Quantum and classical mobility determination of the dominant scattering mechanism in the two-dimensional electron gas of an AlGaAs/GaAs heterojunction

Abstract

Recent theoretical and experimental interest has focused on the issue of the dominant scattering mechanism which limits the mobility of the two-dimensional electron gas formed at the molecular-beam-epitaxy (MBE) interface of an AlGaAs/GaAs heterojunction. Measurements have been made at 1.3 K with MBE-grown AlGaAs/GaAs heterojunctions, indicating a difference of nearly an order of magnitude between transport scattering times, expressed as a mobility, measured via either the Hall mobility (classical scattering time) or from the de Haas–Shubnikov oscillation envelope (quantum scattering time). This result is contrasted with measurements from the qualitatively different Si metal-oxide-semiconductor field-effect transistor (MOSFET) interface where, over the same charge-density region, the two mobilities are nearly equal and limited by interface roughness scattering. The ratio of the quantum-to-classical scattering time from competing scattering mechanisms is calculated. The observed low ratio in the heterostructures is in excellent agreement with the calculated screened-Coulomb scattering from residual charge centers in the AlGaAs, while the lack of this effect in the MOSFET’s is in excellent agreement with the surface roughness calculation. The measured scattering-time ratio is thus a new method of directly selecting the dominant scattering mechanism among competing effects. Stray effects which could interfere with the quantum measurements are discussed.