Diodes are semiconductor electronic components and are known for conducting electrical current in only one direction. They are usually made of semiconductor materials such as silicon, selenium or germanium. The main characteristics of these components include high efficiency, reliability and performance. Diodes play a fundamental role in electronic circuits and they have many different types, such as rectification diodes, Zener diodes, LEDs, Schottky diodes, photo-diodes and many others. Each type of diode is optimized for a specific application or function and has a wide range of uses in the electronics industry. Diodes are used in power conversion, regulation, light emission, detection, communication and many other fields. Their history has contributed to the development of electronic technology and the formation of many modern devices. Therefore, diodes have made important contributions to technology and human development.
What is a Diode?
Diodes are semiconductor electronic components and are known for transferring the current in only one direction. In other words, diodes allow current to flow in one direction in electrical circuits, while they prevent the flow of current in the opposite direction. They are usually made of semiconductor materials such as silicon, selenium or germanium. The P pole of the diode is called the “Anode”, and the N pole is called the “Cathode”. In diodes, current flows from the Anode end to the Cathode end.

History and Invention of the Diode
Diodes are semiconductor devices that transmit electrical current in only one direction and are used as a basic component in electronic circuits. The long history of diodes is based on fundamental studies in the field of electricity. Diodes have played a critical role in the development of electronic technology and are one of the basic electronic components that are still widely used today.

How Does the Diode Work?

Diodes are formed by combining a P-type and N-type semiconductor. At the P-N junction surface, the P-type substance attracts N-type electrons, and some of them fill the cavities of the P-type substance, forming a set. When a current is applied in the reverse direction this set expands. On the other hand, the current transition is achieved when a certain voltage level is reached (about 0.7 volts in silicon, 0.3 volts in germanium) after a current is applied in the right direction.
How are the Operating Characteristics and Voltage Values of Diodes Determined?
In order for the diode to pass a current while operating in the forward polarization (polarma) region, it is necessary to reach the threshold voltage specified by VF. Usually, this value is around 0.7V for silicon diodes and 0.3V for germanium diodes.
The diode does not pass current in the reverse polarization (polarma) region up to the maximum reverse voltage specified by VBR. When this value is exceeded, the diode gets in the breakdown zone, which means there is also a current flow through the diode in the opposite direction. For example, for a 1N4001 diode, this value is 50V.

Most diodes are made of semiconductor materials such as silicon, germanium or silicon. In order for the diode to start transmitting, sufficient voltage must be applied in the correct direction (from positive to negative). Usually, this voltage value is around 0.6V for diodes made of silicon material, and 0.3 V for diodes made of germanium material.
Structure and Working Principle of Diodes

- Anode (Positive Electrode): The anode, which is one end of the diode, receives or absorbs current through the diode. Anode is usually made of semiconductor materials such as silicon or germanium. Electrons flow through this electrode into the diode.
- Cathode (Negative Electrode): The cathode located at the other end of the diode allows current to exit the diode. After the electrons move through the diode, they reach the cathode and exit the circuit. The cathode usually has a larger size than the anode and is often made of a metal material.
- Semiconductor Material (P-N Connection): The semiconductor material inside the diode usually has a unified structure called a “P-N connection”. This is formed by combining P-type and N-type semiconductor materials together. A P-type semiconductor is a material in which electrons are less normally but more in case of a gap, while an N-type semiconductor consists of a material in which electrons are more normally but less in case of a gap. This P-N connection is an important component that provides the functionality of the diode.

The working principle of the diode is that the P-N connection forms a type of a scanning barrier, and the voltage required to overcome this barrier reaches the transmission threshold of the diode. The directional conductivity occurs when the positive end of the P-type semiconductor is connected at the cathode, while the inverse directional conductivity occurs when the negative end is connected at the cathode. In this way, the diode allows current passage only in a certain direction.
How is the Diode Robustness Test Performed?

