The family of semiconductors, including synthesized in laboratories, represents one of the most versatile classes of materials. This class has broad application in the industry. One of distinctive properties of semiconductors is that at low temperatures they behave as dielectrics, and at high — as conductors.
The most known semiconductor is silicon (Si). But, besides it, many natural semiconductor materials are known today: cuprite (Cu2O), zinc blende (ZnS), galenite (PbS), etc.
Characteristic and definition of semiconductors
In Mendeleyev's table of 25 chemical elements are nonmetals from which 13 elements have semiconductor properties. The main difference of semiconductors from other elements is that their conductivity significantly increases at temperature increase.
Other feature of the semiconductor is that its resistance falls under the influence of light. And the electric conductance of semiconductors changes at addition in structure of insignificant amount of impurity.
Semiconductors can be met among chemical compounds with various crystal structures. For example, such elements as silicon and selenium, or double connections like gallium arsenide.
Many organic compounds, for example polyacetylene (SN) n also can belong to semiconductor materials. Semiconductors can show magnetic (Cd1-xMnxTe) or ferroelectric properties (SbSI). At sufficient alloying some become superconductors (SrTiO3 and GeTe).
The semiconductor can be defined as material with an electrical resistance from 10-4 to 107 Ohms · m. Possibly and such definition: width of the forbidden zone of the semiconductor has to be from 0 to 3 ev.
Properties of semiconductors: impurity and own conductivity
Pure semiconductor materials have own conductivity. Such semiconductors are also called own, they contain equal number of holes and free electrons. Own conductivity of semiconductors increases when heating. At a constant temperature the quantity of the recombining electrons and holes remains invariable.
Availability of impurity in semiconductors has significant effect on their conductivity. It allows to increase quantity of free electrons at a small number of holes and vice versa. Impurity semiconductors have impurity conductivity.
Impurity which with ease give to the semiconductor electrons are called donorny. For example, phosphorus and bismuth can be Donorny impurity.
Impurity which connect electrons of the semiconductor and increase thereby in it quantity of holes, call acceptor. Acceptor impurity: pine forest, gallium, indy.
Characteristics of the semiconductor depend on defects of its crystal structure. It is the main reason for need of cultivation for artificial conditions of extremely clean crystals.
Parameters of conductivity of the semiconductor at the same time can be operated by addition of the alloying additives. Crystals of silicon are alloyed by phosphorus which in this case is a donor for creation of a crystal of silicon of n-type. For receiving a crystal with hole conductivity silicon add an acceptor to the semiconductor a pine forest.
Types of semiconductors: single-element and two-element connections
The most widespread single-element semiconductor is silicon. Together with a germaniye (Ge), silicon is considered a prototype of a wide class of the semiconductors having similar structures of a crystal.
Structure of crystals of Si and Ge same that at diamond and α-tin with quadruple coordination where each atom is surrounded by 4 next atoms. Crystals reckon with tetradrichesky communication as basic for the industry and play a key role in modern technology.
Properties and use of single-element semiconductors:
- Silicon – the semiconductor which is actively used in solar batteries, and in an amorphous form it is possible to use it in thin-film solar batteries. Also it is the most often used semiconductor in photo cells. It is simple in production and possesses good mechanical and electric and qualities.
- Diamond – the semiconductor having excellent thermal conductivity, excellent optical and mechanical characteristics, high durability.
- Germany is used in gamma spectroscopy, highly effective photo cells. The element was applied during creation of the first diodes and transistors. It needs less cleaning, than to silicon.
- Selenium – the semiconductor used in selenic rectifiers it has high radiation stability and ability to self-recovery.
Growth of an ionnost of elements changes properties of semiconductors and allows to form two-element connections:
- Arsenide of gallium (GaAs) – the second in frequency application after silicon the semiconductor, usually it is used as a substrate for other conductors, for example, in IK-setodiodakh, high-frequency chips and transistors, photo cells, laser diodes, detectors of nuclear treatment. However it is fragile, contains more impurity and is difficult in production.
- Sulfide of zinc (ZnS) – zinc salt of hydrosulphuric acid is used in lasers and as a phosphor.
- Sulfide of tin (SnS) – the semiconductor used in photo diodes and photoresistors.
Examples of semiconductors
Oxides are wonderful isolation centers. Examples of semiconductors of this type – copper oxide, nickel oxide, copper dioxide, cobalt oxide, europium oxide, iron oxide, zinc oxide.
The procedure of cultivation of semiconductors of this type is not absolutely studied therefore their application is still limited except for oxide of the zinc (ZnO) used as the converter and in production of the gluing tapes and plasters.
In addition oxide of zinc is applied in varistors, gas sensors, blue light-emitting diodes, biological sensors. The semiconductor and for a covering of windowpanes for the purpose of reflection of infrared light is used, he can be met in LCD displays and solar batteries.
Layered crystals represent the double connections similar to a lead diiodid, a disulfide of molybdenum and selenide of gallium. They differ in the layered structure of a crystal where covalent communications of significant force work. Semiconductors of this kind are interesting that electrons behave in layers quasi-dvumerno. Interaction of layers changes introduction to composition of third-party atoms. The disulfide of molybdenum (MoS2) is applied in high-frequency rectifiers, detectors, transistors, memristors.
Organic semiconductors are a wide class of substances: naphthalene, anthracene, polydiacetylene, ftalotsianida, polyvinylcarbazole. They have an advantage before inorganic: it is easy for them to give the necessary qualities. They have considerable optical nonlinearity and therefore are widely used to optoelectronics.
Crystal allotropa of carbon belong to semiconductors too:
- Fullerene with structure in the form of the convex closed polyhedron.
- Graphene with a one-atomic layer of carbon has the record heat conductivity and mobility of electrons increased by rigidity.
- Nanotubes – the graphite plates curtailed into a tube in nanometers in the diameter. Depending on coupling can show metal or semiconductor qualities.
Examples of magnetic semiconductors: europium sulfide, selenide of europium and solid solutions. The maintenance of magnetic ions affects magnetic properties, antiferromagnetism and ferromagnetics. Strong magnetooptical effects of magnetic semiconductors allow to use them for optical modulation. They are applied in radio engineering, optical devices, in wave guides of microwave devices.
Semiconductor ferroelectric material differs in existence in them of the electric moments and emergence of spontaneous polarization. Example of semiconductors: titanate of lead (PbTiO3), Germany telluride (GeTe), BaTiO3 barium titanate, SnTe tin telluride. At low temperatures have properties of a ferroelectric material. These materials are applied in the memorable, nonlinear and optical devices and piezoelectric sensors.