Mobility Enhancement in Inverted AlxGa1-xAs/GaAs Modulation Doped Structures and Its Dependence on Donor-Electron Separation

Abstract
Inverted single period modulation doped Al x Ga1-x As/GaAs heterostructures with the binary compound on top of the ternary, exhibiting enhanced electron mobilities, were grown by molecular beam epitaxy. Despite the early reports of no mobility enhancement, considerable mobility enhancement was obtained simply by growing the structures at extremely high substrate temperatures. Similar to the case where the ternary is on top of the binary, the electron mobility was observed to be strongly dependent on the spacing between the ionized donors and the electron gas. Electron mobilities as high as 30,400 cm2/Vs at 78 K and 37,900 cm/Vs at 10 K were observed in structures having a net electron concentration of about 5×1011 cm-2.