EXTREMELY HIGH-MOBILITY 2-DIMENSIONAL ELECTRON-GAS - EVALUATION OF SCATTERING MECHANISMS

We report on the characterization of selectively doped GaAs/AlGaAs het erostructures, grown by an extremely clean molecular beam epitaxy syst em, which exhibit a Hall mobility of a two dimensional electron gas ex ceeding 10X10(6) cm(2)/Vs for a wide range of undoped spacer layer thi ckness (50-100 nm). A maximum electron mobility of 14.4X10(6) cm(2)/Vs was measured at 0.1 K in a structure with a 68 nm spacer thickness an d an areal carrier density of 2.4X10(11) cm(-2). This is the highest e lectron mobility ever reported, leading to a momentum relaxation mean- free path of similar to 120 mu m. We present experiments that enable u s to distinguish between the main scattering mechanisms. We find that scattering due to background impurities limits electron mobility in ou r best samples, suggesting that further improvement in structure quali ty is possible. (C) 1997 American Institute of Physics.