Crystal defects in InGaAlAs layers grown on InP substrates by molecular beam epitaxy

InGaAlAs layers have been grown by molecular beam epitaxy on (001) oriented InP substrates. The crystal quality of the epilayers has been investigated by X-ray diffraction and electron microscopy techniques. It has been found that broad Bragg peaks, observed by double crystal diffractometry, are correlated to very high densities of dislocations and stacking faults, as evidenced by transmission electron microscopy. Using double crystal topography, it has been found that the best layers, whose Bragg peaks are as narrow as about 20 arc sec, contain virtually no dislocations, but sometimes a low concentration of stacking faults; scanning electron micrographs evidenced small growth hillocks corresponding to the stacking faults. The double crystal topographic contrast has been explained assuming a small difference of the lattice parameter in the hillocks with respect to the surrounding area. Finally, in the layers grown under large lattice mismatch conditions, misfit dislocations mainly located within the layers have been observed.