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Nanoheteroepitaxy has recently been proposed as a technique for significantly extending the thickness of pseudomorphic growth in mismatched heterostructures. This letter reports the experimental application of nanoheteroepitaxy for the growth of GaN on patterned 〈111〉 oriented silicon-on-insulator substrates by organometallic vapor phase epitaxy. Transmission electron microscopy reveals that the defect concentration decays rapidly away from the heterointerface as predicted by nanoheteroepitaxy theory. The melting point of the nanoscale islands is found to be significantly reduced, enhancing substrate compliance and further reducing the strain energy in the GaN epitaxial layer.

Interference effects between two coherent laser beams have long been used to create simple grating patterns in photoresist. With the addition of multiple exposures with variations in period, phase, and orientation, in the same level of photoresist, highly complex one- and two-dimensional patterns of potential interest for device application are demonstrated. The spatial scale of the lines forming these patterns is ∼1/4 of the writing wavelength λ (period to λ/2 and line to space ratio of 1:1) and is in the extreme submicron range, ∼0.1 μm, for readily available laser sources, such as an Ar+-ion laser operating at 364 nm. Importantly, the depth-of-focus for these pairwise exposures is unlimited on the scale of typical semiconductor device topographies and large area, uniform exposures to scales much larger than projected integrated circuit die sizes (e.g., to 30×30 cm2) are easily achieved. These patterns are closely related to moiré interference patterns; relationships are illustrated. Diffractive readout is shown to be a powerful and intuitive technique for monitoring these structures. Additional flexibility in pattern fabrication is provided with conventional lithography to define areas on a larger scale and by the use of aperture and phase masks to isolate areas. An example is the fabrication of an interdigitated structure with submicron spaces over a large area.

Nanoheteroepitaxy is a fundamentally new epitaxial approach that utilizes three-dimensional stress relief mechanisms available to nanoscale heterostructures to eliminate defects provided the island diameter is below a critical value 2lc. Analysis shows that 2lc∼(15–30)× the critical thickness hc. In the case of GaAs on Si (∼4% misfit), 2lc∼40 nm. In material systems such as GaN on Si (∼20% misfit), where the misfit is much larger and interfacial defects are unavoidable, the nanoheteroepitaxial structure is shown to reduce the formation and propagation of threading defects. Nanostructured substrate parameters that impact growth are discussed and interferometric lithography is introduced as a method for fabrication of large-area substrates for nanoheteroepitaxy. Si nanoisland diameters as small as 20 nm are demonstrated. Scanning and transmission electron microscopy data of GaN grown on Si (via organometallic vapor phase epitaxy) shows reduced threading defects in nanostructured samples compared to growth on planar substrates. Photoluminescence intensity data of nanostructured samples is enhanced by ∼100× as compared to planar-growth samples.