Modulation doping is a technique for fabricating semiconductors such that the free charge carriers are spatially separated from the donors. Because this eliminates scattering from the donors, modulation-doped semiconductors have very high carrier

mobilities Mobilities is a contemporary paradigm in the social sciences that explores the movement of people (human migration, individual mobility, travel, transport), ideas (see e.g. meme) and things (transport), as well as the broader social implications of ...

History

Modulation doping was conceived in

Bell Labs Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...

in 1977 following a conversation between Horst Störmer and Ray Dingle, and implemented shortly afterwards by

Arthur Gossard Arthur C. Gossard (June 18, 1935 – June 26, 2022) was a professor of materials and electrical engineering at the University of California, Santa Barbara. In 1982, he co-discovered the fractional quantum Hall effect. His research is related to mol ...

. Störmer and Dan Tsui used a modulation-doped wafer to discover the

fractional quantum Hall effect The fractional quantum Hall effect (fractional QHE or FQHE) is the observation of precisely quantized plateaus in the Hall conductance of 2-dimensional (2D) electrons at fractional values of e^2/h, where ''e'' is the electron charge and ''h'' i ...

Implementation

Modulation-doped semiconductor crystals are commonly grown by

epitaxy Epitaxy (prefix ''epi-'' means "on top of”) is a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited cry ...

to allow successive layers of different semiconductor species to be deposited. One common structure uses a layer of AlGaAs deposited over GaAs, with Si n-type donors in the AlGaAs.

Applications

Field effect transistors

Modulation-doped

transistors A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

can reach high electrical mobilities and therefore fast operation. A modulation-doped field-effect transistor is known as a MODFET.

Low-temperature electronics

One advantage of modulation doping is that the charge carriers cannot become trapped on the donors even at the lowest temperatures. For this reason, modulation-doped heterostructures allow electronics to be operated at

cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...

temperatures.

Quantum computing

Modulation-doped

two-dimensional electron gas A two-dimensional electron gas (2DEG) is a scientific model in solid-state physics. It is an Fermi gas, electron gas that is free to move in two dimensions, but tightly confined in the third. This tight confinement leads to quantized energy levels ...

es can be gated to create

quantum dots Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic i ...

Electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

trapped in these dots can then be operated as quantum bits.

References

{{Reflist Semiconductor device fabrication