High-Field Electron-Drift Velocity in n-Type Modulation-Doped GaAs_0.96Bi_0.04 Quantum Well Structure

The drift velocity (v_drift) of electrons in an n-type modulation-doped GaAs_0.96Bi_0.04/Al_0.15Ga_0.85As quantum well (QW) structure is determined for electric fields (F) ranging from ≈0.4 to 3.58 kV cm⁻¹. The resulting v_drift characteristic exhibited a linear increase and reached ≈6 × 10⁶ cm s⁻¹ at low electric fields then almost saturated with increasing electric field. The electron drift mobility is determined as 2265 cm² Vs⁻¹ in the regime where the drift velocity is linear with respect to the electric field. The drift velocity saturates at ≈6.1 × 10⁶ cm s⁻¹ at the electric fields between ≈2.7 and 3.4 kV cm⁻¹. Saturation of the drift velocity is attributed to the transfer of the electrons from the QW layer (GaAs_0.96Bi_0.04) with higher electron mobility to the barrier layer (Al_0.15Ga_0.85As) and satellite valley L-valley with lower electron mobility, which initiates cooling of electrons via phonon scattering in the sample.