EPITAXIAL TILT OF PARTIALLY RELAXED INGAAS LAYERS GROWN ON (100) GAASSUBSTRATES

The structural properties of partially relaxed In(x)Ga1-xAs layers gro wn on (100) GaAs substrates have been investigated, using high-resolut ion X-ray diffraction, in order to better understand the mechanisms re sponsible for the relaxation of the mismatch strain. From symmetric [4 001 reflections recorded as functions of the azimuthal angle phi, the (100) InGaAs planes are found to be tilted with respect to the (100) G aAs substrate planes. The tilt magnitude is first seen to decrease the n to increase with layer thickness. The direction of the tilt changes from [01-1] to [00-1] in the range of thickness investigated. From [42 2] asymmetric reflections, the average in-plane lattice parameter, the indium composition as well as the percentage of relaxation can be mea sured. Our values for relaxation are in qualitative agreement with the Dodson and Tsao model of strain relaxation (Appl. Phys. Lett. 51, 171 0 (1987)). In addition, our data show an anisotropy in residual strain along [011] directions. This anisotropy increases with the amount of strain relieved and changes the crystal symmetry of the cell from tetr agonal to monoclinic. This monoclinic symmetry can be characterized by an angle beta that measures the angle between 90-degrees and the inne r angles of.the new crystallographic cell. As for the anisotropy in re sidual strain, beta increases with the amount of strain relieved. Corr elations between tilt magnitude and tilt direction with the formation of 60-degrees type dislocations are discussed.