High-electron mobility transistor

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Cross-section of an InGaAs pseudomorphic HEMT

The high-electron-mobility transistor ( HEMT , dt. "Transistor with high electron mobility") is a special design of the field effect transistor for very high frequencies and is a special design of a MESFET .

Other names for this type of transistor are modulation-doped field-effect transistor (MODFET), two-dimensional electron-gas field-effect transistor (TEGFET), selectively-doped heterojunction transistor (SDHT) and heterojunction field-effect transistor (HFET).

It was developed by Takashi Mimura and colleagues at Fujitsu in 1979 .

Structure and functionality

Energy band diagram of a HEMT with 2D electron gas

It consists of layers of different semiconductor materials with band gaps of different sizes (see heterostructure ). The material system aluminum gallium arsenide / gallium arsenide (AlGaAs / GaAs) is often used, with the AlGaAs being highly n-doped and the GaAs not being doped. Since the band gap of AlGaAs is larger than that of GaAs, a two-dimensional electron gas (2DEG) forms at the interface of these two materials on the GaAs side , which can serve as a conductive channel. The electron mobility is very high in it.

It can be further improved by modulation doping of the AlGaAs, as suggested for the first time by Horst Störmer and others . This reduces the electron scattering of the 2DEG at charged impurities and thus leads to a further increase in charge carrier mobility, which was a prerequisite for the discovery of the fractional quantum Hall effect ( 1998 Nobel Prize in Physics ).

The HEMT principle can also be applied to other material systems such as InGaAs / InP / AlInAs, AlGaN / GaN , AlInN / GaN and Si / SiGe .

Current research focuses on material combinations of gallium nitride (GaN) and aluminum gallium nitride ( AlGaN) or aluminum indium nitride (AlInN), which, due to its comparatively high band gap, enables a higher operating voltage before a field breakdown occurs. This material combination proves to be particularly advantageous for the production of power transistors, since the output impedance increases with the same power and thus the decoupling of the power is simplified (adaptation). Deposited on silicon carbide (SiC), it also has a lower thermal resistance than GaAs material combinations, which has a positive effect on the maximum power loss or service life and reliability.

scope of application

The HEMT is well suited for high-frequency applications due to its high charge carrier mobility . The component is controlled, similar to the metal-semiconductor field-effect transistor , via a metal gate which is connected to the n-AlGaAs layer.

literature

  • Werner Bächtold, Otto Mildenberger: microwave electronics . Vieweg + Teubner Verlag, 2002, ISBN 3-528-03937-X , p. 49 ff .

Individual evidence

  1. ^ KK Ng: A survey of semiconductor devices . In: IEEE Transactions on Electron Devices . tape 43 , no. 10 , 1996, pp. 1760-1766 , doi : 10.1109 / 16.536822 .
  2. ↑ T. Mimura, S. Hiyamizu, T. Fujii, K. Nanbu: A New Field-Effect Transistor with Selectively Doped GaAs / n-AlxGa1-xAs Heterojunctions , Japanese Journal of Applied Physics, Volume 19, 1980, L 225-L227
  3. ↑ T. Mimura, Kazukiyo Joshin, Satoshi Hiyamizu, Kohki Hikosaka, Masayuki Abe: High Electron Mobility Transistor Logic , Japanese Journal of Applied Physics, Volume 20, 1981, L 598
  4. ↑ T. Mimura: Development of High Electron Mobility Transistor , Japanese Journal of Applied Physics, Volume 44, 2005, p. 8263