Two-Dimensional Electron Gas Mobility Enhancement in Inverted GaAs/n-AlGaAs Heterostructures Grown by Molecular Beam Epitaxy

Electrical properties of an inverted heterojunction interface in GaAs/n-AlGaAs heterostructures selectively doped with Si were investigated. It was found that the effect of mobility reduction normally observed in such structures can be overcome by suppressing Si doping in the AlGaAs layer and increasing the spacer layer thickness. The results indicate a strong contribution, based on a diffused profile of doped Si impurities in the GaAs channel and AlGaAs spacer, resulting from surface segregation. Large enhancement of two-dimensional electron gas (2DEG) mobility at low temperature was achieved in an inverted heterostructure at a low Si doping concentration (Nd=3×1017 cm-3) and spacer thickness exceeding 100 A. The highest mobility value obtained was 5×104 cm2/V·s at 77 K, with an interface carrier density Ns of around 1.7×1011 cm-2.