Anomalous Hall-effect results in low-temperature molecular-beam-epitaxial GaAs: Hopping in a dense<i>EL</i>2-like band

Abstract

Molecular-beam-epitaxial GaAs grown at very low temperatures (\ensuremath{\sim}200 \ifmmode^\circ\else\textdegree\fi{}C) exhibits anomalous Hall-effect properties. Here we show conclusively that the room-temperature conduction is due to activated (nearest-neighbor) hopping in a deep defect band of concentration 3\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, and energy ${\mathit{E}}_{\mathit{c}}$-0.75 eV, along with conduction due to free carriers thermally excited from this band. At low measurement temperatures, variable-range hopping [\ensuremath{\sigma}\ensuremath{\propto}exp(-${\mathit{T}}_{0}$/T${)}^{1/4}$] prevails. The conduction-band mobility can be well explained by neutral-deep-donor scattering in parallel with lattice scattering.