Explain the construction of n channel and p channel FET.

N-Channel Field Effect Transistor (FET)

1. Starting Material: We start with a lightly doped n-type silicon wafer. This wafer serves as the FET's substrate.

2. Source and Drain Formation:

• Photolithography and etching are used to create two heavily doped n-type regions (the source and drain) at the two ends of the substrate.
• These regions are typically formed by ion implantation or diffusion of donor impurities (typically arsenic or phosphorus) into the substrate.

1. Gate Electrode:

• A thin layer of silicon dioxide (SiO2) is grown on the substrate's surface using thermal oxidation. This oxide acts as the gate insulator.
• A conducting material, such as polysilicon, metal (e.g., aluminum), or a metal silicide, is deposited on the oxide.
• This material is patterned and etched to form the gate electrode, which controls the channel conduction.

1. Channel Formation:

• Between the source and drain, ion implantation or diffusion of acceptor impurities (typically boron) is performed to create a lightly doped p-type region called the channel.
• This p-type region is critical for controlling the flow of current through the FET.

1. Ohmic Contacts:

• Ohmic contacts are formed between the source, drain, and gate terminals and the external circuit.
• These contacts allow for efficient flow of current between the FET and the external circuit.

P-Channel Field Effect Transistor (FET)

1. Starting Material: We start with a lightly doped p-type silicon wafer. This wafer serves as the FET's substrate.

2. Source and Drain Formation:

• Photolithography and etching are used to create two heavily doped p-type regions (the source and drain) at the two ends of the substrate.
• These regions are typically formed by ion implantation or diffusion of acceptor impurities (typically boron) into the substrate.

1. Gate Electrode:

• A thin layer of silicon dioxide (SiO2) is grown on the substrate's surface using thermal oxidation. This oxide acts as the gate insulator.
• A conducting material, such as polysilicon, metal (e.g., aluminum), or a metal silicide, is deposited on the oxide.
• This material is patterned and etched to form the gate electrode, which controls the channel conduction.

1. Channel Formation:

• Between the source and drain, ion implantation or diffusion of donor impurities (typically arsenic or phosphorus) is performed to create a lightly doped n-type region called the channel.
• This n-type region is critical for controlling the flow of current through the FET.

1. Ohmic Contacts:

• Ohmic contacts are formed between the source, drain, and gate terminals and the external circuit.
• These contacts allow for efficient flow of current between the FET and the external circuit.

In summary, the construction of n-channel and p-channel FETs involves the creation of a lightly doped channel region, heavily doped source and drain regions, a gate electrode, and ohmic contacts. The difference between the two types of FETs lies in the doping types of the channel region and the source and drain regions, which determine the majority carrier type and the direction of current flow.