Semiconductor: An Educational Resource

semiconductor, electronics, materials, physics

An educational resource on semiconductors, including their properties, materials, preparation, and physics.

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Introduction to Semiconductors

A semiconductor is a material with electrical conductivity between that of a conductor (like copper) and an insulator (like glass). This unique property makes semiconductors essential components in modern electronics.

Semiconductor: A material with electrical conductivity ranging between conductors and insulators. Its conductivity can be manipulated by external factors like temperature, light, and the introduction of impurities.

Unlike conductors that readily allow electric current to flow and insulators that strongly resist it, semiconductors can be controlled to either conduct or insulate under different conditions. This controllability is the key to their usefulness.

Key Characteristics of Semiconductors:

• Intermediate Conductivity: Their ability to conduct electricity is between conductors and insulators.
• Modifiable Conductivity: Their conductivity can be significantly altered by:
  • Doping: Introducing specific impurities into their crystal structure.
  • Temperature: Increasing temperature generally increases conductivity in semiconductors, unlike metals.
  • Light: Exposure to light can generate charge carriers, increasing conductivity.
  • Electric Fields: Applying electric fields can modulate conductivity.

These characteristics enable semiconductors to perform a wide range of functions in electronic devices, including:

• Switching: Turning electrical circuits on and off (like transistors).
• Amplification: Increasing the strength of electrical signals (also transistors).
• Rectification: Converting alternating current (AC) to direct current (DC) (like diodes).
• Energy Conversion: Converting light to electricity (like solar cells) or electricity to light (like LEDs).

Common Semiconductor Materials:

Several materials exhibit semiconducting properties. Some prominent examples include:

• Silicon (Si): The most widely used semiconductor material in the electronics industry due to its abundance, cost-effectiveness, and suitable electrical properties. It forms the basis of most integrated circuits and computer chips.
• Germanium (Ge): Historically important in early transistors but now less common than silicon due to its temperature sensitivity and other limitations.
• Gallium Arsenide (GaAs): A compound semiconductor known for its higher electron mobility compared to silicon. It is used in specialized applications like:
  • Laser diodes: Used in CD/DVD players, barcode scanners, and fiber optic communication.
  • Solar cells: Especially high-efficiency solar cells for space and terrestrial applications.
  • Microwave-frequency integrated circuits: Used in high-speed communication and radar systems.
• Metalloids: Elements located near the “metalloid staircase” on the periodic table (e.g., Boron, Antimony, Tellurium) can also exhibit semiconducting properties.

Metalloid Staircase: A diagonal line on the periodic table separating metals from nonmetals. Elements near this staircase often exhibit properties intermediate between metals and nonmetals, including semiconducting behavior.

Semiconductor Junctions: The Building Blocks of Electronics

A crucial concept in semiconductor technology is the semiconductor junction. This is formed when two regions of a semiconductor crystal are doped differently, creating distinct electrical properties within the same material.

Semiconductor Junction: The interface created when two regions of a semiconductor material are doped with different types of impurities (e.g., p-type and n-type). These junctions are fundamental to the operation of diodes and transistors.

The behavior of charge carriers (electrons and holes) at these junctions is the foundation for many essential electronic components:

• Diodes: Allow current to flow primarily in one direction, enabling rectification and switching functions.
• Transistors: Act as electronic switches and amplifiers, controlling the flow of current based on an input signal.
• Integrated Circuits (ICs): Complex circuits built by combining millions or billions of transistors and other components on a single semiconductor chip, enabling complex electronic functions in computers, smartphones, and other devices.

Properties of Semiconductors

Semiconductors exhibit a range of properties that make them exceptionally versatile for electronic applications.

Variable Electrical Conductivity

In their pure, intrinsic state, semiconductors are not very conductive. This is because their electrons are tightly bound in chemical bonds, and there are few free charge carriers to conduct electricity.

Intrinsic Semiconductor: A pure semiconductor material with no dopants added. Its conductivity is primarily determined by its inherent electronic properties.

