GATE 2022 PH – Question 28
For a bipolar junction transistor, which of the following statements are true?
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: (A) Doping concentration of emitter region is more than that in collector and base region; (C) The current gain β depends on temperature; (D) Collector current is less than the emitter current
Explanation
Check each statement about a bipolar junction transistor (BJT).
- **A. The emitter is more heavily doped than the collector and the base.** True. The emitter is heavily doped so that it can inject many carriers into the base. ✓
- **B. Only electrons take part in conduction.** False. Both electrons and holes take part (a BJT is *bipolar*).
- **C. The current gain $\beta$ depends on temperature.** True: the carrier lifetimes, mobilities and the base width (Early effect) change with temperature. ✓
- **D. The collector current is less than the emitter current.** True: $I_E=I_C+I_B$, so $I_C<I_E$. ✓
Answer **A, C and D**.