Metamorphic In x Ga 1− x As/InAlAs ( x ⩾ 0.8) modulation doped heterostructures have been grown on GaAs using a linearly graded In(AlGa)As buffer layer, and their structural and electric properties have been investigated. Surface morphology was found to depend on growth temperature and graded buffer thickness. Low growth temperature resulted in a relatively smooth surface with a minimum root-mean-square roughness value of 4–7 nm. The In(AlGa)As graded buffer effectively prevented dislocations from threading into the top layers. The epilayer grown on the graded buffer was tilted and not fully relaxed. High electron mobility and sheet density were achieved. The highest mobility value was 13740 cm 2 /Vs with a carrier density of 1.9 · 10 12 cm −2 at 300 K. These values are comparable with InP-based InGaAs/InAlAs modulation doped heterostructures.
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Wang et al. (1997) studied this question.