What is a Semiconductor Diode and What are its Characteristics?
A semiconductor, as the name mentions, is an element that bears partial conducting ability. A semiconductor does neither fit itself under the category of conductors nor under the category of the insulator. Generally, some impurities are always added to the semiconductor for the best results. This process is commonly termed doping. Based on the type of impurity, semiconductors are further categorized into two types- a) p-type semiconductor (positively charged) and b) n-type semiconductor (negatively charged). P and N-type semiconductors have limited usage when they are used in isolation. But when we make a collaborative usage for both p and n-type semiconductors, it is called a p-n junction.
When a p-n junction is affixed to some external voltage provider, for instance, a battery, the complete set-up will be known as a Semiconductor Diode. Though the entire set-up is bi- terminal, the passage of current is unidirectional.
Types of Semiconductors
Semiconductors are classified under two heads based on the connection used:-
Semiconductor Diode Forward Bias: It is a very well-known fact that a battery has two terminals- a positive terminal and the other negative one. So, when the semiconductor's N and P end is fixed with the negative and positive sides of the battery, respectively, the set-up is coined as Semiconductor Diode forward bias. Since the negative extreme will drive away free electrons in the front of the junction, and the P end of the semiconductor will thrust the holes, they will merge at the junction. But free electrons coming out of the battery will penetrate the N region, and the valence electrons abandon the P region, thus creating a movement of current.
Semiconductor Diode Reverse Bias: As the name suggests, it is just the opposite concept of forwarding bias. Now, the semiconductor's N side is affixed with the positive end of the battery. This entire set-up is known as Semiconductor Diode reverse bias. The electrons that arise from the N side of the semiconductor will be directed along with the positive terminal of the battery. The negative terminal will drive the holes away from the junction. The holes and electrons do never meet at the junction, and there is a clog of current in this setup. As we can see, the majority current does not flow in the reverse bias. Instead, there is a reverse flow of current in this situation due to minority carriers.
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Symbol of the Circuit
There are certain symbols used to express an electrical circuit. Following the above discussions, we can create a symbol of the Semiconductor Diode. It is represented as:-
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Semiconductor Diode Characteristics
There is a graphical representation of the voltage and current, as applied in the case of Semiconductor Diode forward bias and Semiconductor Diode reverse bias. When a forward bias is raised, we also observe a rise in current up to a stable voltage called knee voltage in a linear fashion. But after this voltage, the current differs in a non-linear way.
As we know, reverse current does not depend on the reverse bias. Rather this current depends on the temperature of the junction. It is calculated that the current multiplies to the extent of 7% for every 1-degree rise in temperature.
Zener Breakdown
If the reverse bias is raised to a large extent, the electric field also gets expanded, which in turn creates a huge number of electrons and holes. It is defined as a Zener breakdown.
Dynamic Resistance
It is explained as the ratio of minor changes in the voltage to the ratio of minor changes in the current. It is expressed in the form of rd. Therefore the numerical expression of voltage resistance is rd = \[\frac {\Delta V} {\Delta I}\]
Numerical:- A diode is made constant in a circuit. The voltage falls by 0.5 V, and the highest power marked is 100 mW. What should be the value of the resistor R, which is attached in series to this diode?
Solution:- Current that flows among the diode the, I = \[\frac {Power} {Voltage}\]
Therefore, I= \[\frac {(100 \times 10^-3)} {0.5V}\]
(as we know 1mW= 10-3 W)
= 0.2 A
Resistance=Net Voltage/Current \[\frac {Net Voltage} {Current}\]
= \[\frac { (1.5−0.5)} {0.2}\]
= 5 Ohm.
The devices made from semiconductors have very much eased our lives. There are different types of diodes like the Semiconductor Diode that are used in many devices. So, it becomes important for us that we know about these devices in detail. The motive of this article is the same i.e it is meant to give you in-depth detail on the Semiconductor Diode. You will be able to study the definition of Semiconductor Diode, its different characteristics and its symbol.
Diode
A diode is a semiconductor device made up primarily of silicon components. The anode, which is inherently positive and has a lot of holes, is positioned next to the cathode, which is negatively charged and contains a lot of electrons. A depletion area forms at this point, with no holes or electrons. A positive anode voltage causes the depletion region to be small, allowing current to flow; a negative anode voltage causes the depletion region to be big, prohibiting current flow.
A diode is a two-terminal electrical component that conducts electricity mostly in one direction. It has a strong resistance on one end and a low resistance on the other.
To limit the voltage across circuits or to convert AC into DC, diodes are used. They also serve to safeguard the circuits. The most common semiconductors used to manufacture diodes are silicon and germanium. Although they both transport electricity, in the same way, however, how they do so, differs. Diodes are available in a range of shapes and sizes, each with its own set of uses.
Diode Construction
The two semiconductor materials that can be utilized to manufacture diodes are silicon and germanium. When the anode voltage exceeds the cathode voltage and the diode conducts readily with minimum voltage loss, it is said to be forward-biased. When the cathode voltage exceeds the anode voltage, the diode is said to be reverse-biased. The direction of conventional current flow is depicted by the arrow in the symbol.
Diode's Symbol
The anode and cathode are the two terminals of a diode. The anode is represented by the arrowhead. In the forward-biased condition, the anode represents the traditional current flow direction. The cathode is represented by the vertical bar.
