Transport in strain relaxed In0.15Al0.85As/In0.17Ga0.83As heterojunctions

Abstract

The electrical and galvanomagnetic properties of the two-dimensional electron gas (2DEG) in δ-doped and modulation doped strain–relaxed In0.15Al0.85As/In0.17Ga0.83As heterojunctions have been determined, as a function of sheet carrier density, by temperature dependent resistivity Hall and 1.6 K Shubnikov de Haas (SdH) oscillatory magnetoresistance measurements. The structures were grown by molecular-beam epitaxy on misoriented (001) GaAs substrates; strain relaxation, confirmed by double crystal x-ray diffraction, was obtained by means of step graded InxGa1−xAs buffer layers with x=0.10, and x=0.15 steps of 0.3 μm in thickness. Low temperature (1.6 K) SdH measurements confirm the presence of well behaved 2DEG layers with negligible parallel conduction, and single band occupancy for sheet carrier densities ranging from 7.4×1011 cm−2 to 1.0×1012 cm−2, and respective mobilities of 7.5×104 cm2/V s and 6.1×104 cm2/V s. Low field resistivity and Hall measurements suggest a transition, at a sheet carrier density of approximately 1012 cm−2, from an alloy scattering dominated mobility, to a mobility limited by ionized impurity scattering. The excellent transport properties of the 2DEG channels suggests the use of strain relaxation by means of appropriate buffer layers for heterostructure devices grown on gallium arsenide substrates.