However, the conductivity of semiconductors can be dramatically changed through doping and gating.

Doping: Tailoring Conductivity

Doping is the process of intentionally introducing impurities into a semiconductor crystal to modify its electrical conductivity. These impurities, called dopants, alter the number of charge carriers available within the material.

Doping: The intentional introduction of impurities into an intrinsic semiconductor to modify its electrical conductivity. Dopants can be either donors (n-type doping) or acceptors (p-type doping).

There are two main types of doping:

• n-type doping: Introducing impurities that have more valence electrons than the semiconductor atoms (typically Group V elements like phosphorus, arsenic, or antimony into silicon, which is Group IV). These impurities donate extra electrons to the semiconductor, increasing the number of free electrons (negative charge carriers). Hence, “n-type” for negative.
• p-type doping: Introducing impurities that have fewer valence electrons than the semiconductor atoms (typically Group III elements like boron, gallium, or indium into silicon). These impurities create “holes” (absence of electrons) in the semiconductor’s electron structure. These holes can be considered positive charge carriers. Hence, “p-type” for positive.

n-type Semiconductor: A semiconductor doped with donor impurities, resulting in an excess of free electrons as majority charge carriers.

p-type Semiconductor: A semiconductor doped with acceptor impurities, resulting in an excess of holes as majority charge carriers.

Example of Doping Silicon:

• n-type: Adding phosphorus (Group V) to silicon (Group IV). Phosphorus has 5 valence electrons. When it replaces a silicon atom, 4 electrons form bonds with neighboring silicon atoms, and the 5th electron becomes a free electron, increasing conductivity and creating an n-type semiconductor.
• p-type: Adding boron (Group III) to silicon (Group IV). Boron has 3 valence electrons. When it replaces a silicon atom, it can only form 3 bonds. This creates a “hole” (missing electron) that can move around and act as a positive charge carrier, creating a p-type semiconductor.

Gating: Electric Field Control

Gating refers to using an electric field to control the conductivity of a semiconductor. This is the principle behind field-effect transistors (FETs). By applying a voltage to a “gate” electrode, the electric field can attract or repel charge carriers in the semiconductor channel beneath the gate, effectively controlling the current flow.

Homojunctions

A homojunction is formed when two regions of the same semiconductor material are doped differently, typically creating a junction between a p-type region and an n-type region (a p-n junction).

Homojunction: A junction formed between two differently doped regions of the same semiconductor material. A common example is a p-n junction.

Formation of a p-n junction:

1. Diffusion of Charge Carriers: At the junction, there is a high concentration of electrons in the n-type region and a high concentration of holes in the p-type region. Electrons from the n-type region diffuse across the junction into the p-type region, and holes from the p-type region diffuse into the n-type region.
2. Recombination: When electrons and holes meet at the junction, they recombine. This means an electron fills a hole, effectively eliminating both charge carriers in that region.
3. Depletion Region: The recombination process depletes the area around the junction of mobile charge carriers (electrons and holes). This region is called the depletion region or space charge region. Within this region, immobile ionized dopant atoms are left behind (positive ions in the n-side and negative ions in the p-side).
4. Electric Field: The immobile ions in the depletion region create an electric field across the junction, pointing from the positive n-side ions to the negative p-side ions. This electric field opposes further diffusion of charge carriers and establishes an equilibrium.

The p-n junction is the fundamental building block of diodes and transistors. Its properties are crucial for rectification, switching, and amplification.

Excited Electrons

Semiconductors are sensitive to external stimuli like voltage, temperature, and light, which can disrupt their thermal equilibrium and excite electrons.

• Voltage: Applying a voltage across a semiconductor can inject or extract charge carriers, leading to non-equilibrium conditions and current flow.
• Temperature: Increasing temperature provides thermal energy that can excite electrons from the valence band to the conduction band, increasing the number of charge carriers and conductivity.
• Photons (Light): When light shines on a semiconductor, photons with sufficient energy can be absorbed, exciting electrons and creating electron-hole pairs. This is the basis of photodiodes and solar cells.

