Saturated Low-Temperature Conductivity in Ultrafast Semiconductor Nanocomposites

This Letter presents studies on low-field electrical conduction in the range of 4-300 K for an ultrafast material, i.e., InGaAs:ErAs grown by molecular beam epitaxy. The unique properties include nano-scale ErAs crystallites in the host semiconductor InGaAs, a deep Fermi level and picosecond ultrafast photocarrier recombination. As the temperature drops, the conduction mechanisms are in the sequence of: thermal activation, nearest-neighbor hopping, and variable-range hopping. In the low-temperature limit, finite-con-ductivity metallic behavior, not insulating, was observed. This unusual conduction behavior, related to the nanometer-scale ErAs crystallite islands, is explained with the Abrahams scaling theory. Current vs. temperature for (A) InGaAs:ErAs - the ultrafast nanocomposite; and (C) an undoped InGaAs.