The robustness test for the diodes can be performed using a digital multimeter. For this, a small voltage, sufficient to provide a straight polarma, is generated between the test leads. The normal voltage drop is usually between 0.5 and 0.8 V. The flat polarma resistance of a diode in good condition usually ranges from 1,000 ohms to 10 ohms. In the case of reverse polarization, the expression “OL” appears on the screen of the digital multimeter (this indicates that a very high resistance exists).

The current values have been assigned to the diodes. If this value is exceeded or the diode malfunctions, the diode may short circuit. Diodes can allow current to flow in both directions or stop the flow of current in both directions.

What are the Areas of Use and Types of Diodes?
Diodes have many varieties with different structures and properties. There are various types of diodes based on their functions and areas of application. Here are some types of diodes that are commonly used:
Rectifier Diodes: Rectifier diodes are used to convert alternating current (AC) to direct current (DC). These are usually simple diodes with unidirectional conductivity feature.

Bridge Diodes: A bridge diode is a circuit layout created by combining four diodes together. This layout forms a full bridge that combines currents in the opposite direction to each other and is usually used to convert AC (alternating current) signals to DC (direct current) signals. Bridge diodes are widely used in applications such as power supplies and rectification circuits.

Zener Diodes: Zener diodes become permeable with a phenomenon called “the zener effect” when a certain voltage value is reached. These properties allow them to be used in voltage regulation and protection circuits.

LEDs (Light Emitting Diodes): LEDs are the diodes that work on electro-luminescence principle. They function by emitting light when the current passes through, and the color of the light they emit depends on the properties of the semiconductor material used. The LEDs are widely used in applications such as lighting, instrument panels and displays.

Photodiodes: Photodiodes are the diodes that are sensitive to light. The light causes a current change in the PN connection of the diode, which is used to detect the light intensity and benefit from the photoelectric effect.

Tunnel Diodes: The tunnel diodes are special types of diodes used in high-frequency applications and work with a phenomenon called the tunneling effect.

Schottky Diodes: Schottky diodes are the diodes with a metal-semiconductor combination that allows for faster switching and low voltage drops. These properties allow them to be used in high-frequency applications and power supplies.

Varactor Diodes: Varactor diodes are types of diodes in which the capacitance in a PN connection is sensitive to a voltage change. With these properties, they are widely used in frequency modulated circuits and voltage controlled oscillators.

These are only “some” of the types of diodes, and there are many other types of diodes used in electronics industry. Each type of diode is optimized for a specific application or function.
What are the Contributions of Diodes to Technology and Human Development?
- Development of Electronic Circuits: Diodes are one of the basic components of electronic circuits and they enable the operation of many electronic devices. Computers, televisions, mobile phones, radios and many other electronic devices work with circuits containing diodes. Diodes allow these devices to be more efficient, more reliable and more compact.
- Power Rectifying and Regulation: Diodes play a fundamental role in rectifying circuits used to convert alternating current (AC) to direct current (DC). In addition, special types of diodes, such as Zener diodes, are used for voltage regulation and ensure stable operation of power supplies.
- Light Emitting Diodes (LEDs): LEDs are the light-emitting versions of diodes and are used in many lighting and displaying applications. LEDs offer lower energy consumption and longer service life compared to conventional light sources, which saves energy and reduces environmental impacts.
- Optical and Communication Technologies: Photodiodes are types of diodes that are widely used in optical communication and sensing applications. In optical fiber communication systems, the photodiodes are used to convert optical signals into electrical signals. This allows for fiber-optic communication technologies that offer high-speed data transmission.
- Security and Detection Applications: Photodiodes and sensor diodes are used in security systems, automotive sensors, industrial control systems and many other applications. These diodes can be used to detect light, temperature, motion and other environmental variables and form the parts of various automatic control systems.
- Solar Energy: The solar cells use photodiodes to convert sunlight into electrical energy. This contributes to the popularization and expansion of solar-powered systems, especially with the increasing use of renewable energy sources.
Diodes are used as a basic component in electronics, communication, lighting, energy and many other fields. Therefore, the contributions of diodes to technology and human development are very wide and important.