Electron-Hole Pair: Created when an electron is excited from the valence band to the conduction band, leaving behind a “hole” in the valence band. Both the electron and the hole can act as charge carriers.

Generation and Recombination

• Generation: Processes that create electron-hole pairs. This can be due to thermal energy, light absorption, or high-energy radiation.
• Recombination: Processes where electrons and holes meet and annihilate each other, returning electrons to lower energy levels. Energy released during recombination can be emitted as heat (phonons) or light (photons).

Generation (of charge carriers): The process of creating electron-hole pairs in a semiconductor, increasing the concentration of charge carriers.

Recombination (of charge carriers): The process of an electron and a hole annihilating each other, reducing the concentration of charge carriers.

Light Emission

In certain direct band gap semiconductors like gallium arsenide (GaAs) and gallium nitride (GaN), when excited electrons recombine, they can release energy in the form of light (photons) rather than just heat (phonons). This phenomenon is called luminescence.

Direct Band Gap Semiconductor: A semiconductor where the lowest energy level in the conduction band and the highest energy level in the valence band occur at the same momentum value. This allows for efficient radiative recombination (light emission).

By controlling the semiconductor material’s composition and the applied electrical current, the wavelength (color) and intensity of the emitted light can be precisely controlled. This property is exploited in:

• Light-Emitting Diodes (LEDs): Efficient light sources that emit light when current flows through them.
• Laser Diodes: Similar to LEDs but produce coherent and monochromatic (single-color) light.
• Fluorescent Quantum Dots: Nanometer-sized semiconductor crystals that emit light of specific colors when excited by UV light or electricity.

High Thermal Conductivity

Some semiconductors, particularly those based on diamond and silicon carbide (SiC), exhibit high thermal conductivity. This property is crucial for:

• Heat Dissipation: Efficiently removing heat generated by electronic devices, preventing overheating and improving performance and reliability.
• Thermal Management: Designing electronic systems that can operate at high power densities without thermal issues.

High thermal conductivity semiconductors are important in applications like:

• Electric Vehicles: Managing heat in high-power electronics for motors and power converters.
• High-Brightness LEDs: Dissipating heat generated in high-power LED lighting.
• Power Modules: Cooling high-power semiconductor devices in industrial and automotive applications.

Thermal Energy Conversion

Semiconductors can also be used for thermal energy conversion, meaning they can convert temperature differences into electrical energy (thermoelectric generation) or use electrical energy to create temperature differences (thermoelectric cooling).

• Thermoelectric Generators (TEGs): Utilize the Seebeck effect to generate electricity from a temperature gradient. Semiconductors with high thermoelectric power factor are essential for efficient TEGs.
• Thermoelectric Coolers (TECs) (Peltier Coolers): Utilize the Peltier effect to create a temperature difference when an electric current flows through a semiconductor junction. Semiconductors with a high thermoelectric figure of merit (ZT) are needed for effective TECs.

Seebeck Effect: The phenomenon where a temperature difference between two different electrical conductors or semiconductors creates a voltage difference between them.

Peltier Effect: The phenomenon where heat is either absorbed or released at the junction between two different conductors or semiconductors when an electric current flows through the junction.

Thermoelectric Power Factor: A measure of a material’s ability to generate voltage in response to a temperature difference.

Thermoelectric Figure of Merit (ZT): A dimensionless quantity that measures the efficiency of a thermoelectric material for energy conversion. Higher ZT values indicate better thermoelectric performance.

