ORIGIN AND FORMATION MECHANISM OF ELLIPTIC-SHAPED SURFACE DEFECT ON GAAS-LAYERS GROWN BY MOLECULAR-BEAM EPITAXY

We have investigated an elliptic-shaped surface defect on GaAs layers grown by molecular beam epitaxy on GaAs substrates. The presence of microscopic defects in GaAs substrates, which are revealed by AB etching, is not essential to the formation of surface defects of this type. They are convex to the epilayer surface and have one dislocation including a screw component near each of the centers. The results indicate that their origin is in the threading dislocations from GaAs substrates and that they are probably formed by spiral growth. We have also studied the effects of growth rate and substrate misorientation on the elliptic-shaped defects. As the growth rate increases, the sizes of the defects become smaller and they disappear at a rate of 4 mum/h. They are not formed on substrates oriented 2-degrees off the (100) towards the [110]. We briefly discuss these growth condition dependences concerned with spiral growth.