What is a semiconductor and what are its uses

A semiconductor is a substance with a conductivity between that of a conductor and an insulator. It is not very conductive in a pure state, but its conductivity can be adjusted by adding impurities (doping) or changing the temperature. The typical representative of semiconductors is silicon, which is widely used in the manufacturing of electronic components. Semiconductor technology is the cornerstone of modern electronic devices, such as smartphones, computers, digital cameras, etc., which rely on semiconductor chips. In addition, semiconductors are also very important in the energy field, such as semiconductor materials, which are the core of solar cells. The application of semiconductors also includes LED lighting, sensors for medical equipment, and power electronic devices, which have had a profound impact on modern technology and daily life.

Definition of Semiconductors

1.1 Basic concepts and properties

Semiconductors are materials that lie between conductors and insulators, and their conductivity varies with temperature. At room temperature, the resistance value of a semiconductor is between that of a conductor (such as copper, silver) and an insulator (such as rubber, quartz). Its characteristic is that under certain conditions, such as heating or exposure to light, its conductivity will be enhanced. This characteristic makes semiconductors widely used in electronic devices.

1.2 Comparison with conductors and insulators

Conductors: usually refer to metals or other substances with very low resistance values, which can easily conduct electric currents. For example, the resistance values of copper and silver are 1.68x10 ^ -8 and 1.59x10 ^ -8 ohms · meters at 20 ° C, respectively.

Insulators: These materials have very high resistance values and are almost non-conductive. For example, the resistance value of clean quartz is approximately 1x10 ^ 17 ohms per meter.

Semiconductor: Between conductors and insulators. For example, the resistance value of pure silicon at room temperature is about 2.3x10 ^ 3 ohms · meter, but its resistance value will significantly decrease when exposed to light or heating.

Classification of Semiconductors

2.1 Intrinsic semiconductor

Intrinsic semiconductor refers to pure, undoped semiconductor materials. Their conductivity is determined by their own lattice structure and does not depend on external dopants.

Features:

The intrinsic semiconductor is almost an insulator at absolute zero.

As the temperature increases, its conductivity gradually increases.

Pure silicon and pure germanium are common intrinsic semiconductors.

Parameters:

Band gap of pure silicon: 1.12 eV

Band gap of pure germanium: 0.66 eV

2.2 Doped semiconductor

The process of changing the electrical properties of a semiconductor by adding a small amount of impurity elements is called doping. These impurity elements are called dopants.

2.2.1 P-type semiconductor

Definition: When trivalent elements, such as boron (B) or gallium (Ga), are doped into a semiconductor, a P-type semiconductor is formed.

Features:

Excess valence electrons form "holes".

Holes can accept electrons, hence they are called "hole type".

Has a positive charge.

Common doping materials: boron (B), gallium (Ga).

Doping concentration: The common doping concentration is 10 ^ 15 to 10 ^ 18 impurity atoms per cubic centimeter.

2.2.2 N-type semiconductor

Definition: When pentavalent elements are doped into semiconductors, such as phosphorus (P) or arsenic (As), N-type semiconductors are formed.

Features:

The excess valence electrons increase the number of free electrons.

Free electrons are the main charge carriers.

Has a negative charge.

Common doping materials: phosphorus (P), arsenic (As).

Doping concentration: The common doping concentration is 10 ^ 15 to 10 ^ 18 impurity atoms per cubic centimeter.

The working principle of semiconductors

3.1 Band theory

The band theory is the fundamental theory for explaining the electrical properties of solid materials. In this theory, the energy of electrons is limited to a specific range or "band".

Valence band: The energy band in a solid that is completely filled with electrons and has the highest energy.

Features:

It is located below the band gap.

At 0K, the valence band is completely filled with electrons.

Electrons do not have enough energy to transition from the valence band to the conduction band.

Conduction band: an energy band in a solid that can be occupied by electrons, but has not yet been occupied by electrons at T=0K.

Features:

It is located above the price band.

At 0K, the conduction band is empty.

When electrons gain sufficient energy, they can transition from the valence band to the conduction band and participate in conductivity.

Band gap: The difference between the lowest energy of the conduction band and the highest energy of the valence band.

Parameters:

Band gap of silicon: 1.12 eV

Energy band gap of germanium: 0.66 eV

3.2 The working mechanism of P-N junction

The P-N junction is the junction between P-type semiconductors and N-type semiconductors.

Formation:

When P-type and N-type semiconductors combine, P-type holes and N-type free electrons will combine at the junction, forming a "depletion layer" or "space charge region".

Features:

There are no free charge carriers in this region, so it is non-conductive.