Materials Used in Semiconductors

A wide variety of materials exhibit semiconducting properties, categorized into different groups:

• Elemental Semiconductors: Pure elements from Group 14 of the periodic table.
  • Silicon (Si): Most important commercially.
  • Germanium (Ge): Historically significant.
• Binary Compounds: Compounds formed between two elements from different groups.
  • Group 13-15 Compounds: Gallium Arsenide (GaAs), Indium Phosphide (InP).
  • Group 12-16 Compounds: Cadmium Telluride (CdTe), Zinc Sulfide (ZnS).
  • Group 14-16 Compounds: Lead Sulfide (PbS), Tin Oxide (SnO2).
  • Group 14-14 Compounds: Silicon Carbide (SiC).
• Ternary Compounds, Oxides, and Alloys: More complex materials with three or more elements, including oxides (e.g., zinc oxide ZnO), and alloys (e.g., silicon-germanium SiGe).
• Organic Semiconductors: Semiconductors made from organic (carbon-based) compounds. These are used in flexible electronics and organic LEDs (OLEDs).
• Semiconducting Metal-Organic Frameworks (MOFs): Hybrid materials combining metal ions and organic linkers that exhibit semiconducting behavior.

Semiconducting materials can be crystalline, amorphous, or liquid.

• Crystalline Semiconductors: Atoms are arranged in a highly ordered, repeating lattice structure. Examples: Silicon, Germanium, Gallium Arsenide. Crystalline semiconductors generally have higher performance and are used in most high-performance electronics.
• Amorphous Semiconductors: Atoms are arranged in a disordered, non-crystalline structure. Examples: Hydrogenated amorphous silicon (a-Si:H), mixtures of arsenic, selenium, and tellurium. Amorphous semiconductors are often used in thin-film applications like solar cells and LCD displays because they can be deposited over large areas and are less sensitive to impurities and radiation damage.
• Liquid Semiconductors: Semiconductors in a liquid state, typically at high temperatures. These are less common in practical applications but are studied for their unique electronic properties.

Preparation of Semiconductor Materials

The fabrication of semiconductor devices, especially integrated circuits (ICs), requires extremely pure and structurally perfect semiconductor materials. Impurities and crystal defects can significantly degrade device performance.

Material Purity and Crystal Perfection

• Chemical Purity: Semiconductor materials for ICs must have extremely high chemical purity, often in the parts-per-trillion range. Even trace amounts of impurities can drastically alter electrical properties.
• Crystalline Perfection: The crystal structure must be highly perfect with minimal defects like dislocations, twins, and stacking faults. These defects can act as scattering centers for charge carriers, reducing mobility and device performance.

Crystal Growth

Large, single-crystal ingots of semiconductor materials are grown using techniques like the Czochralski method.

Czochralski Method: A crystal growth technique used to produce large, single-crystal ingots of semiconductors (like silicon). A seed crystal is dipped into molten semiconductor material and slowly pulled upwards while rotating, allowing a large single crystal to grow.

1. Melting: The semiconductor material (e.g., silicon) is melted in a crucible at high temperature.
2. Seeding: A small, precisely oriented seed crystal of the same material is dipped into the melt.
3. Pulling and Rotation: The seed crystal is slowly pulled upwards while being rotated. As the seed is pulled, molten material solidifies onto it, growing a large, cylindrical single crystal ingot.
4. Ingot Slicing: The grown ingot is then sliced into thin circular wafers.

Wafer: A thin slice of semiconductor material (typically silicon) used as the substrate for fabricating integrated circuits and other semiconductor devices.

Wafer Processing for Integrated Circuits

Creating integrated circuits on semiconductor wafers involves a series of complex processes:

