Boron

Arsenic

Antimony

Phosphorous

Base ground, emitter and collector positive

Base negative, emitter positive and collector negative

Base positive, emitter negative and collector positive

Base positive, emitter negative and collector negative

To reduce the distortion

To increase the amplification factor

To increase the output voltage gain

To increase the output current gain

As rectifier

For triggering

As an oscillator

For amplification

FET

UJT

DIAC

TRIAC