Heterojunctions and Interfaces
The presence of an inversion or accumulation layer of charge, either electrons or holes, at the surface of certain heterojunctions was predicted many decades ago. This is true whether the heterojunction is between two semiconductors, such as in the high-electron-mobility transistor, or between a semiconductor and an oxide (or free space), such as in an MOS device. Of course, this latter method of controlling surface (or interface) charge is the preferred approach to current very large scale integration (VLSI) in silicon, where the control over the charge is exercised by the gate MOS structure in the MOSFET. In contrast to this, early transistors in GaAs were prepared using the metal-gate technology for MESFETs, primarily because of the lack of a good oxide technology in GaAs. The approach to GaAs changed in 1978, when Dingle et al. (1) demonstrated that very high mobilities could be achieved in modulation-doped structures through growth by molecular-beam epitaxy (MBE).
KeywordsGate Voltage Depletion Region Inversion Layer Coulomb Scattering Inversion Density
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