Atom to be stable we need to have 8 valency electrons. So that if we have nucleus as 4 then we can get 4 on valency electrons.

Characteristics of Intrinsic Semiconductors

Intrinsic semiconductors are materials that have a valence shell of 4 electrons. These materials are pure and have no impurities or doping elements added to them. Intrinsic semiconductors include materials like silicon (Si) and germanium (Ge).

Valence Shell

The valence shell of an atom refers to the outermost shell that contains electrons. These electrons are involved in forming chemical bonds with other atoms. In the case of intrinsic semiconductors, the valence shell of each atom contains 4 electrons.

Explanation of the Correct Answer (Option B)

The correct answer to the question is option B, which states that intrinsic semiconductor materials are characterized by a valence shell of 4 electrons. This is the case for materials like silicon and germanium, which are widely used in the field of electrical engineering.

Significance of Valence Shell in Semiconductors

The valence shell of an atom plays a crucial role in determining the electrical properties of a semiconductor material. Intrinsic semiconductors have a valence shell of 4 electrons, which means that each atom can form covalent bonds with four neighboring atoms.

Covalent Bonds in Intrinsic Semiconductors

In an intrinsic semiconductor material like silicon or germanium, each atom forms four covalent bonds with its neighboring atoms. These covalent bonds result in a stable crystal lattice structure. Each covalent bond involves the sharing of one electron between two adjacent atoms, creating a strong bond.

Effect on Electrical Conductivity

The four covalent bonds in intrinsic semiconductors make them poor conductors of electricity at room temperature. This is because all the valence electrons are involved in covalent bonding and are not free to move. As a result, there are no available charge carriers to conduct electricity.

Temperature and Electrical Conductivity

However, at higher temperatures, some of the covalent bonds can break, releasing electrons and creating holes. These free electrons and holes can contribute to the electrical conductivity of the material. As the temperature increases, more covalent bonds break, leading to an increase in the number of charge carriers and an increase in conductivity.

Doping to Modify Electrical Properties

To enhance the electrical conductivity and alter the electrical properties of intrinsic semiconductors, impurities can be added through a process called doping. This involves introducing specific atoms with either more or fewer valence electrons than the host material. Doping can create extrinsic semiconductors with either excess electrons (n-type) or excess holes (p-type), which significantly improve the conductivity and allow for the design of various electronic devices.

Therefore, the correct answer to the question is option B, which states that intrinsic semiconductor materials are characterized by a valence shell of 4 electrons.

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