# Static current gain of BJT?

• rclakmal
In summary, for a BJT, thin base means less area for recombination, and less doping means less recombination.

#### rclakmal

static current gain of BJT?

to increase the static current gain of a BJT what should i do ?////////

1.base is made thin and heavily doped
2. collector is made thick and heavily doped
3.base is made thin and lightly doped
4.emitter is made thin and heavily doped

its an MCq question so i don't have any kind of pre works to show u hope that someone will help me with an answer with a valid reason.

making thin and lightly doped base,
the recombination will be much less.
so,
amount of current coming from collector to emitter (or reverse),will be more and gain will be more.

*the main problem for currebt gain is recombination.
thin base means less area for recombination,
and
less doping also means so.

**for MCQ question,
this is the most likely factor,than others.

Actually, in today's bipolar transistors, the base is so thin that there is very little recombination. So the current gain is almost completely determined by the emitter efficiency. That is (for an NPN transistor) how much of the emitter current is composed of electrons injected from the emitter into the base , and how much is composed of holes injected from the base into the emitter. The higher the ratio of these two currents, the higher the gain. This ratio is determined by the ratio of emitter doping to base doping, so a heavily doped emitter and lightly doped base increases the current gain.

1 person

phyzguy said:
Actually, in today's bipolar transistors, the base is so thin that there is very little recombination. So the current gain is almost completely determined by the emitter efficiency. That is (for an NPN transistor) how much of the emitter current is composed of electrons injected from the emitter into the base , and how much is composed of holes injected from the base into the emitter. The higher the ratio of these two currents, the higher the gain. This ratio is determined by the ratio of emitter doping to base doping, so a heavily doped emitter and lightly doped base increases the current gain.

this answer is really more practical and right than mine.