An internal electric field is formed in this region, causing electrons to move from the N region to the P region, while holes move from the P region to the N region.

Work:

When an external voltage is applied to the P-N junction, such as a positive bias voltage, it will cancel out the internal electric field, allowing charge carriers to pass through and conduct electricity.

When a reverse bias voltage is applied, the internal electric field is enhanced, further preventing the passage of charge carriers and thus non-conductive.

The Use of Semiconductors

4.1 Information processing and storage

Semiconductor technology plays a core role in the fields of information processing and storage.

4.1.1 microprocessor

Purpose: A microprocessor is the brain of computers and other digital systems, responsible for processing instructions and controlling data flow.

Performance parameters:

Processing speed: measured in GHz, modern microprocessors generally operate in the range of 1-5 GHz.

Energy efficiency ratio: The ratio of processor performance to power consumption, which is important for mobile devices and data centers.

Number of cores: A multi-core processor can handle multiple tasks simultaneously, improving overall performance.

Integration: The development of process technology allows microprocessors to integrate more transistors, promoting performance improvement.

4.1.2 Storage devices

Purpose: Used for storing data, including random access memory (RAM) and read-only memory (ROM).

Performance parameters:

Storage capacity: The unit is usually GB or TB, which determines the amount of data that a storage device can store.

Read and write speed: affects the speed of data access and transmission.

Power consumption: Especially on mobile devices, low power storage is more favored.

Physical size: Small size memory is suitable for portable devices.

4.2 Sensing and Detection

Semiconductor sensors are widely used in various fields such as temperature, light intensity, and pressure.

Features:

Sensitivity: The degree to which a sensor responds to external changes.

Accuracy: The measurement accuracy of the sensor.

Stability: The degree of stability of sensor performance during long-term use.

4.3 Power supply and energy conversion

Semiconductor technology plays a crucial role in energy conversion and power management.

4.3.1 solar cell

Purpose: To convert solar energy into electrical energy.

Performance parameters:

Conversion efficiency: usually between 15% and 22%, which determines the energy conversion efficiency of the battery.

Cost: Manufacturing costs are crucial for the popularization of solar cells.

Lifetime: The expected service life of solar cells is usually 20-25 years.

4.3.2 Power electronic devices

Purpose: To control and convert electrical energy in power systems.

Features:

Efficiency: High efficiency means less energy loss.

Size: miniaturized devices are beneficial for portability and space savings.

Stability: High stability ensures long-term reliable operation.

4.4 Optoelectronic Technology 

The application of semiconductors in optoelectronic technology is increasing day by day.

4.4.1 laser

Usage: Widely used in fields such as communication, medical, and industrial processing.

Performance parameters:

Wavelength: determines the purpose and penetration power of the laser.

Power: affects the cutting ability and transmission distance of the laser.

Size: Small laser suitable for compact equipment.

4.4.2 Photodetector

Usage: Used for detecting optical signals, applied to cameras, optical communication, etc.

Performance parameters:

Sensitivity: The degree to which a detector responds to light signals.

Speed: The response speed determines the rate of signal processing.

Stability: Ensure long-term accurate optical signal detection.

The importance of semiconductors in modern technology

5.1 The driving role of the electronics industry

Semiconductor technology is the core of the development of the electronics industry, and its importance is reflected in the following aspects:

Innovation driven: The progress of semiconductor technology has driven the revolution in the fields of computers, smart phones and the Internet, providing a platform for new generation technology innovation.

Performance improvement: With the advancement of semiconductor technology, the processing speed, energy efficiency, and integration of electronic products continue to improve, making them more powerful, efficient, and smaller in size.

Cost reduction: The increase in semiconductor integration predicted by Moore's Law has led to a continuous decrease in the cost per unit function, promoting the popularization of electronic products.

Industry impact:

Consumer electronics: The continuous improvement in performance of products such as smartphones, televisions, and personal computing devices.

Business computing: The development of technologies such as data centers and cloud computing relies on high-performance and efficient semiconductor products.

5.2 The impact on new energy technologies

Semiconductor technology is equally crucial for the development of the new energy field:

Energy conversion efficiency: The efficiency improvement of solar cells and other new energy conversion equipment reduces the cost difference of renewable energy compared to traditional fossil fuels.

Electric vehicles: The advancement of semiconductor technology has driven the development of motor controllers and battery management systems for electric vehicles, improving their range and safety performance.

Smart Grid: Semiconductors are used in smart grids to optimize power distribution and consumption, enhance the reliability and efficiency of the power grid.

Energy conservation and emission reduction: By improving energy efficiency, semiconductor technology helps reduce overall energy consumption and carbon emissions.