Physical limits of heterostructure field-effect transitors and possibilities of novel quantum field-effect devices

Physical processes which govern the switching speed of heterostructure field-effect transistors, including high-electron mobility transistors, are discussed to show that the ultimate switching speed is of the order of one ps. The importance of adopting new FET structures with higher current-drive capability is pointed out, including selectively-doped double-hetero structures and material systems other than GaAs-AlGaAs. Possibilities of novel field-effect devices, such as velocity modulation transistors, quantum-well-wire FET´s with extremely high electron mobilities, and field-effect 2-dimensional-electron-gas superlattices are also discussed. The concept of wavefunction engineering in these devices is described.