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, and implemented shortly afterwards by Arthur Gossard. In 1977, 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.
Applications
Field effect transistors
Modulation-doped transistors 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 operating 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.
References
- Horst L. Störmer, Nobel Biography
- Gossard, A. C. (1985). "Modulation Doping of Semiconductor Heterostructures". Molecular Beam Epitaxy and Heterostructures. pp. 499–531. doi:10.1007/978-94-009-5073-3_14. ISBN 978-94-010-8744-5.
- L.D. Nguyen; L.E. Larson; U.K. Mishra (2009). "Ultra-high speed modulation-doped field-effect transistors: a tutorial review". Proc. IEEE. 80 (4): 494. doi:10.1109/5.135374.
- Global Standards for the Microelectronics Industry - modulation-doped field-effect transistor (MODFET)
- Hanson, R.; Kouwenhoven, L. P.; Petta, J. R.; Tarucha, S.; Vandersypen, L. M. K. (2009). "Spins in few-electron quantum dots". Rev. Mod. Phys. 79 (2): 1217. arXiv:cond-mat/0610433. Bibcode:2007RvMP...79.1217H. doi:10.1103/RevModPhys.79.1217. S2CID 9107975.