Correct Answer (A) is true, but (R) is false

  • The High Electron Mobility Transistor is a form of Field Effect Transistor (FET) that uses a junction between two materials with different bandgaps (i.e. a heterojunction) as the channel.
  • The most common material used is aluminum gallium arsenide (AlGaAS) and gallium arsenide (GaAs) (Assertion is Correct)
  • Gallium Arsenide (GaAs) is generally used because it provides high-level basic electron mobility.
  • The basic structure of HEMT is shown below.

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Advantages:

  • High Gain: HEMT’S have high gain at microwave frequencies because the charge carriers are almost exclusively the majority carriers. Minority carriers are not significantly involved.
  • Low Noise: HEMT’S provide very low noise operation because the current variation in the devices is low. (Reason is False)

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