Semiconductor: Types, Properties, Materials, Devices, & Use

A semiconductor is a type of material that falls between conductors (materials that allow easy flow of electricity) and insulators (materials that prevent the flow of electricity).

Semiconductors have unique properties that make them useful for controlling the flow of electric current. The key property of semiconductors is their ability to conduct electricity under certain conditions but not as easily as conductors. This means that they can be used to regulate and manipulate the flow of electrons.

The behavior of semiconductors is influenced by the presence of impurities, a process known as “doping.” By adding specific impurities to the semiconductor material, the conductivity can be modified. There are two types of doping: adding impurities with extra electrons (n-type doping) or adding impurities with fewer electrons (p-type doping).

When a semiconductor is doped, it creates an excess of either negatively charged particles (electrons) or positively charged particles (holes) within the material. These charged particles are called “carriers” and are responsible for the flow of electric current.

Semiconductors are the foundation of modern electronics. They are used to create components like diodes, transistors, and integrated circuits (ICs). These components are vital for various devices, such as computers, smartphones, televisions, and many other electronic systems.

Semiconductors have revolutionized the world of technology, enabling the development of smaller, faster, and more efficient devices.

The post also includes:

• Types of semiconductor
• Basic properties of semiconductors
• Difference between conductors, insulators, and semiconductors
• Semiconductor Materials
• Semiconductor Devices
• Semiconductor Fabrication Processes
• Use of Semiconductors
• Why are semiconductors used in electronics?
• FAQs

Types of semiconductor

There are two main types of semiconductors based on the charge carriers they possess:

1. Intrinsic Semiconductors:

• Intrinsic semiconductors are pure semiconductor materials with an equal number of electrons and holes.
• Examples of intrinsic semiconductors include pure silicon (Si) and pure germanium (Ge).
• Intrinsic semiconductors have a natural ability to conduct electricity when provided with sufficient energy.

2. Extrinsic Semiconductors:

• Extrinsic semiconductors are semiconductor materials that have been intentionally doped with impurities.
• Doping involves adding small amounts of impurity atoms to modify the electrical properties of the semiconductor.
• Extrinsic semiconductors are classified into two types based on the type of impurity added:

a) N-type Semiconductors:

• N-type semiconductors are doped with impurities that provide extra electrons.
• The most common dopants for n-type semiconductors include phosphorus (P), arsenic (As), and antimony (Sb).
• These extra electrons become the majority charge carriers in the material, resulting in high electron conductivity.

b) P-type Semiconductors:

• P-type semiconductors are doped with impurities that create an excess of “holes,” which are vacancies in the electron structure.
• The most common dopants for p-type semiconductors include boron (B), gallium (Ga), and indium (In).
• Holes become the majority charge carriers in the material, and they contribute to the conductivity of p-type semiconductors.

Basic properties of semiconductors

Here are the basic properties of semiconductors:

1. Conductivity: Semiconductors have moderate conductivity, which means they can conduct electricity, but not as well as conductors like copper or aluminum. They are not as “free” for the flow of electrons as conductors but are not as restrictive as insulators.

2. Band Gap: Semiconductors have a property called a “band gap.” It is the energy difference between the valence band (which contains electrons) and the conduction band (where electrons can move freely). The band gap determines whether a material is a conductor, insulator, or semiconductor.

3. Electrons and Holes: In semiconductors, when some electrons gain enough energy, they move from the valence band to the conduction band, leaving behind “holes” in the valence band. Both the electrons in the conduction band and the holes in the valence band can carry electric current.

4. Doping: Doping is the process of intentionally adding impurities to a semiconductor. It modifies its electrical properties. Doping with impurities that have extra electrons creates an “n-type” semiconductor while doping with impurities that have fewer electrons creates a “p-type” semiconductor.

5. Carrier Mobility: Carrier mobility refers to how easily and quickly the charge carriers (electrons or holes) can move through the semiconductor when subjected to an electric field. Higher carrier mobility allows for better conductivity and faster electronic devices.

6. Temperature Sensitivity: Semiconductors are sensitive to temperature changes. As the temperature increases, more electrons gain sufficient energy to move to the conduction band, increasing conductivity. However, at very high temperatures, the material’s properties may change, affecting its performance.

