Morphological evolution and strain relaxation of Ge islands grown on chemically oxidized Si(100) by molecular-beam epitaxy

Abstract

We have previously demonstrated that high-quality Ge can be grown on Si by the touchdown process, where chemically oxidized Si is exposed to a Ge molecular beam. The causes of strain relaxation in the Ge epilayer were also proposed and discussed. Herein, we present a detailed analysis on the morphological evolution and strain relaxation of nanoscale Ge islands on SiO2-covered Si in order to identify the mechanisms by which the high-quality epilayer forms. During the touchdown, the Ge seeds are anchored to the underlying Si. This immobility of Ge islands gives rise to a unique bimodal size distribution during coarsening. Three events are observed during coalescence: (1) merging of two small (<10nm) islands largely driven by surface diffusion, (2) merging of a small island and a big island (∼50nm), and (3) merging of two big islands. The coalescence of two small islands is characterized by the formation of twins or stacking faults at the two merging fronts. In contrast, no stacking fault or grain boundary results from the coalescence of large islands, indicating that their coalescence is favorable in achieving high-crystalline quality. For the Ge epilayer, the compressive strain exists mostly within 2nm from the heterojunction, resulting in a fully relaxed Ge epilayer. We attribute the relaxation to three mechanisms: (1) the strain at the junction pad decays below the critical limit within 2nm, a scale exactly comparable with the dimension of individual Ge–Si junction; (2) the remaining SiO2 serves as artificially introduced 60° dislocations; and (3) the intermixing between Ge and Si at the heterojunction reduces the effective lattice mismatch.

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

“…Ge covers this Si-dome by filling the interspace between the Si-dome and surrounding SiO 2 . This filling is believed to be the origin of the SF observed at the shoulder of the Si tip (see arrow in Figure 3a): the SF is formed owing to a defect on the SiO 2 surface [39][40] . It can be also noticed that the blue color at the edge of the Ge island fades out indicating a decrease 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 of Ge concentration, which is related to the formation of a Ge oxide layer on the Ge islands surface.…”

Size-induced enhanced magnetoelectric effect and multiferroicity in chromium oxide nanoclusters

“…The epitaxial relationship between the Cr 2 O 3 inclusions and the surrounding MgO matrix implies nominal in-plane compressive strains of À 7% along the c axis of the corundum structure, and of À 18% perpendicular to it (Methods). In epitaxial clusters, such a large lattice mismatch usually starts relaxing from the beginning of growth 22 . For t Cr ¼ 0.4 nm, photoluminescence spectra (Fig.…”

“…In the epitaxial growth of quantum dots, following either the Volmer-Weber or the Stranski-Krastanov modes, the introduction of dislocations 21 and the elastic relaxation at the dot edges 22 often yield an exponential relaxation of stress with increasing layer thickness. The epitaxial relationship between the Cr 2 O 3 inclusions and the surrounding MgO matrix implies nominal in-plane compressive strains of À 7% along the c axis of the corundum structure, and of À 18% perpendicular to it (Methods).…”

Effect of As Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

“…Different techniques of defect reduction such as substrate surface passivation, substrate patterning, thermal annealing, and growing Ge on a thin chemical oxide of Si by a ''touchdown process'' have been attempted. [6][7][8][9] The studies invariably have attributed the sudden change in aspect ratio that occurs at the onset of island evolution to strain relaxation and generation of defects. Only two studies relevant to Ge growth on (211)Si are available in the literature, with Ge growth achieved using MBE in both.…”