Test: BJT Construction & Operation - Electronics and Communication Engineering (ECE) MCQ

A BJT is a device with a layer of semiconductor sandwitched between 2 unlike types of semiconductors and hence, PPN is not a valid type of a BJT.

In a BJT, the thickness of the middle layer or the base is thin as compared to the collector and emitter.

In a BJT, emitter is heavily doped whereas base and collector are lightly doped.

 As the base is lightly doped, the number of free charge carriers are less and hence the resistance is high and as the emitter is the most highly doped, its resistance is low.

On application of a forward bias voltage across E-B junction, the width of the depletion region decreases.

 In a BJT, one junction is forward biased and the other is reverse biased depending upon the type of the transistor.

As the base current is quite lower as compared to the collector and emitter current, it is usually in the order of microamperes.

The collector current I _C in a BJT is made up of two components – one due to majority carriers and the other due to minority carriers. The component of I_C due to minority carriers i.e I_CO is temparature sensitive.

Leakage current in a BJT is the name given to I_CO, which is due to the flow of minority carriers.

On applying KCL to the BJT, we get I_C + I_B = I_E.