7. Light Sensitivity: Some semiconductors are sensitive to light and can generate an electric current when exposed to photons (particles of light). This property is used in devices such as solar cells and light sensors.

Difference between conductors, insulators, and semiconductors

Here are some differences between conductors, insulators, and semiconductors:

Conductors:

• Conductors are materials that allow the easy flow of electric current.
• They have a high conductivity and low resistance to the flow of electrons.
• Examples of conductors include metals like copper, aluminum, and silver.
• Conductors have a small or negligible energy band gap, which allows electrons to move freely.

Insulators:

• Insulators are materials that prevent or hinder the flow of electric current.
• They have a high resistance to the flow of electrons and very low conductivity.
• Examples of insulators include rubber, plastic, glass, and wood.
• Insulators have a large energy band gap, which makes it difficult for electrons to move.

Semiconductors:

• Semiconductors are materials that have electrical conductivity between conductors and insulators.
• They have moderate conductivity, which can be controlled and modified.
• Examples of semiconductors include silicon, germanium, and gallium arsenide.
• Semiconductors have a moderate energy band gap, which allows them to conduct under specific conditions.

Semiconductor Materials

Semiconductor materials are the specific types of materials that are used to make semiconductors. These materials have unique properties that allow them to conduct electricity under certain conditions, making them essential for electronic devices. Here are some commonly used semiconductor materials:

1. Silicon:

• Silicon is the most widely used semiconductor material.
• It is abundant in nature and relatively easy to purify and process.
• Silicon is the main material used in manufacturing electronic components such as transistors and integrated circuits (ICs).
• It has a moderate energy band gap, which enables it to conduct electricity when appropriately doped.

2. Germanium:

• Germanium is another semiconductor material that was widely used in early electronic devices.
• It has similar properties to silicon but is less commonly used today.
• Germanium has a smaller energy band gap compared to silicon, making it more conductive at room temperature.
• It is still used in some specialized applications like infrared detectors.

3. Gallium Arsenide:

• Gallium arsenide (GaAs) is a compound semiconductor material.
• It has higher electron mobility and can operate at higher frequencies than silicon.
• GaAs are often used in high-speed electronic devices like microwave circuits, optical detectors, and solar cells.
• It is especially valued in applications where high performance and high-frequency operation are crucial.

4. Other Compound Semiconductors:

• Besides gallium arsenide, there are various other compound semiconductors used for specific applications.
• Examples include indium phosphide (InP), gallium nitride (GaN), and gallium phosphide (GaP).
• Compound semiconductors are composed of two or more elements, offering unique electrical and optical properties.

List of some other materials:

• Silicon (Si)
• Germanium (Ge)
• Gallium Arsenide (GaAs)
• Indium Phosphide (InP)
• Gallium Nitride (GaN)
• Gallium Phosphide (GaP)
• Silicon Carbide (SiC)
• Cadmium Sulfide (CdS)
• Zinc Oxide (ZnO)
• Lead Sulfide (PbS)
• Cadmium Telluride (CdTe)
• Indium Antimonide (InSb)
• Indium Arsenide (InAs)
• Mercury Cadmium Telluride (HgCdTe)
• Gallium Nitride (GaN)
• Aluminum Gallium Arsenide (AlGaAs)
• Silicon Germanium (SiGe)

Doping and Carrier Concentration

Let’s dive into doping and carrier concentration in simple terms:

1. Doping:

• Doping is the intentional introduction of impurities into a semiconductor material to alter its electrical properties.
• Impurities are atoms of different elements that are added to the semiconductor crystal during the manufacturing process.
• Doping is done to increase the conductivity or control the behavior of the semiconductor.
• Two types of doping are commonly used: n-type doping and p-type doping.

2. N-type Doping:

• N-type doping involves adding impurities that have extra electrons compared to the atoms of the semiconductor material.
• The impurity atoms with extra electrons are called donor atoms.
• When donor atoms are added to the semiconductor crystal, they provide additional electrons that become the majority carriers in the material.
• These extra electrons contribute to higher conductivity in the n-type semiconductor.

3. P-type Doping:

• P-type doping involves adding impurities that have fewer electrons compared to the atoms of the semiconductor material.
• The impurity atoms with fewer electrons are called acceptor atoms.
• When acceptor atoms are added to the semiconductor crystal, they create “holes” in the crystal lattice structure.
• These holes act as mobile positive charge carriers and become the majority carriers in the p-type semiconductor.
• The movement of holes contributes to the conductivity of the p-type semiconductor.

