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Extremely high-mobility two dimensional electron gas



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Extremely high mobility two dimensional electron gas Evaluation of scattering mechanisms V Umansky a R de Picciotto and M Heiblum Department of Condensed Matter Physics Braun Center for Submicron Research Weizmann Institute of Science Rehovot 76100 Israel Received 16 April 1997 accepted for publication 31 May 1997 We report on the characterization of selectively doped GaAs AlGaAs heterostructures grown by an extremely clean molecular beam epitaxy system which exhibit a Hall mobility of a two dimensional electron gas exceeding 103106 cm2 Vs for a wide range of undoped spacer layer thickness 50 100 nm A maximum electron mobility of 14 43106 cm2 Vs was measured at 0 1 K in a structure with a 68 nm spacer thickness and an areal carrier density of 2 431011 cm22 This is the highest electron mobility ever reported leading to a momentum relaxation mean free path of 120 mm We present experiments that enable us to distinguish between the main scattering mechanisms We find that scattering due to background impurities limits electron mobility in our best samples suggesting that further improvement in structure quality is possible 1997 American Institute of Physics S0003 6951 97 01231 X Since the first fabrication of a high mobility two dimensional electron gas 2DEG 1 embedded in a GaAs AlGaAs heterostructure employing the concept of spatial separation between ionized parent donor impurities and the resultant 2DEG has led to a wide range of structures with electron mobility exceeding 13106 cm2 Vs 2 Utilizing extremely clean molecular beam epitaxy MBE systems led to successive improvements with recent low temperature mobility values exceeding 13107 cm2 Vs Refs 3 5 with a record mobility of 11 73106 cm2 Vs Ref 3 A number of theoretical works calculated the mobility in such structures from the first principles accounting for a variety of scattering mechanisms 2 6 11 Most models qualitatively describe the experimental results well however they usually fail quantitatively Moreover



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