Molecular beam epitaxy of Al(0.48)In(0.52)As/Ga(0.47)In(0.53)As heterostructures on metamorphic Al(x)Ga(y)In(1-x-y)As buffer layers

Ternary Al(x)In(1-x)As/Ga(y)In(1-y)As heterostructures with a lattice mismatch up to 4 per cent are grown on GaAs by molecular beam epitaxy. Two buffer layer concepts to compensate the lattice misfit between the Al(x)In(1-x)As/Ga(y)In(1-y)As layers and the GaAs substrate using the quaternary Al(x)Ga(y)In(1-y)As in a linear graded and two-step graded fashion, respectively, are presented. The Al and Ga content of the ternary layers were chosen to be x = 0.48 and y = 0.47, respectively, in order to obtain the same heterostructures identical to those grown lattice matched on InP as a reference. The surface morphology and the transport properties of Al(0.48)In(0.52)As/Ga(0.47)In(0.53)As high-electron mobility transistor structures were studied by atomic force microscopy and Hall measurements, respectively. Optical properties were investigated by low-temperature photoluminescence on quantum well structures. The use of the two step graded buffer layers resulted in three-dimensional layer grow th and inferior layer quality. In contrast, 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.