Explain the construction of n channel and p channel FET. Differentiate FET with BJT.

Construction of n-channel and p-channel FET

1. n-channel FET

Substrate: An n-type semiconductor substrate forms the base of the FET. It is lightly doped with donor atoms, creating a majority of free electrons and a minority of holes.

Source and Drain: Two heavily doped n-type regions, known as the source and drain, are created at two opposite ends of the substrate. These regions have a high concentration of donor atoms, leading to a large number of free electrons.

Gate: A thin layer of insulating material, such as silicon dioxide (SiO2), is deposited over the substrate. This layer acts as a barrier between the gate and the channel.

Gate Electrode: A metal electrode, typically made of aluminum or polysilicon, is placed on top of the insulating layer. This electrode serves as the gate terminal of the FET.

2. p-channel FET

Substrate: A p-type semiconductor substrate forms the base of the FET. It is lightly doped with acceptor atoms, creating a majority of free holes and a minority of electrons.

Source and Drain: Two heavily doped p-type regions, known as the source and drain, are created at two opposite ends of the substrate. These regions have a high concentration of acceptor atoms, leading to a large number of free holes.

Gate: A thin layer of insulating material, such as silicon dioxide (SiO2), is deposited over the substrate. This layer acts as a barrier between the gate and the channel.

Gate Electrode: A metal electrode, typically made of aluminum or polysilicon, is placed on top of the insulating layer. This electrode serves as the gate terminal of the FET.

Differentiation between FET and BJT

Feature	FET	BJT
Charge Carriers in Channel	Electrons (n-channel) or Holes (p-channel)	Both Electrons and Holes
Majority Carriers	Majority Carriers are Used	Both Majority and Minority Carriers are Used
Gate Terminal	Yes, Controls the Conductivity of the Channel	No Gate Terminal
Input Resistance	Very High (Gate-Source/Drain Capacitance)	Low (Base-Emitter Junction)
Output Resistance	Low (Channel Resistance)	High (Collector-Emitter Resistance)
Current Gain	No Current Gain (Voltage-Controlled Device)	High Current Gain (Current-Controlled Device)
Switching Speed	Faster (Less Charge Storage)	Slower (More Charge Storage)
Power Handling Capability	Lower (Lower Current and Voltage Ratings)	Higher (Higher Current and Voltage Ratings)
Applications	Amplifiers, Switches, Logic Circuits	Amplifiers, Power Electronics, High-Speed Circuits