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Chapter 34: Problem 23

In a \(p-n\) junction diode, holes diffuse from the \(p\) -region to the \(n\) -region because: (a) the free electrons in the \(n\) -region attract them (b) they are swept across the junction by the potential difference (c) there is greater concentration of holes in the \(p\) -region as compared to \(n\) -region (d) none of the above

Short Answer

Expert verified
The correct answer is (c) due to concentration gradients.

Step by step solution

01

Understanding the Problem

In a p-n junction diode, understanding the movement of charge carriers is crucial. We need to determine why holes, which are positive charge carriers, move from the p-region to the n-region.
02

Option Analysis (a)

Option (a) suggests that the free electrons in the n-region attract the holes from the p-region. While forces between opposite charges exist, the primary reason for diffusion is not just attraction by free electrons.
03

Option Analysis (b)

Option (b) claims that holes are swept across the junction by the potential difference. However, at equilibrium, the potential difference actually acts to prevent further movement of charge carriers, forming a depletion region.
04

Option Analysis (c)

Option (c) asserts that there is a greater concentration of holes in the p-region compared to the n-region. This difference in concentration is the primary reason for diffusion; holes naturally move from a region of higher concentration to lower concentration.
05

Option Analysis (d)

Option (d) states that none of the above options are correct. However, analysis of option (c) shows that it accurately describes the diffusion process due to concentration gradients.
06

Conclusion

The movement of holes from the p-region to the n-region is primarily driven by the concentration gradient, where holes move from high to low concentration. This corresponds to the explanation provided in option (c).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Charge Carriers
In a p-n junction diode, charge carriers play a vital role. Charge carriers are essentially particles that carry electric charge within a semiconductor. In the context of a p-n junction, there are two main types of charge carriers:
  • Electrons: These are negatively charged particles that dominate the n-region of the diode.
  • Holes: These are positively charged quasi-particles, found predominantly in the p-region.
The movement of these charge carriers is essential for current flow in semiconductors. When a p-n junction is formed, electrons from the n-region and holes from the p-region start to move and cross the junction. This movement of charge carriers is largely influenced by several factors, including concentration gradients and electric fields.
Diffusion
Diffusion is a fundamental process in a p-n junction diode that describes the movement of charge carriers from a region of high concentration to a region of low concentration. This process occurs naturally due to the inherent kinetic energy within particles, motivating them to spread out and reach equilibrium.
  • In the p-n junction, diffusion happens as holes move from the p-region, where their concentration is high, into the n-region, where hole concentration is lower.
  • Similarly, electrons tend to diffuse from the n-region into the p-region.
Through diffusion, charge carriers are redistributing themselves across the junction, which is critical to establishing equilibrium in the device.
Concentration Gradient
The concentration gradient is a key driving force for the diffusion of charge carriers in a p-n junction diode. It refers to the difference in the number of charge carriers (holes and electrons) between the p-region and n-region.
  • In a typical p-n junction, the p-region contains a higher concentration of holes compared to the n-region.
  • Conversely, the n-region has more electrons than the p-region.
This imbalance creates a gradient, prompting charge carriers to move toward the region with fewer particles of the same type. Holes naturally move towards the n-region, while electrons move towards the p-region until equilibrium is reached.
Depletion Region
The depletion region is a crucial area in a p-n junction diode where no free charge carriers exist. As diffusion occurs, electrons and holes recombine near the junction. This recombination diminishes free charge carriers, forming the depletion region. Key characteristics include:
  • It acts as an insulating layer, preventing further charge carrier movement across the junction after initial recombination.
  • The electric field created within the depletion region opposes further movement of excess carriers from both regions.
The depletion region ensures that a p-n junction diode doesn't conduct electric current in equilibrium, yet it primes the device for forward bias conduction when an external voltage is applied.

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Most popular questions from this chapter

The band gap for a pure semi-conductor is \(2.1 \mathrm{eV}\). The maximum wavelength of a photon which is able to create a hole- electron pair is : (a) \(600 \mathrm{~nm}\) (b) \(589 \mathrm{~nm}\) (c) \(400 \mathrm{~nm}\) (d) none of these

Assume that the number of hole-electron pair in an intrinsic semi-conductor is proportional to \(e^{-\Delta E / 2 k T}\). Here, \(\Delta E=\) energy gap and \(\quad k=8.62 \times 10^{-5} \mathrm{eV} / \mathrm{kelvin}\) The energy gap for silicon is \(1.1 \mathrm{eV}\). The ratio of electronhole pairs at \(300 \mathrm{~K}\) and \(400 \mathrm{~K}\) is : (a) \(e^{-5.31}\) (b) \(e^{-5}\) (c) \(e\) (d) none of these

In case of \(p-n\) junction diode at high value of reverse bias, current rises sharply. The value of reverse bias is called : (a) cut off voltage (b) inverse voltage (c) zener voltage (d) critical voltage

A signal of \(20 \mathrm{mV}\) is applied to common emitter transistor amplifier circuit. Due to this, the change in base current and the change in collector current are \(20 \mu \mathrm{A}\) and \(2 \mathrm{~mA}\). The load resistance is \(10 \mathrm{k} \Omega\). The voltage gain is: (a) \(20 \mathrm{~V}\) (b) \(10 \mathrm{~V}\) (c) \(50 \mathrm{~V}\) (d) none of these

Semi-conductor devices are (a) temperature dependent (b) current dependent (c) voltage dependent (d) none of the above
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