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.