Self-patterned Si surfaces as templates for Ge islands ordering

We propose a two-step process, which is based on substrate nano-patterning by means of growth instabilities in a first step and self-assembling of Ge dots on the top of surface instabilities in a second step. We used the instabilities that develop during the growth of Si(Ge) layers on both nominal and vicinal Si (111) or (001) surfaces. Depending on the growth conditions (Ge concentration, growth temperature, thickness), various growth instability regimes were observed: pure kinetic regime, kinetically activated strain-induced regime and pure strain-driven regime. In the case of Si/Si growth, kinetic instabilities developed at different growth temperatures depending on the surface orientation. The critical exponents describing evolution with time have been determined: amplitude A∼tβ and wavelength L∼tα. Experimental results show that each instability regime appears for a given growth temperature range that critically depends on the concentration of Ge. Evolution with time also depends on the Ge concentration. But in all cases, we evidence discrepancies between the experimental critical exponents and those predicted by classical modelling. We also give some examples of Ge dots self-organization on substrates nano-patterned (periodically undulated) by means of the different growth instabilities described above. In all cases, we observe Ge dots ordering along the substrate undulations due to step and/or strain effects. On kinetic instabilities (Si/Si(001) vicinal), Ge islands preferentially nucleate on step bunches. On SiGe(001) template layers, Ge dots nucleate on top of the SiGe undulations. In that case, strain gradients improved island ordering. The best ordering was achieved using View the MathML source off misoriented template layers as a result of almost perfect anisotropic morphology.