The following are some of the most commonly used and essential diodes:
Tunnel Diode
Because of the quantum mechanical process known as tunneling, a tunnel diode (also known as an Esaki diode) has essentially zero resistance. In tunnel diodes, the PN junction is heavily doped and about 10 nm wide. The n-side conduction band electron states are more or less aligned with the p-side valence band hole levels, resulting in a broken bandgap.
Zener Diode
The most valuable sort of diode is the Zener diode, which can provide a constant reference voltage. When a specific voltage is supplied, these are reverse biased and break down. When the current flowing through the resistor is limited, a stable voltage is formed. Zener diodes are often used in power supplies to provide a reference voltage.
LED (Light Emitting Diode)
A photodiode can detect even a little amount of current flow induced by light. Even a small amount of current flow caused by light can be detected by a photodiode. When it comes to detecting light, these are incredibly useful. Photodiodes are reverse bias diodes that are commonly found in solar cells and photometers. They're even used in the generation of electricity.
FAQs on Semiconductor Diode
1. What is a semiconductor, and how are p-type and n-type semiconductors created for use in diodes?
A semiconductor is a material, like silicon or germanium, with electrical conductivity between that of a conductor and an insulator. Its conductivity can be precisely controlled. To create different types for a diode, a process called doping is used:
- n-type Semiconductor: A pure semiconductor is doped with pentavalent impurities (e.g., phosphorus). These atoms add excess free electrons, making electrons the majority charge carriers.
- p-type Semiconductor: A pure semiconductor is doped with trivalent impurities (e.g., boron). This creates an excess of 'holes' (electron vacancies), making holes the majority charge carriers.
2. What exactly is a semiconductor diode and what is its most fundamental purpose in an electronic circuit?
A semiconductor diode is a two-terminal electronic component created by joining a p-type and an n-type semiconductor to form a p-n junction. Its most fundamental purpose is to allow electric current to flow easily in one direction while severely restricting its flow in the opposite direction. This property of unidirectional current flow makes it act like a one-way valve for electricity.
3. How does a p-n junction form a depletion region, and why is this region critical for a diode's function?
When a p-type and n-type semiconductor are joined, electrons from the n-side diffuse to the p-side and holes from the p-side diffuse to the n-side. This diffusion and recombination of charge carriers near the junction leaves behind immobile positive and negative ions. This creates a thin layer called the depletion region, which is free of mobile charge carriers and has a natural potential difference called the potential barrier. This barrier is critical because it opposes further movement of charge, and it must be overcome by an external voltage for the diode to conduct current.
4. What is the difference between forward biasing and reverse biasing a semiconductor diode?
The key difference lies in how the external voltage is applied across the p-n junction:
- Forward Biasing: The positive terminal of the voltage source is connected to the p-side and the negative terminal to the n-side. This opposes the potential barrier, narrows the depletion region, and allows a large current to flow once the voltage exceeds the barrier potential (knee voltage).
- Reverse Biasing: The negative terminal is connected to the p-side and the positive terminal to the n-side. This supports the potential barrier, widens the depletion region, and allows only a very small leakage current to flow due to minority charge carriers.
5. How does a semiconductor diode's one-way current flow allow it to work as a rectifier?
Rectification is the process of converting alternating current (AC) into direct current (DC). An AC signal continuously reverses its polarity. When this signal is applied to a diode, the diode enters forward bias during one half of the cycle, allowing current to pass. During the other half of the cycle, the polarity reverses, the diode enters reverse bias, and it blocks the current flow. As a result, only half of the AC waveform passes through, creating a pulsating DC output. This is the fundamental principle of a half-wave rectifier.
6. What are some important special-purpose semiconductor diodes and their main applications as per the CBSE 2025-26 syllabus?
Beyond basic rectification, several special-purpose diodes are designed for specific functions:
- Zener Diode: Designed to operate in reverse breakdown region. Its primary application is as a voltage regulator to provide a stable voltage.
- Light Emitting Diode (LED): Converts electrical energy into light energy when forward biased. It is used in displays, indicators, and lighting.
- Photodiode: Converts light energy into electrical energy. It operates in reverse bias and is used as a photodetector in optical communication and sensors.
- Solar Cell: A large-area p-n junction diode that converts solar radiation directly into electrical energy without any biasing.
7. Why is a semiconductor diode considered a non-linear device, unlike a simple resistor?
A simple resistor is a linear device because it follows Ohm's Law (V = IR), where the current is directly proportional to the applied voltage, resulting in a straight-line V-I graph. A semiconductor diode is non-linear because its current-voltage relationship is not proportional. In forward bias, the current is negligible until the voltage reaches the knee voltage, after which it increases exponentially. In reverse bias, the current is almost zero. This non-proportional, exponential relationship makes its V-I characteristic curve non-linear.
8. How is a semiconductor diode represented in a circuit diagram, and what do its symbols signify?
In a circuit diagram, a semiconductor diode is represented by a symbol consisting of a triangle pointing towards a vertical line.
- The triangle represents the p-type region, known as the anode. The direction of the triangle also indicates the direction of conventional current flow.
- The vertical line represents the n-type region, known as the cathode.
