Question

By adding impurity in intrinsic semiconductor \(\mathrm{P}\) type semiconductor is made. charge of these P type semiconductor is (A) trivalent, neutral (B) pentavalent, neutral (C) pentavalent, positive (D) trivalent, negative

Short answer

The correct answer is (D) trivalent, negative. This is because adding a trivalent impurity atom, such as boron, aluminum, or gallium, to an intrinsic semiconductor creates a P-type semiconductor with an excess concentration of holes, making the trivalent impurity atom negatively charged.

Step-by-step solution

Understanding Intrinsic Semiconductors and P-type Semiconductors

Intrinsic semiconductors are pure semiconductors, typically silicon or germanium, that have an equal number of holes and electrons - making them electrically neutral. P-type semiconductors are created by adding impurities to the intrinsic semiconductor, which increases the concentration of holes in the material.

Identify the Impurity Added for P-type Semiconductor

To create a P-type semiconductor, trivalent impurity atoms such as boron, aluminum, or gallium are added to the intrinsic semiconductor. These trivalent elements have one less electron in their outermost shell compared to the semiconductor, which results in the creation of additional holes in the material.

Determine the Charge after Adding the Impurity

When trivalent impurity atoms like boron, aluminum, or gallium are added to the intrinsic semiconductor, they form covalent bonds with the semiconductor atoms and accept electrons from the semiconductor's valence band. As a result, the trivalent impurity atom becomes negatively charged, and the P-type semiconductor becomes relatively more positive due to the excess concentration of holes.

Choose the Correct Option

From the above analysis, we know that the P-type semiconductor is created by adding a trivalent impurity atom, which becomes negatively charged. Therefore, the correct option is: (D) trivalent, negative

Key concepts

Intrinsic Semiconductor

An intrinsic semiconductor is a pure form of semiconductor material that consists mainly of silicon or germanium. It is characterized by having an equal number of free electrons and holes. In this natural state, both carriers balance each other out, resulting in an electrically neutral material. This balance is crucial as it allows intrinsic semiconductors to conduct electricity, although not very effectively at room temperature.
To enhance their conductivity, intrinsic semiconductors are often modified by adding specific impurities, which leads to the formation of extrinsic semiconductors, such as P-type and N-type semiconductors.

Trivalent Impurities

Trivalent impurities include elements like boron, aluminum, and gallium, which have three electrons available for bonding in their outer shell. When these impurities are introduced into an intrinsic semiconductor like silicon or germanium, they replace some of the semiconductor's atoms and form three strong covalent bonds with the surrounding semiconductor atoms.
This process leaves one hole, or absent electron, because these impurities lack the fourth electron needed for complete covalent bonding within the crystal lattice. This addition increases the number of holes in the material, facilitating the creation of P-type semiconductors and enhancing the material's ability to conduct positive charge.

Charge of Semiconductors

The charge of a semiconductor is a critical property determining its behavior in electronic devices. In an intrinsic semiconductor, the overall charge is neutral due to an equal number of electrons and holes. However, when trivalent impurities are added to form a P-type semiconductor, the impurity atoms can become negatively charged because they take on an extra electron to complete their bonding.
The material as a whole becomes positively "doped" due to the excess of holes, even though it remains electrically neutral overall. This is because the increased number of holes, acting as positive charge carriers, dominate the flow of electricity.

Electrons and Holes in Semiconductors

In semiconductor physics, electrons and holes play a pivotal role. Electrons are negatively charged particles, while holes are considered as positive charge carriers, essentially vacant positions left by missing electrons. In intrinsic semiconductors, electrons get excited from the valence band to the conduction band, creating pairs of free electrons and holes.
In the case of P-type semiconductors, the introduction of trivalent impurities increases the number of available holes. This implies that when an electric field is applied, these holes move towards the negative terminal, creating the appearance of positive charge flow. Understanding this movement is crucial for designing semiconductor devices that rely on the controlled flow of charge, such as transistors and diodes.