Cation diffusion in InP/In0.53Ga0.47As superlattices: strain build-up and relaxation

InP and In_0.53Ga_0.47As are lattice matched and can form superlattices that are free of crystalline defects. Zn indiffusion enhances the diffusion of cations while leaving the anions unaffected; the resultant In_1-xGa_xP/In_1-xGa_xAs superlattices are strained. Since the as-grown specimens are pseudomorphic, any defects observed after Zn diffusion must be attributed to strain relaxation. Studies of the post-growth strain build-up and relaxation in this novel system suggest a new strain relief mechanism for buried strained layers of face-centred-cubic (fcc) structures. The signature defect of the proposed mechanism is a microtwin along a {111} plane spanning the buried strained layer and terminating at both interfaces with partial dislocations of 1/6<112> type. Energy analysis indicates that this new partial-dislocation strain relief mechanism is more effective than the conventional 60† perfect-dislocation mechanism for relieving the in-plane strain in buried strained layers. Therefore, the proposed mechanism is an energetically favourable relaxation channel and limits the useful thicknesses of strained layers in electronic and optoelectronic devices.