Structural characterization of lattice matched Al_xIn _1-xAs/InP and Ga_yIn_1-yAs/InP heterostructures by transmission electron microscopy and high-resolution x-ray diffraction

In this work we report on transmission electron microscopy and high-resolution x-ray diffractometry studies of lattice matched Al _xIn_1-xAs/InP and Ga_yIn_1-yAs/InP epilayers grown by molecular beam epitaxy on InP(100) substrates. High-resolution and diffraction contrast electron microscopy measurements show the presence of different contrast zones in the epilayers. The analysis of high-resolution x-ray diffraction measurements and computer simulations ascribe these zones to the presence of a compositional gradient in the epilayers. A comparison among investigated samples grown under slightly different growth conditions combined with an analysis of the crystal defects is presented. Growth-induced small variations in the chemical composition of the epilayer can produce differences in the structural quality of the epitaxial layer. Finally, a few monolayers thick and highly strained film of InAsP, is observed in all investigated samples at the substrate/epilayer interface. The formation of this interface layer is explained by the exchange of As and P during exposure of the InP surface to As₄ before the growth.