Nucleation of dislocations and twins within heteroepitaxial In1−xGaxAs layers grown on (001) InP under tensile stress conditions

Abstract

The defect structure, i.e. dislocations and twins, of MOVPE-grown In1−xGaxAs layers (x ≈︁ 0.5 to 0.73, tensile stress conditions) on (001)-oriented InP substrates is studied for layers of various thicknesses (t = 0.6 to 4.5 μm). Surface corrugations due to a preferred dislocation slip on (111) and (111) of the [110] zone and due to fracture parallel to [110] are observed and correlated to the internal defect structure. Tensile strain of the layers is mainly released by nucleation of perfect and partial dislocations at the free surface and not at the layer/substrate interface. Micron-deep grooves are formed where twins intersect the (001) surface. Twin growth proceeds by propagation of 90° Shockley partial dislocations from a surface-near region towards the layer/substrate interface, leaving a sessile 30° partial behind. It seems that Marée's conception of spontaneous half-loop nucleation at the free surface of a growing layer with critical thickness is favoured. Using this simple model, the demarcation line between the dislocation- and twin-free growth and that where these defects occur is calculated and determined experimentally. From simple crystallographic arguments (InGaAs belongs to the space group F443m) it is concluded that partial dislocations with excess In or Ga atoms in the core can be either generated or be moved more easily than dislocations with excess of As atoms.