4. Carrier Concentration:

• Carrier concentration refers to the abundance of charge carriers (electrons or holes) in a semiconductor material.
• The concentration of carriers is influenced by the type and level of doping.
• In an n-type semiconductor, the majority of carriers are electrons, and the carrier concentration refers to the number of extra electrons.
• In a p-type semiconductor, the majority of carriers are holes, and the carrier concentration refers to the number of available holes.
• The concentration of carriers determines the conductivity and other electrical properties of the semiconductor.

Semiconductor Devices

Semiconductor devices are electronic components made from semiconductor materials that perform specific functions in electronic circuits. They are the building blocks of modern electronics. Here are some commonly used semiconductor devices explained in simple terms:

1. Diodes:

• Diodes are like one-way valves for electricity.
• They allow current to flow in one direction while blocking it in the opposite direction.
• Diodes are used in various applications such as rectification (converting AC to DC), voltage regulation, and signal demodulation.

2. Transistors:

• Transistors are tiny electronic switches or amplifiers.
• They can control the flow of current between two terminals based on a small input signal.
• Transistors come in different types: bipolar junction transistors (BJTs) and field-effect transistors (FETs).
• They are used in amplifiers, digital logic circuits, power regulators, and many other applications.

3. Integrated Circuits (ICs):

• Integrated circuits, also known as chips or microchips, are complete electronic circuits miniaturized onto a small silicon chip.
• They can contain millions or even billions of transistors and other components.
• ICs are used in a wide range of electronic devices, from computers and smartphones to televisions and medical equipment.

4. Sensors:

• Sensors are devices that detect and convert physical quantities or environmental conditions into electrical signals.
• Examples include temperature sensors, light sensors, pressure sensors, and motion sensors.
• Sensors are used in various applications like automotive systems, smartphones, environmental monitoring, and industrial control systems.

5. Light-Emitting Diodes (LEDs):

• LEDs are semiconductor devices that emit light when an electric current passes through them.
• They are used for lighting applications, displays (such as in TVs and smartphones), and indicators in electronic devices.
• LEDs offer energy efficiency, long life, and the ability to produce a wide range of colors.

6. Solar Cells:

• Solar cells, also known as photovoltaic cells, convert sunlight into electrical energy.
• They are made from semiconductor materials that generate an electric current when exposed to photons (particles of light).
• Solar cells are used in solar panels to generate renewable energy.

Semiconductor Fabrication Processes

Semiconductor fabrication processes, also known as semiconductor manufacturing or chip fabrication, involve a series of steps to create integrated circuits (ICs) and other semiconductor devices.

1. Wafer Preparation:

• The process begins with the preparation of a silicon wafer, which serves as the substrate for the semiconductor device.
• The wafer is usually made from high-purity crystalline silicon and undergoes cleaning and polishing to ensure a smooth and defect-free surface.

2. Photolithography:

• Photolithography is a key process in semiconductor manufacturing.
• A layer of photosensitive material, called a photoresist, is deposited on the wafer.
• A photomask, containing a pattern of the desired circuit design, is then aligned and exposed onto the photoresist-coated wafer using ultraviolet light.
• The exposed areas of the photoresist become either soluble (positive resist) or insoluble (negative resist) depending on the type of resist used.

3. Etching:

• Etching is used to selectively remove material from the wafer.
• The wafer is typically etched using either wet etching or dry etching techniques.
• Wet etching involves immersing the wafer in a chemical solution that selectively removes the exposed material.
• Dry etching uses plasma or reactive gases to remove the exposed material.
• Etching helps define the patterned features on the wafer according to the desired circuit design.

4. Deposition:

• Deposition processes are used to add or deposit various thin films of materials onto the wafer.
• Two common deposition techniques are physical vapor deposition (PVD) and chemical vapor deposition (CVD).
• PVD involves the evaporation or sputtering of materials in a vacuum chamber, which then condenses onto the wafer’s surface.
• CVD involves the introduction of precursor gases that react to form a solid material on the wafer’s surface.
• Deposition is used to create conductive, insulating, and other functional layers required for the circuitry.

