Bipolar Junction Transistor (BJT) Construction

• It is a three layer semiconductor device, comprising of either two n- and one p-type layers of material or two p- and one n-type layers.
• As three layers are included in this device, thus it consist of three terminals. These terminals are   called as:-

1.     Emitter.

2.   Base.

3.   Collector.

• Emitter layer is greatly doped.
• Base layer is very less doped.
• Collector is very less doped.
• The base layer is extremely thin in comparison to other two, generally in the range of 150:1.
• The designated terminology for three terminals is given as under:-

    Emitter:        This layer gives electrons.

    Base:            It assists minority carriers to transfer quickly from emitter to collector. Electric field is developed in base through non-uniform doping, thus minority carriers are accelerated from emitter to collector.

    Collector:    This layer gathers the emitted electrons.

• Two essential types of BJTs
• These types are in equation to constructional arrangement of layers.
• The arrangement exhibited in the figure is known as NPN Transistor.