The two-dimensional electron gas and its technical applications

Two-dimensional systems constituted by III–V compound semiconductor heterojunctions are first recalled. Optical properties of double heterojunction quantum wells (QW) and transport properties in selectively-doped heterojunction two-dimensional electron gas (2DEG) are described. In particular quantum effects associated with the two-dimensional character of these systems (intersubband transitions, step-like density of states, Shubnikov-de Haas oscillations, quantized Hall effects …) are pointed out. The reduced electron-impurity scattering and the enhanced screening effect in the 2DEG is also studied. Electronic devices using two-dimensional systems have been found to exhibit higher performances than conventional devices: ultra low threshold current and low temperature-sensitivity for QW lasers and super-low noise amplification and high speed-low power circuit integration for two-dimensional electron gas FETs (TEGFETs). Interpretations of these high performances are given. These devices which are the basic foundation of modern electronics (optical fiber communication, satellite communication, super-computer …) illustrate the tremendous interest of two-dimensional systems.