What makes silicon a semiconductor material

Semiconductor physics / semiconductor technology

The specific resistance of a semiconductor is several powers of ten higher than that of metallic conductors. The conductivity is significantly lower than that of metals or alloys. The electrical conductivity of semiconductors is between that of metals and insulators. However, it is heavily dependent on

  • mechanical force (influences the mobility of the charge carriers)
  • Temperature (number and mobility of the charge carriers)
  • Exposure (number of charge carriers)
  • Foreign matter added (number and type of load carriers)

The conductivity of the semiconductors is low at room temperature. If you add energy in the form of heat, light, voltage, or magnetic energy, the conductivity changes. The sensitivity of semiconductors to pressure, temperature and light makes them suitable sensors.

Semiconductor materials

Semiconductor materials have a crystal structure. The atoms are in a given place. They are arranged according to a certain scheme. The property of the semiconductor depends on the crystal structure. These crystals must have a very high degree of purity. They can only consist of one element. Impurities in the form of other atoms change the properties of the semiconductor material.
The best-known semiconductor material is silicon (Si). It is very common in nature. For example in sand, quartz and stones. Germanium (Ge) is also quite well known. But it doesn't occur that often and is not used that often.

Chemical classification of semiconductors

Elementary semiconductors
  • Silicon (Si)
  • Germanium (Ge)
  • Boron (B)
  • Selenium (Se)
  • Tellurium (Te)
Compound semiconductors
  • Gallium arsenide (GaAs)
  • Indium phosphide (InP)
  • Indium antimonide (InSb)
  • Indium arsenide (InAs)
  • Gallium antimonide (GaSb)
  • Gallium nitride (GaN)
  • Gallium phosphide (GaP)
  • Cadmium sulfide (CdS)
  • Zinc oxide (ZnO)
  • Zinc sulfide (ZnS)
  • Silicon carbide (SiC)
Organic semiconductors
  • Phthalocyanine
  • Tetracene
  • Pentacene
  • Polyvinyl carbazole
  • TCNQ

Classification of semiconductors according to their electrical conductivity

Applications of semiconductor materials

Application / componentsSemiconductor materials
Diode, transistor, integrated circuitGe, Si, GaAs
Strain gaugesGe, Si
NTC resistanceSi, Ge, GaAs
LED, displaySiC, GaP, GaAs, InAs, InSb
Laser diodeGaAs, InAs, InSb
Photo element, solar cell, LDR Si, GaAs, CdS, CdSe
Hall generator, field plateInSb, InAs

Intrinsic conductivity

The electrical conductivity of a material depends on the number of free electrons on the outer shell of an atom (Bohr's atomic model).
The electrons in the semiconductors are usually used by the crystal formation. The crystal formation cannot simply be reversed. A semiconductor crystal is therefore a non-conductor.
Free charge carriers (electrons) are only created in the following exceptional cases.

  • Due to contamination of the semiconductor.
  • Light and heat cause the atoms to vibrate and release charge carriers.
  • The atoms on the material surface have no neighboring atoms and therefore have free electrons.

Intrinsic conductivity and temperature

By supplying heat or irradiation with light, undoped semiconductors can also generate free charge carriers. As the temperature rises, the number of square electron-hole pairs increases. This results in limits for the maximum operating temperature in electronic devices.

  • Germanium (90 ... 100 ° C)
  • Silicon (150 ... 200 ° C)
  • Gallium arsenide (300..350 ° C)

The intrinsic conduction in chemically pure semiconductor crystals is undesirable because of the strong temperature dependence and makes the technical use of semiconductors almost unusable. Therefore, semiconductor crystals are deliberately contaminated with foreign atoms. This process is called doping. There is either an excess of electrons or a lack of electrons. This makes the semiconductor more usable. By bringing together different semiconductor layers, semiconductor components are created. For example the diode and the transistor.

Inner photoelectric effect

Semiconductor materials have an intrinsic conductivity that is increased by heating and exposure to light. Energy in the form of heat and light increases conductivity. The electrons are torn from their bonds. The current flow increases. When light is irradiated, the light particles, called photons, hit the semiconductor material and break the crystal bonds. The electrons are literally blasted out. This increases the number of electrons and holes, i.e. the number of free charge carriers. This process is called the internal photoelectric effect.
Since the electrical properties of all semiconductor components are influenced by light, opaque housings are used. Except for photo elements such as photo resistors, photo diodes, photo transistors and solar cells. There the light is used specifically to change the electrical properties. In the solar cell, light is even used to generate electricity.

Overview: semiconductor physics

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