Scaling Hetero-Epitaxy from Layers to Three-Dimensional Crystals

Abstract

Quantum structures made from epitaxial semiconductor layers have revolutionized our understanding of low-dimensional systems and are used for ultrafast transistors, semiconductor lasers, and detectors. Strain induced by different lattice parameters and thermal properties offers additional degrees of freedom for tailoring materials, but often at the expense of dislocation generation, wafer bowing, and cracks. We eliminated these drawbacks by fast, low-temperature epitaxial growth of Ge and SiGe crystals onto micrometer-scale tall pillars etched into Si(001) substrates. Faceted crystals were shown to be strain- and defect-free by x-ray diffraction, electron microscopy, and defect etching. They formed space-filling arrays up to tens of micrometers in height by a mechanism of self-limited lateral growth. The mechanism is explained by reduced surface diffusion and flux shielding by nearest-neighbor crystals.

Photodetection in Hybrid Single-Layer Graphene/Fully Coherent Germanium Island Nanostructures Selectively Grown on Silicon Nanotip Patterns

“…For the growth of thick Ge layer, micro-meter sized patterning has been proposed to limit threading dislocation propagation and crack formation 8 . For the growth of nanometers sized Ge islands, the selective epitaxy using nanostructured Si with "seeds" (possibly surrounded by almost "inert" material, e.g.…”

Merging incompatible materials

“…The mechanism for the unusual mode of epitaxial growth, leading to the space-filling crystal arrays of Fig. 2, has been studied by theoretical modeling [10]. The main ingredients of the model are a negligibly small surface diffusion length and mutual flux shielding by neighboring crystals.…”

“…The only feasible way appears to be replacing a continuous layer by a dense array of individual crystal blocks [10]. But this has to happen spontaneously during crystal growth, since after cooling down it would be too late, as by then the layer would already have cracked!…”

“…Wafer bending and layer cracking are hence of major concern, especially when multiple-junction solar cells, high-brightness light emitting diodes and power electronic devices are to be grown onto cheap Si substrates. Here, I shall discuss another extreme case, namely an X-ray absorber monolithically integrated on a Si-CMOS (Complementary Metal Oxide Semiconductor) chip [10]. Because of its higher atomic number germanium is considered to be a viable candidate for replacing Si as the absorbing material.…”

Continuum modelling of semiconductor heteroepitaxy: an applied perspective

“…It must be pointed out that growth conditions far-from-equilibrium might lead to very different behaviours compared with thermodynamic expectations [66] and eventually induce other instabilities (see Ref. [54], and references therein).…”