Semiconductor device
A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material for its function. Its conductivity lies between conductors and insulators. Semiconductor devices have replaced vacuum tubes in most applications. They conduct electric current in the solid state, rather than as free electrons across a vacuum or as free electrons and ions through an ionized gas.
Semiconductor devices are manufactured both as single discrete devices and as integrated circuits, which consist of two or more devices—which can number from the hundreds to the billions—manufactured and interconnected on a single semiconductor wafer.
Semiconductor materials are useful because their behavior can be easily manipulated by the deliberate addition of impurities, known as doping. Semiconductor conductivity can be controlled by the introduction of an electric or magnetic field, by exposure to light or heat, or by the mechanical deformation of a doped monocrystalline silicon grid; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs due to mobile or "free" electrons and electron holes, collectively known as charge carriers. Doping a semiconductor with a small proportion of an atomic impurity, such as phosphorus or boron, greatly increases the number of free electrons or holes within the semiconductor. When a doped semiconductor contains excess holes, it is called a p-type semiconductor ; when it contains excess free electrons, it is called an n-type semiconductor. A majority of mobile charge carriers have negative charges. The manufacture of semiconductors controls precisely the location and concentration of p- and n-type dopants. The connection of n-type and p-type semiconductors form p–n junctions.
The most common semiconductor device in the world is the MOSFET, also called the MOS transistor. As of 2013, billions of MOS transistors are manufactured every day. Semiconductor devices made per year have been growing by 9.1% on average since 1978, and shipments in 2018 are predicted for the first time to exceed 1 trillion, meaning that well over 7 trillion have been made to date.
Main types
Diode
A semiconductor diode is a device typically made from a single p–n junction. At the junction of a p-type and an n-type semiconductor, there forms a depletion region where current conduction is inhibited by the lack of mobile charge carriers. When the device is forward biased, this depletion region is diminished, allowing for significant conduction. Contrariwise, only a very small current can be achieved when the diode is reverse biased.Exposing a semiconductor to light can generate electron–hole pairs, which increases the number of free carriers and thereby the conductivity. Diodes optimized to take advantage of this phenomenon are known as photodiodes.
Compound semiconductor diodes can also produce light, as in light-emitting diodes and laser diode
Transistor
Bipolar junction transistor
are formed from two p–n junctions, in either n–p–n or p–n–p configuration. The middle, or base, the region between the junctions is typically very narrow. The other regions, and their associated terminals, are known as the emitter and the collector. A small current injected through the junction between the base and the emitter changes the properties of the base-collector junction so that it can conduct current even though it is reverse biased. This creates a much larger current between the collector and emitter, controlled by the base-emitter current.Field-effect transistor
Another type of transistor, the field-effect transistor, operates on the principle that semiconductor conductivity can be increased or decreased by the presence of an electric field. An electric field can increase the number of free electrons and holes in a semiconductor, thereby changing its conductivity. The field may be applied by a reverse-biased p–n junction, forming a junction field-effect transistor or by an electrode insulated from the bulk material by an oxide layer, forming a metal–oxide–semiconductor field-effect transistor.Metal-oxide-semiconductor
The metal-oxide-semiconductor FET, a solid-state device, is by far the most used widely semiconductor device today. It accounts for at least 99.9% of all transistors, and there have been an estimated 13sextillion MOSFETs manufactured between 1960 and 2018.The gate electrode is charged to produce an electric field that controls the conductivity of a "channel" between two terminals, called the source and drain. Depending on the type of carrier in the channel, the device may be an n-channel or a p-channel MOSFET. Although the MOSFET is named in part for its "metal" gate, in modern devices polysilicon is typically used instead.
Other types
Two-terminal devices:- DIAC
- Diode
- Gunn diode
- IMPATT diode
- Laser diode
- Light-emitting diode
- Photocell
- Phototransistor
- PIN diode
- Schottky diode
- Solar cell
- Transient-voltage-suppression diode
- Tunnel diode
- VCSEL
- Zener diode
- Zen diode
- Bipolar transistor
- Darlington transistor
- Field-effect transistor
- Insulated-gate bipolar transistor
- Silicon-controlled rectifier
- Thyristor
- TRIAC
- Unijunction transistor
- Hall effect sensor
- Photocoupler
Materials
Germanium was a widely used early semiconductor material but its thermal sensitivity makes it less useful than silicon. Today, germanium is often alloyed with silicon for use in very-high-speed SiGe devices; IBM is a major producer of such devices.
Gallium arsenide is also widely used in high-speed devices but so far, it has been difficult to form large-diameter boules of this material, limiting the wafer diameter to sizes significantly smaller than silicon wafers thus making mass production of GaAs devices significantly more expensive than silicon.
Gallium Nitride is gaining popularity in high-power applications including power ICs, light-emitting diodes, and RF components due to its high strength and thermal conductivity. Compared to silicon, GaN's band gap is more than 3 times wider at 3.4 eV and it conducts electrons 1,000 times more efficiently.
Other less common materials are also in use or under investigation.
Silicon carbide is also gaining popularity in power ICs and has found some application as the raw material for blue LEDs and is being investigated for use in semiconductor devices that could withstand very high operating temperatures and environments with the presence of significant levels of ionizing radiation. IMPATT diodes have also been fabricated from SiC.
Various indium compounds are also being used in LEDs and solid-state laser diodes. Selenium sulfide is being studied in the manufacture of photovoltaic solar cells.
The most common use for organic semiconductors is organic light-emitting diodes.
Applications
All transistor types can be used as the building blocks of logic gates, which are fundamental in the design of digital circuits. In digital circuits like microprocessors, transistors act as on-off switches; in the MOSFET, for instance, the voltage applied to the gate determines whether the switch is on or off.Transistors used for analog circuits do not act as on-off switches; rather, they respond to a continuous range of inputs with a continuous range of outputs. Common analog circuits include amplifiers and oscillators.
Circuits that interface or translate between digital circuits and analog circuits are known as mixed-signal circuits.
Power semiconductor devices are discrete devices or integrated circuits intended for high current or high voltage applications. Power integrated circuits combine IC technology with power semiconductor technology, these are sometimes referred to as "smart" power devices. Several companies specialize in manufacturing power semiconductors.