A diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.). The diode has two electrodes, the positive pole, also called the anode; the negative pole, also called the cathode, when a forward voltage is applied between the two poles of the diode, The diode conducts, and when a reverse voltage is applied, the diode turns off. The on and off of the diode is equivalent to the on and off of the switch.Discrete Semiconductor Modules

A diode, also known as a diode, is an electronic device with two terminals with asymmetric conductance. The diode has unidirectional conductivity, and the direction of current is from the anode to the cathode through the tube when it is turned on.

Diode is one of the earliest semiconductor devices, and its application is very wide. Especially in various electronic circuits, the use of diodes and resistors, capacitors, inductors and other components for reasonable connection to form circuits with different functions can realize rectification of alternating current, detection of modulation signals, amplitude limiting and clamping, and control of power supplies. Voltage regulation and other functions.

After the discovery of semiconductor properties, semiconductor diodes became the world's first semiconductor devices. Today's diodes are mostly produced using silicon, although other semiconductor materials such as germanium are sometimes used. In the most common configuration today, a junction chip with semiconductor properties is connected to two electrical terminals through a PN junction.

Ⅰ. Types of Discrete Semiconductors-Diodes

1. Classified by material and development period:

Diode Vacuum Tube: Known as a vacuum tube or vacuum diode, it is a device used in early electronics. The working principle of a diode vacuum tube is based on the thermionic emission effect, whereby electrons heated in a hot cathode are released from the surface. When the hot cathode is heated to a certain temperature, a large number of free electrons are emitted. These free electrons are attracted by the electric field of the accelerator pole, form electron flow, and cross to the anode through the space in the vacuum. Since there is a unidirectional electrical barrier between the anode and the hot cathode, only electrons emitted from the hot cathode can flow to the anode, preventing the flow of reverse current.

Germanium diode: It is a diode made of Ge semiconductor material. It has a structure similar to other diodes, including an N-type germanium region and a P-type germanium region, formed by a PN junction of germanium material. Germanium diodes have a lower forward voltage drop (around 0.2-0.3V), which makes them advantageous in some applications. Germanium diodes have faster switching speeds and recovery times than some silicon diodes.

Selenium diode: It is a diode made of Se semiconductor material. Selenium diodes are similar in structure and operation to other diode types, with one P-type Selenium region and one N-type Selenium region. Selenium diodes have a relatively low frequency response and are generally suitable for low frequency applications. They have limited use in low frequency circuits such as some power supplies and audio amplifiers. The forward resistance of the selenium diode is relatively high, generally between tens and hundreds of ohms. This means that the selenium diode introduces a certain resistance in the circuit, and it is necessary to pay attention to the voltage and power consumption in the circuit design.

Silicon diode: It is a diode made of Si semiconductor material. It is one of the most common and widely used diode types and has many important properties and applications. Silicon diodes are similar in structure and operation to other diode types. It consists of a P-type silicon region and an N-type silicon region, forming a PN junction. Silicon diodes can be used as switches in protection circuits against reverse current flow. For example, when an inductive element in a circuit generates a reverse voltage, a silicon diode can direct this reverse voltage back to a power supply or ground to protect other electronic components.

Gallium arsenide diode: It is a diode made of GaAs semiconductor material. GaAs diodes have high mobility and short carrier lifetimes, giving them fast switching speeds and fast recovery characteristics. GaAs diodes have a low noise figure, which makes them advantageous in applications such as low-noise amplifiers and receivers.

2. Classification by application and characteristics:

Schottky diode: The rectification effect of the "Schottky effect" that utilizes the junction of both metal and semiconductor. Due to the low forward cut-in voltage and short turn-on recovery time, it is suitable for high-frequency rectification. Schottky diodes have better high temperature characteristics than other diode types. They are capable of operating in high temperature environments with less performance degradation at high temperatures. Since the Schottky diode has no carrier injection and a small amount of storage effect of the PN junction, it has a lower reverse recovery charge.

Photodiode: Light is injected into the PN junction, and a large number of holes in the P region and electrons in the N region are generated to generate a voltage (photoelectric effect). By measuring this voltage or current, it can be used as a light sensor. There are PN, PIN, Schottky, APD and other types. Solar cells also use this effect. Photodiodes convert light signals into electrical signals. When light hits a photodiode, the photon's energy is absorbed, creating electron-hole pairs. These carriers are separated in the PN junction, and a current or voltage signal is generated through an external circuit to realize photoelectric conversion.

