Bipolar transistors

What is the main reason for making the base of a bipolar transistor thin?

  1. ATo raise the collector breakdown voltage
  2. BTo lower the base resistance
  3. CTo reduce recombination in the base and increase the current gain
Show answer and explanation

Answer: C. To reduce recombination in the base and increase the current gain

Some of the carriers injected from the emitter into the base recombine and are lost while crossing the base. A thinner base shortens the transit time and reduces recombination, so more carriers reach the collector and the current gain increases. A thinner base, however, raises the base resistance and makes punch-through more likely, which is a disadvantage for breakdown voltage.

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More Bipolar transistors questions

  1. When a bipolar transistor is used as a switch, which operating region corresponds to the on state?
  2. How does the phase of the output voltage of a common-emitter amplifier compare with the input voltage?
  3. What is the main reason for making the emitter of an NPN transistor more heavily doped than the base?
  4. What is the approximate common-emitter current gain β of a bipolar transistor whose common-base current gain α is 0.99?
  5. Which correctly describes the Early effect in a bipolar transistor?