Abstract
Morphological and physical properties of Al0.48In0.52As/Ga 0.47In0.53As heterostructures grown by molecular beam epitaxy, lattice relaxed on GaAs substrates and lattice matched on InP substrates, are presented. Both a quaternary linear and step graded lattice relaxed buffer concept is implemented to accomodate the lattice mismatch between the GaAs substrate and the Al0.48In0.52As/Ga 0.47In0.53As layer sequence. The surface morphology and the transport properties of Al0.48In0.52As/Ga0.47In0.53As high electron mobility transistor structures were studied by atomic force microscopy and Hall effect measurements, respectively. Optical properties were investigated by low temperature photoluminescence experiments on quantum well structures. The linear graded buffer approach was found to result in superior heterostructure properties due to the two dimensional growth mode during the whole growth process resulting in the typical cross hatched surface morphology. In contrast, the use of step graded buffer layers resulted in three dimensional layer growth and inferior layer quality. However, by increasing the number of steps, i.e., reducing the change in the lattice constant for each step and thus approaching a linear grading, two dimensional growth is recovered.
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