Dependence of electron mobility on spatial separation of electrons and donors in Al<i>x</i>Ga1−<i>x</i>As/GaAs heterostructures

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.