HighElectronMobility

High electron mobility describes the property of a material or device in which electrons can move through the lattice with relatively little scattering, resulting in large drift velocities under an applied electric field. Electron mobility μ is defined as the drift velocity per unit electric field and is commonly measured in cm^2 per volt-second. In practice, mobility, together with carrier concentration, determines a material’s conductivity and strongly influences transistor speed and drive current. Mobility can be probed by Hall effect measurements, which yield the Hall mobility and related parameters.

Materials with high electron mobility include many III–V semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP), and their alloys. These materials routinely exhibit electron mobilities well above silicon and, in structured devices such as modulation-doped heterojunctions, can form high-quality two-dimensional electron gases (2DEGs) with mobilities surpassing 10^5 cm^2/(V·s) at low temperatures, enabling very fast transistors. Graphene and other two-dimensional materials offer very high intrinsic mobilities, though practical devices must contend with substrate and impurity scattering. Strained silicon and silicon–germanium alloys can also increase electron mobility in mainstream CMOS technology.

Applications of high-mobility materials include high-speed and high-frequency electronics, such as high-electron-mobility transistors (HEMTs) for RF amplifiers, and fast switching in microprocessors and optical communication components. Material design strategies to raise mobility focus on reducing impurity and phonon scattering, achieving high-quality interfaces in heterostructures, and employing carrier confinement in quantum wells or 2D materials.