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

Abstract

Single‐period modulation doped A1_xGa_1−x As/GaAs heterojunctions have been prepared by molecular beam epitaxy (MBE). Heterojunctions with a Si‐doped A1_xGa_1−x As layer grown on an unintentionally doped GaAs layer have exhibited enhanced mobility at 78 ° and 300 °K. The A1_xGa_1−x As, grown with x = 0.25 or x = 0.33, was doped to a level N_D?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.