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.

## Contents

* 1 History
* 2 Implementation
* 3 Applications
* 3.1 Field effect transistors
* 3.2 Low-temperature electronics
* 3.3 Quantum computing
* 4 References

## History

Modulation doping was conceived in Bell Labs in 1977 following a conversation between Horst Störmer and Ray Dingle,[1] 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.[2]

## Applications

### Field effect transistors

Modulation-doped transistors can reach high electrical mobilities and therefore fast operation.[3] A modulation-doped field-effect transistor is known as a MODFET.[4]

### 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.[5]

## References

1. ↑ Horst L. Störmer, Nobel Biography
2. ↑ 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.
3. ↑ 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.
4. ↑ Global Standards for the Microelectronics Industry - modulation-doped field-effect transistor (MODFET)
5. ↑ R. Hanson, L. P. Kouwenhoven, J. R. Petta, S. Tarucha, and L. M. K. Vandersypen (2009). "Spins in few-electron quantum dots". Rev. Mod. Phys. 79 (2): 1217. doi:10.1103/RevModPhys.79.1217. Bibcode: 2007RvMP...79.1217H.

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