Differences between BJTs and FETs
The difference between a BJT, or bipolar junction transistor, and an FET, or field effect transistor, mainly lies in its control and polarity. BJT is bipolar and FET is unipolar. A BJT is primarily controlled by current, while an FET is mainly controlled by voltage.
A BJT relies on two different charge carriers, hole and electron for its conduction level, while an FET relies on one charge carrier, either hole or electron for its conduction level. An n-channel FET has electron as its charge carrier. Hole is the charge carrier for a p-channel FET. BJTs can be NPN or PNP transistors.
Other differences between a BJT and an FET are in terms of temperature stability and size. Normally, an FET is smaller with a more stable temperature than a BJT.
Finally, bipolar transistors are superior in the fact that they provide greater amplification, even though FETs are better in that they cause less loading, are cheaper, and easier to manufacture.