1. Thermal Oxidation: Forming a layer of silicon dioxide (SiO₂) on the silicon wafer surface by heating it in an oxygen-rich atmosphere. SiO₂ acts as an insulator and is used as a gate insulator in transistors and as a field oxide to isolate different circuit components.
2. Photolithography: A process used to transfer circuit patterns onto the wafer.
   • Photoresist Coating: The wafer is coated with a light-sensitive material called photoresist.
   • Photomask: A photomask, containing the desired circuit pattern, is placed over the wafer.
   • UV Exposure: Ultraviolet (UV) light is shone through the photomask, exposing the photoresist according to the pattern.
   • Development: The exposed photoresist is developed, removing either the exposed or unexposed regions, depending on the type of photoresist (positive or negative). This leaves a patterned photoresist layer on the wafer.
3. Etching: Removing material from the wafer in the areas not protected by the patterned photoresist.
   • Plasma Etching: A common etching technique using plasma (ionized gas) in a low-pressure chamber. Reactive ions in the plasma chemically react with the exposed semiconductor material, etching it away anisotropically (directionally). Common etch gases include chlorofluorocarbons (Freons).
4. Diffusion (Doping): Introducing dopant atoms into specific regions of the wafer to create p-type and n-type regions and form p-n junctions.
   • High-Temperature Diffusion: Wafers are heated to high temperatures (e.g., 1100 °C) in a furnace, and dopant gases are introduced. Dopant atoms diffuse into the silicon, creating doped regions.
   • Ion Implantation: Dopant ions are accelerated to high energies and implanted into the wafer. This allows for precise control over dopant concentration and depth.

These processes are repeated multiple times, using different photomasks and dopants, to build up the complex multilayer structure of an integrated circuit with transistors, diodes, and interconnections on a single semiconductor chip.

Physics of Semiconductors

The behavior of semiconductors is fundamentally governed by quantum physics and solid-state physics principles.

Energy Bands and Electrical Conduction

The electrical conductivity of materials (conductors, semiconductors, and insulators) can be explained by their electronic band structure.

Electronic Band Structure: Describes the allowed energy levels that electrons can occupy in a solid material. It consists of energy bands separated by band gaps.

• Energy Bands: Ranges of allowed energy levels for electrons in a solid. These bands arise from the quantization of electron energies in the periodic potential of the crystal lattice.
• Valence Band: The highest energy band that is normally filled with electrons at low temperatures.
• Conduction Band: The energy band above the valence band. Electrons in the conduction band are free to move and contribute to electrical conductivity.
• Band Gap (Energy Gap): The energy range between the valence band and the conduction band where no electron energy levels are allowed.

Conduction in Different Materials:

• Conductors (Metals): Have overlapping valence and conduction bands or a partially filled conduction band. Many free electrons are readily available in the conduction band, allowing for high electrical conductivity.
• Insulators: Have a large band gap. The valence band is completely filled, and the conduction band is empty. A very large amount of energy is required to excite electrons from the valence band to the conduction band, resulting in very low conductivity.
• Semiconductors: Have a smaller band gap than insulators. At room temperature, some thermal energy is sufficient to excite a small number of electrons from the valence band to the conduction band. This creates a moderate number of charge carriers (electrons in the conduction band and holes in the valence band), resulting in intermediate conductivity.

Fermi Level:

Fermi Level: The highest energy level that electrons can occupy at absolute zero temperature (0 Kelvin). At non-zero temperatures, it represents the energy level with a 50% probability of being occupied by an electron.

The position of the Fermi level relative to the energy bands is crucial for determining the electrical properties of a material.

• In conductors, the Fermi level lies within the conduction band.
• In insulators, the Fermi level lies within the band gap, far from both the valence and conduction bands.
• In intrinsic semiconductors, the Fermi level is near the middle of the band gap.
• Doping shifts the Fermi level closer to the conduction band (n-type) or valence band (p-type), significantly increasing conductivity.

Charge Carriers (Electrons and Holes)

Electrical current in semiconductors is carried by two types of charge carriers:

• Electrons: Negatively charged particles in the conduction band.
• Holes: Positively charged quasiparticles in the valence band, representing the absence of an electron.

Both electrons in the conduction band and holes in the valence band can move and contribute to current flow when an electric field is applied.

Electron and Hole Mobility:

Mobility: A measure of how easily charge carriers (electrons or holes) move through a material in response to an electric field. Higher mobility means carriers can move faster for a given electric field, leading to higher conductivity.

Electrons and holes have different mobilities in a semiconductor material, influenced by factors like:

• Material Properties: Band structure, crystal lattice, effective mass of carriers.
• Temperature: Mobility generally decreases with increasing temperature due to increased scattering of carriers by lattice vibrations (phonons).
• Doping Concentration: High doping levels can also reduce mobility due to increased impurity scattering.

