STRAIN RELIEF IN LINEARLY GRADED COMPOSITION BUFFER LAYERS - A DESIGNSCHEME TO GROW DISLOCATION-FREE (LESS-THAN-10(5) CM(-2)) AND UNSTRAINED EPILAYERS

The strain relaxation in linearly graded composition InGaAs layers gro wn on (001) GaAs substrates by molecular beam epitaxy is studied by tr ansmission electron microscopy (TEM) and double crystal x-ray diffract ion (DCXRD). The dislocation distribution in these layers does not coi ncide with the predicted equilibrium dislocation distribution [J. Ters off, Appl. Phys. Lett. 62, 693 (1993)]. The dislocation density in the dislocation-rich layer thickness is slightly smaller than the equilib rium density. The thickness of the dislocation-rich region is differen t in the [110] and [110] directions. A good correspondence exists betw een the TEM and DCXRD strain measurements. The dislocation distributio n observed by TEM has made it possible to design a scheme to grow disl ocation-free and unstrained top layers on Linearly graded composition buffer layers. (C) 1993 American Institute of Physics.