Substrate
Substrate is known as supporting material. It provide mechanical support, electrical isolation, and thermal dissipation. Also it has high melting point (1400°C). So upon which or within which the elements of semiconductor device are fabricated or attached.
Live example: soil is the substrate for plants. Soil act as a supporting material for plant.
Intrinsic Semiconductor
Semiconductor that are pure, in other words free from impurities are called as Intrinsic Semiconductor. That is, number of existed electrons are equal to number of holes (e = p).
Extrinsic Semiconductor
If the impurities are doped to the pure semiconductor, then it becomes Extrinsic Semiconductor.
Doping
Doping is the process of adding impurities to the intrinsic semiconductors to change their properties. Normally Trivalent and Pentavalent elements are used to dope Silicon.
If the intrinsic semiconductor is dopped with trivalent (3 electrons) impurities, then it becomes p-type semiconductor.
Trivalent materials: Boron, Gallium, Aluminium (Acceptor Impurities)
If the intrinsic semiconductor is dopped with pentavalent (5 electrons) impurities, then it becomes n-type semiconductor.
Pentavalent materials: Phosphorus, Nitrogen, Arsenic (Donor Impurities)
Diffusion
Diffusion is the net movement of anything (electron, hole, atom, ions) generally from a region of higher concentration to region of lower concentration.
n-Well
n-Well is created in p-type substrate by digging well and putting n-type material in that well.
In p-type substrate, we can make nMOS.
In n-type substrate, we can make pMOS.
But in CMOS technology, we need both nMOS and pMOS transistors to build a circuit. Both nMOS and pMOS must be fabricated on the same silicon substrate (wafer).
The wafer are mostly p-type. So, we can only make nMOS transistors in those wafers. To fabricate a pMOS transistors, we dope a selected regions of the wafer to be n-type. By digging well and fill that well by n-type material is called as n-well.
N-channel MOSFET (NMOS): In an NMOS transistor, the semiconductor channel is made of n-type material (electron-rich). The gate voltage controls the flow of electrons from the source to the drain. When a positive voltage is applied to the gate with respect to the source, it creates an electric field that attracts electrons, forming a conductive channel between the source and drain, allowing current to flow.
P-channel MOSFET (PMOS): In a PMOS transistor, the semiconductor channel is made of p-type material (hole-rich). The gate voltage controls the flow of holes from the source to the drain. When a negative voltage is applied to the gate with respect to the source, it creates an electric field that attracts holes, forming a conductive channel between the source and drain, allowing current to flow.