Carrier Generation and Recombination

Electron-hole pairs are constantly being generated and recombining in semiconductors.

• Thermal Generation: At any temperature above absolute zero, thermal energy can excite electrons across the band gap, creating electron-hole pairs. The rate of thermal generation increases with temperature.
• Optical Generation: Absorption of photons with energy greater than the band gap can also generate electron-hole pairs. This is the basis of photodetection in semiconductors.
• Recombination: Electrons in the conduction band can recombine with holes in the valence band, annihilating both carriers. Energy released during recombination can be emitted as heat (phonons) or light (photons).

Equilibrium and Steady State:

In thermal equilibrium, the rate of generation of electron-hole pairs is equal to the rate of recombination. The product of electron concentration (n) and hole concentration (p) is a constant at a given temperature, known as the intrinsic carrier concentration squared (n_i²).

Intrinsic Carrier Concentration (n_i): The concentration of electrons and holes in an intrinsic (undoped) semiconductor in thermal equilibrium. It is temperature-dependent and characteristic of the semiconductor material.

Doping shifts the equilibrium concentrations of electrons and holes. In n-type semiconductors, the electron concentration is much higher than the hole concentration (electrons are majority carriers, holes are minority carriers). In p-type semiconductors, holes are majority carriers and electrons are minority carriers.

Doping (Detailed Explanation)

Doping is a crucial technique for controlling the conductivity and electrical properties of semiconductors.

Types of Dopants:

• Donors (n-type dopants): Impurities that donate extra electrons to the conduction band. Examples in silicon: Phosphorus (P), Arsenic (As), Antimony (Sb). These are typically Group V elements.
• Acceptors (p-type dopants): Impurities that create holes in the valence band. Examples in silicon: Boron (B), Gallium (Ga), Indium (In). These are typically Group III elements.

Mechanism of Doping:

• Substitutional Doping: Dopant atoms replace semiconductor atoms in the crystal lattice. For example, when phosphorus (Group V) substitutes for silicon (Group IV), it has one extra valence electron that becomes loosely bound and easily ionized into the conduction band. When boron (Group III) substitutes for silicon, it creates a “hole” or vacant electron state in the valence band.
• Interstitial Doping: Dopant atoms are located in interstitial sites between the lattice atoms. This is less common than substitutional doping for most semiconductors.

Doping Concentration:

The amount of dopant added is carefully controlled to achieve the desired conductivity. Even a small amount of doping (parts per million or parts per billion) can significantly alter the conductivity of a semiconductor.

Doping Techniques:

• Diffusion: Heating the semiconductor wafer in an atmosphere containing dopant gases. Dopant atoms diffuse into the wafer at high temperatures.
• Ion Implantation: Accelerating dopant ions and implanting them into the semiconductor wafer. Provides precise control over dopant concentration and depth.

Amorphous Semiconductors

Amorphous semiconductors lack the long-range crystalline order of crystalline semiconductors. Examples include amorphous silicon (a-Si) and chalcogenide glasses (containing elements like selenium and tellurium).

Properties of Amorphous Semiconductors:

• Disordered Structure: Atoms are arranged randomly without a repeating lattice structure.
• Defect States: Amorphous semiconductors have a high density of defect states within the band gap due to the disorder. These defect states can trap charge carriers and affect conductivity.
• Lower Mobility: Charge carrier mobility is generally lower in amorphous semiconductors compared to crystalline semiconductors due to scattering by the disordered structure and defect states.
• Thin-Film Applications: Amorphous semiconductors are well-suited for thin-film applications like solar cells, LCD displays, and image sensors due to their ability to be deposited over large areas and their lower material cost.
• Hydrogenation of Amorphous Silicon (a-Si:H): Adding hydrogen to amorphous silicon passivates some of the defect states, improving its electronic properties and making it suitable for solar cells and thin-film transistors.

Early History of Semiconductors

The discovery and understanding of semiconductors evolved over centuries, starting with observations of unusual electrical phenomena in certain materials.

