Scanning Microscopy


We investigate compositionally graded Inxo≤x≤0.5Ga1-xAs and InP buffer layers which are prepared by molecular beam epitaxy on (001) GaAs substrate. The initial In content xo is equal to 0, 0.12, 0.18, 0.24, and 0.5 for the different samples. The In composition of the graded buffer increases linearly between xo and 0.5 with a fixed slope of 50% In-content per μm. The idea was to combine the advantage of surface flatness in homogeneous buffer layers and the reduced density of threading dislocations on the surface for graded buffer layers. The best compromise in terms of photoluminescence intensity and linewidth, electron mobility and crystal quality is achieved for xo = 0.18. For comparison to the InGaAs layers, we investigated also homogenous InP buffer layers on GaAs substrate. A strong photoluminescence peak with a linewidth of 5 meV is observed for 1 μm InP grown at 450°C applying a GaP decomposition source. The density of threading dislocations in the surface region is lower than in relaxed In0.5Ga0.5As layers but still by far not as low as for the graded buffer layers.

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