Analog Electronics
Optocouplers combine

 IGBTs and MOSFETs.
  Infrared light emitting diode and a silicon photo transistor.
 Power transistor and silicon transistor.
 SITs and BJTs.

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Analog Electronics
For transistor action

  the base region must be very thin and lightly doped.
  all of these.
  the emitter should be heavily doped.
  Je must be forward biased and Jc should be reverse biased.

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