Ballistic transport in semiconductor alloys

Abstract

The electronic structure of semiconductor compounds GaAs, InAs, and InP and alloys Ga0.5In0.5As, Ga0.7Al0.3As, and InP0.5As0.5, obtained in the coherent potential approximation, is used to calculate the group velocity and velocity relaxation time limited by longitudinal optical phonons, alloy disorder, and ionized impurities as a function of electron energy at 300 K. The nonparabolic nature of the band structure is found to severely limit the electron mean free path. With the types of interactions considered to date, the presence of L valleys does not limit the mean free path of electrons moving in the 〈100〉 direction. At 1018-cm−3 doping, electron-electron interactions reduce the mean free path by only 15% to 20%. InAs and GaInAs alloys offer advantages over all the other materials for devices with base widths greater than 500 Å; however, for thinner devices, ∼100 Å, no material is appreciably better than GaAs, the III-V compound currently under best control. The ballistic device-related properties of several II-VI systems compare favorably with the III-V alloys studied here. However, the II-VI compounds are less robust structural materials leading us to recommend the III-V compounds.