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Semiconductor

Semiconductor is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Semiconductor rather than just read about it. In short: A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities ("doping") to its crystal structure.

Semiconductor — main illustration
Semiconductor — illustration

Key takeaways

  • Semiconductor belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Semiconductor to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Semiconductor from memory before moving on to harder problems.

Reference excerpt

A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities ("doping") to its crystal structure. When two regions with different doping levels are present in the same crystal, they form a semiconductor junction. The term "semiconductors" is sometimes used to refer to semiconductor devices such as microchips and computer processors, which work using the physical properties of semiconductors. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits. Semiconductor devices can display a range of different useful properties, such as passing current more easily in one direction than the other, showing variable resistance, and having sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping and by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion. The term semiconductor is also used to describe materials used in high capacity, medium- to high-voltage cables as part of their insulation, and these materials are often plastic XLPE (cross-linked polyethylene) with carbon black. The conductivity of silicon can be increased by adding a small amount (of the order of 1 in 108) of pentavalent (antimony, phosphorus, or arsenic) or trivalent (boron, gallium, indium) atoms. This process is known as doping, and the resulting semiconductors are known as doped or extrinsic semiconductors. Apart from doping, the conductivity of a semiconductor can be improved by increasing its temperature. This is contrary to the behavior of a metal, in which conductivity decreases with an increase in temperature. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of charge carriers in a crystal lattice. Doping greatly increases the number of charge carriers within the crystal. When a semiconductor is doped by Group V elements, they will behave like donors creating free electrons, known as "n-type" doping. When a semiconductor is doped by Group III elements, they will behave like acceptors creating free holes, known as "p-type" doping. The semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor device crystal can have many p- and n-type regions; the p–n junctions between these regions are responsible for the useful electronic behavior. Using a hot-point probe, one can determine quickly whether a semiconductor sample is p- or n-type. A few of the properties of semiconductor materials were observed throughout the mid-19th and first decades of the 20th century. The first practical application of semiconductors in electronics was the 1904 development of the cat's-whisker detector, a primitive semiconductor diode used in early radio receivers. Developments in quantum physics led in turn to the invention of the transistor in 1947 and the integrated circuit in 1958.

Properties

Variable electrical conductivity Semiconductors in their natural state are poor conductors because a current requires flow of electrons, and semiconductors have their valence bands filled, preventing the entire flow of new electrons. Several developed techniques allow semiconducting materials to behave like conducting materials, such as doping or gating. These modifications have two outcomes: n-type and p-type. These refer to the excess or shortage of electrons, respectively. A balanced number of electrons would cause a current to flow throughout the material.

Homojunctions Homojunctions occur when two differently doped semiconducting materials are joined. For example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials. The n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until an equilibrium is reached by a process called recombination, which causes the migrating electrons from the n-type to come in contact with the migrating holes from the p-type. The result of this process is a narrow strip of immobile ions, which causes an electric field across the junction.

Excited electrons A difference in the electric potential on a semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion. Whenever thermal equilibrium is disturbed in a semiconducting material, the number of holes and electrons changes. Such disruptions can occur as a result of a temperature difference or photons, which can enter the system and create electrons and holes. The processes that create or annihilate electrons and holes are called generation and recombination, respectively.

Light emission In certain semiconductors, excited electrons can relax by emitting light instead of producing heat. Controlling the semiconductor composition and electrical current allows for the manipulation of the emitted light's properties. These semiconductors are used in the construction of light-emitting diodes and fluorescent quantum dots.

High thermal conductivity Semiconductors with high thermal conductivity can be used for heat dissipation and improving thermal management of electronics. They play a crucial role in electric vehicles, high-brightness LEDs and power modules, among other applications.

Thermal energy conversion Semiconductors have large thermoelectric power factors making them useful in thermoelectric generators, as well as high thermoelectric figures of merit making them useful in thermoelectric coolers.

Materials

A large number of elements and compounds have semiconducting properties, including:

… excerpt ends here. Continue reading the full article.

Illustrations

Semiconductor: Silicon crystals are the most common semiconducting materials used in microelectronics and photovoltaics.
Silicon crystals are the most common semiconducting materials used in microelectronics and photovoltaics.
Semiconductor: Filling of the electronic states in various types of materials at equilibrium. Here, height is energy while width is the density of available states for a certain energy in the material listed. The shade follows the Fermi–Dirac distribution (black: all states filled, white: no state filled). In metals and semimetals the Fermi level EF lies inside at least one band. In insulators and semiconductors the Fermi level is inside a band gap; however, in semiconductors the bands are near enough to the Fermi level to be thermally populated with electrons or holes. "intrin." indicates intrinsic semiconductors. edit
Filling of the electronic states in various types of materials at equilibrium. Here, height is energy while width is the density of available states for a certain energy in the material listed. The shade follows the Fermi–Dirac distribution (black: all states filled, white: no state filled). In metals and semimetals the Fermi level EF lies inside at least one band. In insulators and semiconductors the Fermi level is inside a band gap; however, in semiconductors the bands are near enough to the Fermi level to be thermally populated with electrons or holes. "intrin." indicates intrinsic semiconductors. edit
Semiconductor: Doping of a pure silicon array. Silicon based intrinsic semiconductor becomes extrinsic when impurities such as Boron and Antimony are introduced.
Doping of a pure silicon array. Silicon based intrinsic semiconductor becomes extrinsic when impurities such as Boron and Antimony are introduced.
Semiconductor: Karl Ferdinand Braun developed the crystal detector, the first semiconductor device, in 1874.
Karl Ferdinand Braun developed the crystal detector, the first semiconductor device, in 1874.
Semiconductor: John Bardeen, William Shockley and Walter Brattain developed the bipolar point-contact transistor in 1947.
John Bardeen, William Shockley and Walter Brattain developed the bipolar point-contact transistor in 1947.

Worked examples

Example 1 — a first encounter with Semiconductor

Start with the simplest possible case. Write down what Semiconductor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Semiconductor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Semiconductor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Semiconductor

In research
Semiconductor appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Semiconductor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Semiconductor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Semiconductors, so understanding it makes those chapters shorter.
In everyday life
Look for Semiconductor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Semiconductor in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Semiconductor means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Semiconductor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Semiconductor in simple terms?

A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities ("doping") to its crystal structure.

Why does Semiconductor matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Semiconductor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Semiconductor.

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