PN junction diode: Apply forward bias and use the rectification properties of PN junction in semiconductors. It is the most basic semiconductor diode. It is commonly used in rectification and in parallel with inductors to protect other devices. PN junction diodes have unidirectional conduction characteristics. When a forward bias voltage is applied, that is, a positive voltage is applied to the P region and a negative voltage is applied to the N region, the current can flow from the P region to the N region, forming a conduction state. Under the reverse bias voltage, that is, the reverse voltage is applied to the P region, and the forward voltage is applied to the N region, the PN junction will form an electric potential barrier, which hardly allows current to pass through, and is in an off state.

Zener diode: When a reverse bias is applied, the reverse breakdown voltage that occurs when a certain voltage is exceeded changes little with the reverse current, and has a certain voltage stability capability. Devices made using this property are used as voltage references. The breakdown voltage (destruction voltage) is determined by the type and concentration of the dopant. Its forward bias is the same as that of a normal diode. The Zener diode can provide a stable voltage in the reverse breakdown state. When the reverse voltage exceeds the Zener voltage, the Zener diode will limit the voltage rise so that the voltage in the circuit remains at a stable value. This makes Zener diodes often used as voltage regulators, protecting other electronic components from excessive voltage. The breakdown voltage characteristics of Zener diodes make them useful in certain noise-limited applications. It can be used to limit the noise voltage in the circuit, providing a more stable and reliable signal.

Light Emitting Diode (LED): A diode that emits light when forward biased. From the types and characteristics of light emission, there are infrared diodes, visible light diodes of various colors, ultraviolet diodes, etc. LEDs have a long lifespan, usually reaching tens of thousands of hours or more. LEDs have fast turn-on and turn-off response times, making them suitable for applications requiring fast switching and dimming. LEDs consume less power than traditional light sources. They can work with lower energy consumption under the same brightness, contributing to energy saving and carbon emission reduction.

Varactor diode: When reverse bias is applied, the thickness of the depletion layer of the PN junction of the diode will change due to different voltages, resulting in a change in electrostatic capacitance (junction capacitance), which can be used as a variable capacitor controlled by voltage. The capacitance of a varactor diode is variable by changing the reverse bias voltage applied to the diode. This allows it to be used as a substitute for capacitors in circuits to achieve frequency tuning and filtering functions for circuits. Varactor diodes are often used as key components in voltage controlled oscillators. By changing the reverse bias voltage to adjust the capacitance of the diode, thereby changing the oscillation frequency.

PIN Diode: A PIN diode is a special type of diode that consists of layers of P-type (positive) semiconductor, I-type (undoped) semiconductor, and N-type (negative) semiconductor. It gets its name from the structure of these three layers: P-I-N. A high-resistance semiconductor layer between PN increases the accumulation effect of minority carriers, and the reverse recovery time is also longer. Utilizing the property that high-frequency signals are easier to pass through when forward biased, it is used for frequency band switching and high-frequency switching of antennas. PIN diodes can also be used in optical amplifiers. Amplification of optical signals can be achieved by injecting current into the I-type layer. When light strikes the I-type layer of a PIN diode, the energy of the photons generates electron-hole pairs, and these carriers can be freely transported in the I-type layer due to the existence of the undoped state.

Laser Diode: A diode capable of producing a laser beam through stimulated radiation. It is a semiconductor laser that uses the special structure and electrical properties of semiconductor materials to achieve laser emission. Laser diodes are capable of generating laser radiation through current injection to achieve narrow, monochromatic and coherent laser beam output. Laser has high energy density, strong directivity and narrow spectrum characteristics. The laser diode has fast modulation characteristics, and the intensity and frequency of the laser can be changed by modulating the current.

Current diode: is a special type of diode whose working principle is based on the conduction and blocking of current. Current diodes are commonly used in current control and protection circuits. When a voltage in the forward direction is applied, a constant current can be obtained regardless of the voltage. The usual current capacity is in the range of 1~15mA. Although it is called a diode, its structure and operating principle are similar to those of a junction field effect transistor. Current diodes can be used to control the flow of current in a circuit. It can limit the direction of current flow, so that the current can only pass in a specific direction. Current diodes have fast turn-on and turn-off response times and are therefore suitable for applications requiring fast protection and control of current flow.

Ⅱ. Working principle of discrete semiconductor-diode

Reverse Bias: When the reverse voltage is applied to the P region of the diode and the forward voltage is applied to the N region, a reverse bias state is formed. Under reverse bias, due to the formation of an electric potential barrier, electrons and holes are hindered by the electric potential barrier and can hardly pass through the PN junction. Therefore, in the reverse biased state, the diode has high resistance, which is called the cut-off state. Reverse breakdown occurs only when the reverse voltage exceeds the breakdown voltage of the diode, at which point the current breaks through the barrier.

