modulation doping
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.
History
Modulation doping was conceived in Bell Labs in 1977 following a conversation between Horst Störmer and Ray Dingle,[https://www.nobelprize.org/nobel_prizes/physics/laureates/1998/stormer-bio.html Horst L. Störmer, Nobel Biography] and implemented shortly afterwards by Arthur Gossard. Störmer and Dan Tsui used a modulation-doped wafer to discover the fractional quantum Hall effect.
Implementation
Modulation-doped semiconductor crystals are commonly grown by epitaxy 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.{{Cite book | doi=10.1007/978-94-009-5073-3_14|chapter = Modulation Doping of Semiconductor Heterostructures|title = Molecular Beam Epitaxy and Heterostructures| pages=499–531|year = 1985|last1 = Gossard|first1 = A. C.| isbn=978-94-010-8744-5}}
Applications
=Field effect transistors=
Modulation-doped transistors can reach high electrical mobilities and therefore fast operation.{{cite journal|author1=L.D. Nguyen |author2=L.E. Larson |author3=U.K. Mishra |title= Ultra-high speed modulation-doped field-effect transistors: a tutorial review| journal= Proc. IEEE|volume= 80|issue= 4|page= 494|year=2009|doi=10.1109/5.135374}} A modulation-doped field-effect transistor is known as a MODFET.[https://www.jedec.org/standards-documents/dictionary/terms/modulation-doped-field-effect-transistor-modfet Global Standards for the Microelectronics Industry - modulation-doped field-effect transistor (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 temperatures.
=Quantum computing=
Modulation-doped two-dimensional electron gases can be gated to create quantum dots. Electrons trapped in these dots can then be operated as quantum bits.{{cite journal|first1=R. |last1=Hanson|first2=L. P. |last2=Kouwenhoven|first3=J. R. |last3=Petta|first4=S. |last4=Tarucha|first5=L. M. K. |last5=Vandersypen|title= Spins in few-electron quantum dots| journal= Rev. Mod. Phys.|volume= 79|issue= 2|page= 1217 |year=2009|doi = 10.1103/RevModPhys.79.1217|arxiv= cond-mat/0610433|bibcode= 2007RvMP...79.1217H|s2cid= 9107975}}
References
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