Dependence of electron mobility on spatial separation of electrons and donors in AlxGa1−xAs/GaAs heterostructures

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Abstract
Single‐period modulation doped A1xGa1−x As/GaAs heterojunctions have been prepared by molecular beam epitaxy (MBE). Heterojunctions with a Si‐doped A1xGa1−x As layer grown on an unintentionally doped GaAs layer have exhibited enhanced mobility at 78 ° and 300 °K. The A1xGa1−x As, grown with x = 0.25 or x = 0.33, was doped to a level ND?3×1017 cm−3 resulting in a sheet‐charge density of about 8×1011 cm−2. Maximum mobilities of 74 200 cm2/V s at 78 °K and 6930 cm2/V s at 300 °K were observed in different structures. This represents an improvement of more than a factor of 2 over the best previously reported results at 78 °K. These structures, if used for normally off and/or psuedonormally off FET channel layers in high‐speed integrated circuits, can provide improved performance. These extremely high mobilities can lead to a power delay product improvement of about a factor of 2 at room temperature and a factor of more than 12 at liquid‐nitrogen temperature as compared to conventional structures. This increase in mobility is the result of the virtual elimination of electron scattering by spacially separating the donors from the heterojunction interface.