As an AI text-based model, I'm unable to draw graphical illustrations. However, I can describe the V-I characteristics of a p-n junction diode and answer your questions.
(i) V-I Characteristics of a p-n junction diode:
The V-I characteristics of a p-n junction diode represent the relationship between the voltage (V) applied across the diode and the resulting current (I) flowing through it. Here are the two regions of operation:
Forward Bias: In the forward bias configuration, the positive terminal of the voltage source is connected to the p-type material of the diode, and the negative terminal is connected to the n-type material. This arrangement allows the majority carriers (holes in the p-region and electrons in the n-region) to move towards the junction, reducing the barrier potential. As a result, the diode exhibits a low resistance to current flow, and a significant current starts to flow through it. The forward current (I) increases rapidly with a small increase in forward voltage (V) until it reaches a saturation point known as the forward current saturation.
Reverse Bias: In the reverse bias configuration, the positive terminal of the voltage source is connected to the n-type material, and the negative terminal is connected to the p-type material. This arrangement increases the barrier potential, preventing the majority carriers from crossing the junction easily. Therefore, only a small reverse current (called reverse leakage current) flows, which is typically in the range of nanoamperes or picoamperes. The reverse current remains relatively constant over a wide range of reverse voltages until a certain critical voltage is reached.
(i) Reason for reverse current independence up to the critical voltage:
The reverse current under reverse bias is almost independent of the applied potential up to a critical voltage due to the depletion region formed at the p-n junction. This region consists of immobile ionized impurities (positive ions in the n-region and negative ions in the p-region) that create an electric field across the junction, known as the built-in potential or barrier potential. The magnitude of this potential depends on the doping concentrations in the p and n regions.
Initially, under reverse bias, the applied potential opposes the built-in potential. This reduces the effective barrier potential, allowing a small reverse current to flow. However, as the reverse voltage is increased, the depletion region widens, resulting in an increased width of the barrier potential. This wider region prevents the majority carriers from easily crossing the junction, limiting the reverse current. Thus, until the critical voltage is reached, the reverse current remains almost constant because the depletion region's width dominates the current flow, not the applied voltage.
(ii) Reason for sudden increase in reverse current at the critical voltage:
When the applied reverse voltage exceeds the critical voltage (also known as the breakdown voltage or avalanche voltage), the electric field in the depletion region becomes so intense that it causes a phenomenon called avalanche breakdown. In this breakdown region, the covalent bonds within the depletion region are disrupted, creating a large number of electron-hole pairs. These carriers are accelerated by the electric field and contribute to an abrupt increase in the reverse current.
Name of a semiconductor device operating under reverse bias in breakdown regions:
A semiconductor device that operates under reverse bias in the breakdown region is known as a Zener diode. Zener diodes are specifically designed to exhibit a controlled breakdown at a particular voltage called the Zener voltage. They are used in various applications such as voltage regulation, overvoltage protection, and voltage reference circuits.
