Self-assembled growth in combination with prepatterning yields ordered lines of Ge islands on a planar Si (001) surface. The self-assembled Ge nanostructures are grown on top of a 15-period Si/SiGe superlattice, which is deposited on a prepatterned Si substrate. The pattern consists of 10 nm deep trenches with a period of 250 nm. The superlattice translates the surface modulation of the substrate into a strain-field modulation at the growth front of the superlattice. This strain field modulation provides the template for the ordered nucleation of self-assembled Ge islands. Our method gives rise to the long-range ordering of perfectly passivated nanostructures and can in principle be applied to any other strained material system.

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Room temperature distributed-feedback (DFB) laser operation is demonstrated with emission wavelengths ranging from 389 to 399 nm. Second-order DFB gratings were defined by electron beam lithography and reactive ion etching in the top GaN barrier layer of a GaInN/GaN double heterostructure grown by metalorganic vapor phase epitaxy. Our data allow a precise determination of the effective refractive index neff(λ) over the whole emission range. neff(λ) is compared with previously published values for GaN and GaInN.

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