Question

A P-N junction is said to be forward based when (A) a magnetic field is applied in the region of junction. (B) a potential difference is applied across \(\mathrm{P}\) and \(\mathrm{N}\) regions making \(\mathrm{P}\) region negative and \(\mathrm{N}\) region positive. (C) not potential difference is applied across \(\mathrm{P}\) and \(\mathrm{N}\) regions. (D) a potential difference is applied across \(\mathrm{P}\) and \(\mathrm{N}\) regions making P region positive and N region negative.

Short answer

A forward-based P-N junction is when the P region is connected to the positive terminal and the N region is connected to the negative terminal of a voltage source. Based on the given options, the correct answer is (D) a potential difference is applied across P and N regions making P region positive and N region negative.

Step-by-step solution

Option A: Magnetic field applied in the region of the junction

This option is not relevant to a forward-based P-N junction, as applying a magnetic field does not necessarily make a P-N junction forward-based. Therefore, option A is incorrect.

Option B: Potential difference making P region negative and N region positive

This option describes a situation where the P-N junction is reverse-biased, as the P region becomes negative and the N region becomes positive. A forward-based P-N junction requires the opposite situation where P region is positive and the N region is negative. Therefore, option B is incorrect.

Option C: No potential difference applied across P and N regions

When there is no potential difference applied across the P and N regions, the P-N junction will be unbiased. For a P-N junction to be forward-based, there must be a potential difference applied, making the P region positive and the N region negative. Therefore, option C is incorrect.

Option D: Potential difference making P region positive and N region negative

This option correctly describes a forward-based P-N junction. When a potential difference is applied across the P and N regions such that the P region is positive and the N region is negative, the P-N junction will be in forward bias. Therefore, option D is the correct answer.

Key concepts

Forward Bias

In semiconductor physics, when we talk about a P-N junction being in forward bias, we essentially mean applying a voltage across the junction in such a way that it promotes the flow of current. When a potential difference is applied where the P region is positive and the N region is negative, the electrons in the N region gain energy to cross over to the P region.
This setup reduces the barrier potential, allowing more charge carriers to flow through easily. The result is that the current flow across the junction increases, allowing the device to conduct electricity effectively.

• The P region is made positive by connecting it to the positive terminal of the battery.
• The N region is made negative by connecting it to the negative terminal of the battery.
• This arrangement decreases the width of the depletion region.
• It increases the flow of charge carriers across the junction.

Reverse Bias

A reverse-biased P-N junction is the opposite of forward bias. In this situation, the N region is connected to the positive terminal of the battery, while the P region is connected to the negative terminal.
This orientation increases the barrier potential and widens the depletion region, which inherently limits the flow of charge carriers across the junction, essentially blocking the flow of current.

• The P region becomes negative in relation to the N region.
• The depletion region widens, which acts as an insulator.
• The current flow is negligible except for a small reverse saturation current, mainly due to minority carriers.
• This mode is useful in applications like Zener diodes and photodiodes.

Potential Difference

In the context of P-N junctions, potential difference plays a crucial role in determining whether the junction is forward or reverse-biased.
Potential difference refers to the voltage applied across the P and N regions that affects the movement of charge carriers.

• In forward bias, the potential difference reduces the barrier energy, allowing charge carriers to move quickly across the junction.
• In reverse bias, the potential energy increases the barrier, impeding the flow of charge carriers and creating a high resistance path.
• The effect of potential difference on the conductive properties of the P-N junction is fundamental to its behavior in circuits.
• Device performance such as light-emitting diodes (LEDs) and rectifying diodes rely heavily on the applied potential difference.

Semiconductor Physics

Semiconductor physics forms the base knowledge required to understand P-N junctions, which are critical building blocks of electronic components.
Semiconductors are materials with electrical properties that fall between conductors and insulators, with silicon being the most commonly used.

• Semiconductors have a valence band and conduction band separated by a relatively small energy gap.
• Doping, the introduction of impurities, allows control over the electrical properties, creating either P-type or N-type materials.
• The P-N junction in semiconductor physics is formed by combining P-type and N-type materials.
• This junction displays unique properties allowing it to control electron flow, making it essential in diodes, transistors, and other devices.