Reverse Bias: When the reverse voltage is applied to the P region of the diode and the forward voltage is applied to the N region, a reverse bias state is formed. Under reverse bias, due to the formation of an electric potential barrier, electrons and holes are hindered by the electric potential barrier and can hardly pass through the PN junction. Therefore, in the reverse biased state, the diode has high resistance, which is called the cut-off state. Reverse breakdown occurs only when the reverse voltage exceeds the breakdown voltage of the diode, at which point the current breaks through the barrier.

Ⅲ. Application field of discrete semiconductor-diode

1. Circuit protection: Diodes can be used for circuit protection, such as reverse voltage protection diodes and overvoltage protection diodes, to prevent excessive voltage from damaging other electronic components.

2. Rectifier: As a key component of the rectifier, the diode converts the AC signal into a DC signal. They are commonly used in power supplies and electronic equipment such as power adapters, rectification circuits, and bridge rectifiers.

3. Signal detection and frequency mixing: Diodes can be used in signal detection and frequency mixing circuits. They can extract information from signals, or mix signals of different frequencies together.

4. Photoelectric conversion: Photodiodes (photodiodes) convert light energy into electrical energy, and are often used in photoelectric detection, optical communication, photoelectric sensing, and light measurement.

5. Logic gates and switches: Diodes can be used in logic gate circuits to realize logic functions. They also act as switches, controlling the flow of electricity.

6. Voltage regulation and voltage stabilization: Zener diodes (such as Zener diodes) can be used as voltage regulators and voltage regulators to maintain a stable voltage in circuits for applications such as power supply stabilization, voltage reference, and overvoltage protection.

7. Laser: Laser diode is a kind of semiconductor laser, used in laser printing, optical fiber communication, laser indication, laser cutting and other fields.

Ⅳ. Basic structure and constituent elements of discrete semiconductor-diode

1. PN junction: The junction between the P region and the N region is called a PN junction. The PN junction has special electrical properties, making the diode have unidirectional conduction characteristics.

2. P region (P-type semiconductor): The P region is a region of the diode, which is composed of a P-type semiconductor material. P-type semiconductors are materials formed by doping trivalent elements (such as boron, aluminum, etc.) with materials such as silicon or germanium. In the P region, the trivalent electrons of the impurity atoms form holes (positive charges), so the P region is positively charged.

3. N region (N-type semiconductor): N region is another region of the diode, which is composed of N-type semiconductor material. N-type semiconductors are materials formed by doping pentavalent elements (such as phosphorus, arsenic, etc.) into materials such as silicon or germanium. In the N region, the pentavalent electrons of the impurity atoms form excess electrons (negative charges), so the N region is negatively charged.TVS Diodes / ESD Suppressors

4. Packaging material: Diodes are usually packaged in a protective housing to provide mechanical protection and environmental isolation.

5. Metal leads or pads: Diodes usually have metal leads or pads that are used to connect to the circuit. These leads or pads provide the path for current to flow through the diode.

Ⅴ. Discrete Semiconductors - Current Regulation Diodes

Current Regulating Diode is a special type of diode, also known as constant current diode or constant current source diode. Its main function is to keep the current in the circuit at a constant level by stabilizing and regulating the current.Diodes - General Purpose, Power, Switching

Current regulation diodes provide a relatively stable current source through their special structure and material selection. Under suitable operating conditions, it is capable of producing a nearly constant current output over a range of voltages.

Current regulation diodes usually employ a feedback mechanism to achieve a constant current output. When the current exceeds the set value, the feedback mechanism automatically adjusts the resistance of the diode to dampen the change in current and keep it at a constant level.

Current regulation diodes typically have a low forward voltage drop, so they are useful in applications that require lower power dissipation and energy efficiency.

Frequently Asked Questions

1. How to identify the pins of the diode and connect them correctly?

Diodes usually have a package, which can be a glass tube, a plastic package, or a metal package, etc. Look for features such as markings, colors, and shapes on the case that may help identify the pins. Proper connection of the diode is done by identifying the anode and cathode of the diode either from the pin markings or from the data sheet. The anode is the positive side of the diode and is usually associated with the long lead. The cathode is the negative side of the diode and is usually associated with the short lead. Connect the diodes properly to the circuit. Connect the anode to the positive pole or power supply and the cathode to the negative pole or the ground point of the circuit.

2. What is the reverse recovery time of a diode?

The reverse recovery time of a diode refers to the time required for the current to change from a forward conduction state to an off state when the diode is switched from a forward biased state to a reverse biased state. When the diode is forward biased, an electrical barrier is formed at the PN junction, allowing current to flow. When the forward bias voltage suddenly changes to the reverse bias voltage, it takes a certain time for the electric potential barrier to be lifted, which causes the current to change from the forward conduction state to the cut-off state. This process is called the reverse recovery process and is measured by the reverse recovery time.