MOLECULAR-BEAM EPITAXY OF AL0.48IN0.52AS GA0.47IN0.53AS HETEROSTRUCTURES ON METAMORPHIC ALXGAYIN1-X-YAS BUFFER LAYERS/

Ternary AlxIn1-xAs/GayIn1-yAs heterostructures with a lattice mismatch up to 4% are grown on GaAs by molecular beam epitaxy. Two buffer laye r concepts to compensate the lattice misfit between the AlxIn1-xAs/Gay In1-yAs layers and the GaAs substrate using the quaternary AlxGayIn1-y As in a linear graded and two-step graded fashion, respectively, are p resented. 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 he terostructures identical to those grown lattice matched on InP as a re ference. The surface morphology and the transport properties of Al0.48 In0.52As/Ga0.47In0.53As high-electron mobility transistor structures w ere studied by atomic force microscopy and Hall measurements, respecti vely. Optical properties were investigated by low-temperature photulum inescence on quantum well structures. The use of the two step graded b uffer layers resulted in three-dimensional layer growth and inferior l ayer quality. In contrast, the linear graded buffer approach was found to result in superior heterostructure properties due to the two-dimen sional growth mode during the whole growth process resulting in the ty pical cross-hatched surface morphology.