THE MORPHOLOGY AND ASYMMETRIC STRAIN RELIEF BEHAVIOR OF INAS FILMS ON GAAS (110) GROWN BY MOLECULAR-BEAM EPITAXY

30, 60 and 400 angstrom thick InAs layers on GaAs (110) grown by MBE were studied using both TEM and X-ray diffraction techniques. Two different strain relief mechanisms, directly associated with (110) surface geometry, were observed in the two orthogonal directions [110BAR] and [001]. In the [110BAR] direction, the strain relief was via the nucleation of a regular array of Lomer type dislocations which have line direction u = [001] and Burgers vector b = 1/2a[110BAR], whereas the relief in the [001] direction was via the generation of 60-degrees type dislocations with u = [110BAR] and b = 1/2a[101] and 1/2[011]. The density of the latter was film thickness dependent. As a consequence, the overall strain relief of the InAs layers was thickness dependent and asymmetric in the thinner layers. The 60-degrees type dislocations also give rise to local tilt about the [110BAR] direction with large overall tilt in the thicker layer (400 angstrom).