19th Century Observations:

• 1821 - Seebeck Effect (Thomas Johann Seebeck): Discovered that semiconductors show a stronger thermoelectric effect than metals.
• 1833 - Temperature Dependence of Resistance (Michael Faraday): Observed that the resistance of silver sulfide decreases with increasing temperature, unlike metals where resistance typically increases.
• 1835 - Rectification (Peter Munck af Rosenschöld): Observed rectification in metallic sulfides, though initially ignored.
• 1839 - Photovoltaic Effect (Alexandre Edmond Becquerel): Discovered the photovoltaic effect, observing voltage generation when light strikes a junction between a solid and liquid electrolyte.
• 1873 - Light Sensitivity of Selenium (Willoughby Smith): Noticed that selenium resistors exhibit decreasing resistance when exposed to light.
• 1874 - Rectification in Metallic Sulfides (Karl Ferdinand Braun): Systematically studied conduction and rectification in metallic sulfides, recognizing their potential for device applications.
• 1876 - Photovoltaic Effect in Selenium (William Grylls Adams and Richard Evans Day): Observed the photovoltaic effect in selenium in solid state.
• 1878 - Hall Effect (Edwin Herbert Hall): Demonstrated the deflection of charge carriers in a magnetic field, providing insights into the nature of charge carriers.

Early 20th Century: Development of Theory

• 1897 - Discovery of the Electron (J.J. Thomson): Led to theories of electron-based conduction in solids.
• 1904 - Cat’s-Whisker Detector: First practical application of semiconductors in electronics – a primitive semiconductor diode used in early radio receivers.
• 1910 - Term “Halbleiter” (Semiconductor) (Josef Weiss): Introduced the term “Halbleiter” (German for semiconductor) in his Ph.D. thesis.
• 1914 - Classification of Materials (Johan Koenigsberger): Classified materials as metals, insulators, and “variable conductors” (semiconductors).
• 1922 - Light Emission from Silicon Carbide (Oleg Losev): Observed light emission from silicon carbide under current injection, the principle of LEDs, but without practical application at the time.
• 1928 - Theory of Electron Movement in Lattices (Felix Bloch): Developed quantum mechanical theory describing electron behavior in crystal lattices (Bloch theory).
• 1930 - Impurity Conductivity (B. Gudden): Proposed that conductivity in semiconductors is due to trace impurities.
• 1931 - Band Theory of Conduction (Alan Herries Wilson): Established band theory and the concept of band gaps, providing a theoretical framework for semiconductor behavior.
• 1930s - Metal-Semiconductor Junction Theory (Walter H. Schottky and Nevill Francis Mott): Developed models for potential barriers and characteristics of metal-semiconductor junctions.
• 1938 - Theory of Copper-Oxide Rectifier (Boris Davydov): Developed a theory explaining the copper-oxide rectifier, identifying the p-n junction, minority carriers, and surface states.

Mid-20th Century: Transistor and Integrated Circuit Revolution

• 1940s - Silicon Wafer Introduction: Silicon wafers began to be used as the primary semiconductor material.
• 1941 - p-n Junction Observation (Russell Ohl): Observed the first p-n junction in silicon.
• 1947 - Point-Contact Transistor Invention (John Bardeen, Walter Houser Brattain, William Shockley at Bell Labs): Revolutionized electronics with the invention of the first transistor, a solid-state amplifier and switch.
• 1954 - Silicon Junction Transistor Fabrication (Morris Tanenbaum at Bell Labs): Fabricated the first silicon junction transistor, a more robust and manufacturable type of transistor.
• 1958 - Integrated Circuit Invention (Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor): Invented the integrated circuit, combining multiple transistors and components on a single semiconductor chip, leading to the miniaturization and mass production of electronics.

See Also

• Deathnium (Humorous term for silicon in science fiction)
• Semiconductor device fabrication
• Semiconductor industry
• Semiconductor characterization techniques
• Transistor count

References

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Further Reading

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