High resolution electron microscope analysis of lattice distortions and Insegregation in highly strained In0.35Ga0.65As coherent islands grown on GaAs (001)

Lattice distortions in three-dimensional coherent In0.35Ga0.65As islands gr own by molecular beam epitaxy at 510 degrees C on GaAs have been imaged by high resolution electron microscopy. The strain fields are determined from the corresponding digital images, either by direct measurement of the latti ce distortions or by combining real space and Fourier space information, wi th an uncertainty Delta epsilon=2 x 10(-3). The strain fields are also simu lated through finite-element calculations, taking into account the strain r elaxation due to the low thickness of the electron-transparent specimens. T he significant differences found between experimental and calculated strain fields are attributed to In segregation within the islands. Bidimensional compositional maps are then established showing that the In concentration i n the central part of the islands (up to similar to 50%) is significantly h igher than the nominal concentration (35%), whereas it is lower (down to si milar to 20%) at the edges of the islands. (C) 1999 American Institute of P hysics. [S0021-8979(99)06416-6].