Crosshatch surface morphology and lateral oxidation in lattice-mismatched thin films

This thesis examines the mechanisms for strain relaxation during film growth and during post growth processing. First, enhanced strain relaxation growth templates by lateral wet oxidation are investigated for AlAs_0.80Sb_0.20 interlayers as a possible candidate for approaching the 6.1 Å lattice-parameter. The drawback for AlAs _1−xSb_x lateral wet oxidation is the precipitation of Sb metal at the oxide/semiconductor interfaces. The use of a water:methanol (1:0, 3:1, 1:1, and 1:3) wet oxidation mixture did reduce the oxidation rate and modify the Sb precipitate morphology, however the mixture did not prevent the Sb precipitates. Interlayer thickness was decreased to minimize the Sb precipitates, but at the reduced thickness h < 200Å, the diffusion of Ga into the AlAs_0.80Sb_0.20 interlayer prevented the oxidation. Doping the interlayers with Si or Te at 1018 cm −3 only altered the Sb precipitate morphology.; The second focus of this thesis is to characterize the dislocation structure in low lattice-mismatched films (ϵ < 0.02) by the observed surface crosshatch morphology. A model is investigated that incorporates two important elements: (i) strain relaxation due to dislocation glide in the layer that is associated with MD formation, referred to slip-step only (SSO), and (ii) lateral surface transport that eliminates surface steps, referred to slip-step eliminated (SSE). In Part I, A Monte Carlo simulation technique was applied to model dislocation nucleation. The surface stress and displacement profiles were calculated from the analytic elasticity solutions for single dislocations near a free surface. The results of the modeling in Part I predict that in both the SSO and SSE cases, the average amplitude of the surface undulations and their apparent wavelength both increase with increasing film relaxation and film thickness. In Part II, analytic elasticity solutions for truly periodic dislocations near a free surface are used. The results for films h ≥ 0.1 μm differ greatly from Part I. The SSE surface is atomically smooth and mesoscopically smooth while the SSO surface has well defined steps that produce a mesoscopically undulating surface. The conclusions of Part II are in agreement with atomic force microscopy (AFM) observations of crosshatch surface morphologies in In_0.25Ga_0.75As/GaAs samples.