5. Thermal Processes:

• Thermal processes, such as annealing and oxidation, are performed to modify the properties of deposited films and create desired electrical characteristics.
• Annealing involves heating the wafer to enhance the crystalline structure and repair defects in the semiconductor material.
• Oxidation is used to grow a thin layer of silicon dioxide (SiO2) on the wafer’s surface, which acts as an insulating layer or protective barrier.

6. Metallization:

• Metallization involves depositing metal layers, typically aluminum or copper, onto the wafer’s surface to create interconnections between different components of the circuit.
• Metal layers are patterned using additional photolithography and etching steps to create the desired interconnect structure.

7. Testing and Packaging:

• After the fabrication processes, the individual chips on the wafer are tested for functionality and quality.
• Good chips are separated from the wafer and undergo packaging, where they are placed into protective casings and connected to external pins or leads.
• Packaging ensures electrical connections, and protection from environmental factors, and facilitates integration into electronic devices.

Use of Semiconductors

Semiconductors have numerous applications across various industries. Here are some common uses of semiconductors:

1. Electronics and Computing:

• Semiconductors are the foundation of modern electronics and computing devices.
• They are used in computers, smartphones, tablets, televisions, and other consumer electronics.
• Semiconductors enable the processing, storage, and transmission of information in these devices.

2. Integrated Circuits (ICs):

• Integrated circuits, or microchips, are made from semiconductors.
• They contain millions or billions of transistors and other components on a small chip.
• ICs are used in almost all electronic devices to perform functions such as data processing, memory storage, and signal amplification.

3. Communications:

• Semiconductors play a vital role in communication systems.
• They are used in wireless devices like smartphones, routers, and satellite communication systems.
• Semiconductors enable the transmission and reception of signals in various communication technologies such as Wi-Fi, Bluetooth, and cellular networks.

4. Optoelectronics:

• Semiconductors are used in optoelectronic devices that interact with light.
• Light-emitting diodes (LEDs) are semiconductors that emit light when an electric current passes through them.
• Lasers, photodetectors, and solar cells are other examples of optoelectronic devices made from semiconductors.

5. Renewable Energy:

• Semiconductors are crucial for renewable energy generation and storage.
• Solar cells, made from semiconductors, convert sunlight into electricity.
• Semiconductors also play a role in energy storage devices like rechargeable batteries.

6. Automotive Electronics:

• Semiconductors are extensively used in automotive electronics.
• They enable various features like engine control, safety systems, entertainment systems, and navigation systems in vehicles.
• Semiconductors also contribute to advanced driver-assistance systems (ADAS) and autonomous driving technologies.

7. Industrial Applications:

• Semiconductors find applications in industrial systems and automation.
• They are used in control systems, robotics, sensors, and monitoring devices in manufacturing and process industries.

8. Medical Devices:

• Semiconductors are used in medical devices for diagnostics, imaging, and treatment.
• They contribute to devices such as ultrasound machines, MRI scanners, pacemakers, and blood glucose monitors.

Why are semiconductors used in electronics?

Semiconductors are used in electronics for several key reasons:

1. Control: Semiconductors can control the flow of electric current, acting as switches, amplifiers, and regulators.

2. Versatility: Semiconductors have diverse electrical properties that can be customized for specific needs.

3. Miniaturization: Semiconductors enable the creation of small and powerful electronic devices.

4. Integrated Circuits: Semiconductor-based chips integrate multiple functions into a single package.

5. Energy Efficiency: Semiconductors reduce energy consumption in electronic devices.

6. Signal Processing: Semiconductors process and manipulate electrical signals.

7. Optoelectronics: Semiconductors enable the production of light-emitting diodes (LEDs) and laser diodes.

8. Sensing and Detection: Semiconductors are used in sensors that convert physical phenomena into electrical signals.

FAQs

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Sources:

1. Semiconductor – Wikipedia – https://en.wikipedia.org/wiki/Semiconductor
2. What Is a Semiconductor and How Is It Used? – https://www.investopedia.com/terms/s/semiconductor.asp
3. Semiconductor manufacturing process – https://www.hitachi-hightech.com/global/en/knowledge/semiconductor/room/manufacturing/process.html
4. Semiconductor Materials – https://irds.ieee.org/topics/semiconductor-materials

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