Question

We can not make \(\mathrm{p}-\mathrm{n}\) junction diode by making \(\mathrm{P}\) type semi-conductor join with N-type semi-conductor, because (A) Inter-atomic spacing becomes less than \(1 \mathrm{~A}^{\circ}\) (B) P-type will repel N-type (C) There will be discontinuity for the flowing charge carriers (D) semi-conducting properties will be lost

Short answer

Analysis of each option reveals none of them prevent the formation of a p-n junction diode by joining a P-type and an N-type semiconductor. Option A is invalid since the inter-atomic spacing depends on the crystal lattice of the semiconductor, not on the junction. Option B is incorrect as both P-type and N-type semiconductors are made from the same base material and do not repel each other. Option C does not hold as the continuous flow of charge carriers is enabled by the applied voltage across the junction, despite recombination at the junction. Option D is untrue as the semiconducting properties of each semiconductor are preserved when joined. Thus, we can construct a p-n junction by connecting a P-type and an N-type semiconductor.

Step-by-step solution

Understanding P-type and N-type Semiconductors

A P-type semiconductor has an abundance of positive charge carriers (holes) while an N-type semiconductor has an abundance of negative charge carriers (electrons). When a P-type semiconductor is joined with an N-type semiconductor, a p-n junction is formed, which is the basis of many semiconductor devices like diodes, transistors, etc. Hence, the statement "We cannot make p-n junction diode by making P-type semiconductor join with N-type semiconductor" is incorrect. However, we will examine the given options and explain why they are not valid reasons to prevent the formation of a p-n junction diode.

Option A: Inter-atomic spacing becomes less than 1 Å

Inter-atomic spacing is a property of the crystal lattice of the semiconductor material and is not affected by joining P-type and N-type semiconductors. So, this option is not a valid reason to prevent the formation of a p-n junction diode.

Option B: P-type will repel N-type

Both P-type and N-type semiconductors are made of the same base material (silicon or germanium), and there is no reason for them to repel each other when they are joined. So, this option is not a valid reason to prevent the formation of a p-n junction diode.

Option C: There will be discontinuity for the flowing charge carriers

When a P-type semiconductor is joined with an N-type semiconductor, a p-n junction is formed. At this junction, electrons and holes recombine, resulting in a depletion region with no free charge carriers. However, the flow of charge carriers can still happen through the applied voltage across the junction. So, this option is not a valid reason to prevent the formation of a p-n junction diode.

Option D: Semi-conducting properties will be lost

When a P-type semiconductor is joined with an N-type semiconductor, their individual properties do not change. The P-N junction diode formed by joining them can still make use of their semi-conducting properties for its working as a rectifier or an electronic switch. So, this option is not a valid reason to prevent the formation of a p-n junction diode. To summarize, all the given options (A, B, C, and D) are not valid reasons to prevent the formation of a p-n junction diode when a P-type semiconductor is joined with an N-type semiconductor.

Key concepts

P-type semiconductor

P-type semiconductors are materials engineered to have an abundance of positive charge carriers, known as 'holes'. Holes are vacancies left by electrons in the valence band of the semiconductor.
These holes can be visualized as the absence of an electron where it would typically reside and they effectively act as positive charges. To create a P-type semiconductor, a process known as 'doping' is used, where a small amount of trivalent impurity, such as boron, is added to the semiconductor's base material, typically silicon or germanium.

• Doping creates more positive charge carriers compared to negative ones.
• The presence of these holes facilitates the flow of electrical current, as neighboring electrons can move to fill these vacancies.
• This ability to conduct charge through holes is central to the behavior of P-type semiconductors in electronic devices.

The utility of P-type semiconductors becomes apparent when they are combined with N-type semiconductors to form p-n junctions, vital for electronic components like diodes.

N-type semiconductor

In contrast to P-type, N-type semiconductors are rich in negative charge carriers, specifically electrons. This is achieved by adding impurities called donors, which typically have five valence electrons. Common dopants for N-type semiconductors are elements like phosphorus or arsenic.

• These extra electrons increase the semiconductor's ability to conduct current.
• Unlike holes in P-type semiconductors, electrons in N-type semiconductors function as the main charge carriers, facilitating electron flow.
• In their natural state, N-type semiconductors carry a net negative charge due to the excess of electrons.

When an N-type semiconductor is joined with a P-type semiconductor, it enables the essential characteristics of devices like p-n junctions, allowing for advanced functionalities in electronic circuits.

Depletion region

The depletion region is a critical concept when discussing p-n junctions. It forms at the interface where P-type and N-type semiconductors meet. This region is crucial because it's devoid of any free charge carriers, such as electrons or holes.
When P-type and N-type materials are combined, electrons from the N-side fill in the holes on the P-side, an interaction known as recombination.

• This recombination leaves behind immobile ions with fixed charges, resulting in a zone depleted of carriers.
• The absence of charge carriers creates an electric field within the depletion region.
• This electric field acts as a barrier to prevent further electron flow from the N-side to the P-side without external voltage.

The depletion region, therefore, plays a pivotal role in the operation of semiconductor devices, influencing how they conduct current when voltage is applied.

Charge carriers

Charge carriers are particles that carry electric charge and facilitate current flow in semiconductors. In semiconductors, these carriers are mainly electrons and holes.
Electrons, being negatively charged, serve as the primary charge carriers in N-type semiconductors, while holes, acting as positive charges, are the main carriers in P-type semiconductors.

• Movement of these charge carriers in a semiconductor circuit results in current flow.
• The balance and interaction between electrons and holes are crucial for the functioning of semiconductor devices.
• The behavior of these carriers under various conditions and influences determines the electrical properties of semiconductor materials.

Their reliable management is integral to modern technology, as it underpins the functionality of key components like diodes and transistors.