Dependence of Threading Dislocation Density on Substrate Misorientation in In_0.15Ga_0.85As Grown on GaAs(100)

Abstract

The density and arrangement of dislocations in In_0.15Ga_0.85As grown on GaAs(100)) were determined by transmission electron microscopy as a function of misorientation toward (111)A, (111)B, and (110). Strained layer superlattices were used in all cases to reduce dislocation density. Layers grown on exact GaAs(100) exhibited a non-uniform threading dislocation dis- tribution whereby some areas had a high density (∼ 10⁹cm⁻²or higher) of dislocation tangles and other areas that we in between had a more uniform density (∼ 2 × 10⁷cm⁻²). The misorientated layers exhibited a uniform threading dislocation distribution with densities of ∼ 5 × 10⁶ cm⁻² for (100) misoriented towards (111)A, ∼ 1 × 10⁷cm⁻²towards (111)B, and ∼ 3 x 10⁷cm⁻² towards (110). The misfit dislocation network (dislocations located at the GaAs-InO_0.15Ga_0.85 As interface) formed orthogonal dislocation arrays in the case of exact (100) substrates and slightly non-ortho- gonal arrays in the case of misoriented substrates. These results are explained with the help of a general glide model of strain relaxation in which the exact (100) orientation has eight equally stressed glide systems which presumably activate during strain relaxation. With misoriented substrates the stress symmetry is broken and fewer glide systems experience the maximum stress, thus reducing the number of active dislocation systems. A small asymmetry in interfacial dis- location density was observed in all the cases where the linear dislocation density along the two (011) and (011) orthogonal directions differed by about 20%. This is explained by the preferred activation of (α-dislocations (high dislocation mobility) over β-dislocations (low dislocation mobility).