Chapter 5 Heterostructure and Compound Semiconductor Devices

Many types of microwave low-noise amplifiers, mixers, and up-converters are cryogenically cooled to achieve the lowest noise possible. The chapter describes the room-temperature devices that present considerable reduced noise at cryogenic temperatures: the GaAs field-effect transistors (GaAs FETs), metal semiconductor field-effect transistor (MESFET), and junction FET (JFET). GaAs FETs should be a better choice for low-power, low-noise applications under deep cryogenic conditions because it is possible to degenerate the GaAs material at practical doping concentrations. The advantage of Si devices in terms of operation at reduced noise is overcome with the cooling of the GaAs devices. The chapter describes the fabrication, physics, device, characterization and modeling, high-frequency performance, and circuit applications of high electron mobility transistors (HEMTs). The chapter briefly reviews the possible operation of III—V compound semiconductor heterojunction bipolar transistors (HBTs) at low-temperature. A simple but important example of a “quantum-scale” device exhibiting quantum confinement and coupling is the resonant tunneling diodes (RTDs). The chapter discusses the important physical, material, and electronic properties of RTDs.