Two-Dimensional Electron Optics in GaAs

Electron mobilities in modulation-doped GaAs-AlGaAs heterostructures [1] presently exceed values of 10 sup 7 cm sup 2 /Vsec at low temperatures, equivalent to elastic mean free paths of ~100 micrometers. These are macroscopic distances on the length scale of today's semiconductor fabrication techniques. Electronic transport in such materials can no longer be regarded as diffusive. Instead, low-energy electron propagation is ballistic and a large fraction of the carriers traverse typical device distances without a serious scattering event.