Growth Of Ge0 Research Articles

Band structure of germanium carbides for direct bandgap silicon photonics

Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge1−xCx (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III–V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

Large grain growth of Ge-rich Ge1−xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1−xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (∼800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ∼0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

Epitaxial growth of Ge0.975Sn0.025alloy films on Si(001) substrates by molecular beam epitaxy

Ge0.975Sn0.025 alloy films have been grown on Si(001) substrates by molecular beam epitaxy with high-quality Ge films as buffer layers.The alloys have high crystalline quality without Sn surface segregation, determined by double crystal X-ray diffraction and Rutherford backscattering spectra measurement. In addition, the Ge0.975Sn0.025 alloy has rather good thermal stability at 500 ℃, which makes it possible to be used in Si-based optoelectronic devices.

SiGe Epilayer Stress Relaxation: Quantitative Relationships Between Evolution of Surface Morphology and Misfit Dislocation Arrays

AbstractStress relaxation mechanisms have been investigated during growth of SiGe/Si heterostructures in a regime where misfit dislocations and surface morphological evolution strongly interact. Stress evolution was measured in real time using in situ wafer curvature measurements during molecular beam epitaxy of Ge0.3Si0.7 on Si (001). This real-time data has been combined with detailed analysis of the evolving surface morphology and misfit dislocation density using atomic force microscopy and transmission electron microscopy. Several distinct stages of microstructural evolution were observed during epitaxial growth of Ge0.3Si0.7alloys at intermediate temperatures (550°C) and relatively high deposition rate (0.9 Å/s). Initial planar, coherent growth was followed by pyramidal pit formation in the metastable wetting layer for 15nm thick films. Subsequent cooperative nucleation of island ridges occurs along <100> directions surrounding the pits. Dislocations are next introduced into the film abruptly at 50nm film thickness and relieve 40% of the film stress by 100nm of growth. Cross-hatch features aligned along the <110> directions accompany the introduction of misfit dislocations. As the dislocation density increases in the film, the coherent island/pit structures begin to disappear and the film morphology is dominated by the evolving cross-hatch. Implications for competitive and/or correlated relaxation of strain by misfit dislocations and surface morphology based upon this data will be discussed. This work demonstrates that combining real-time stress measurements with microscopy enables mechanistic and quantitative understanding of coupled relaxation modes in strained layer heteroepitaxy.

Novel Glide Planes in Epitaxially Grown Semiconductors

ABSTRACTThe accommodation of misfit stresses during heteroepitaxial growth of Ge0.85Si0.15 on Si(110) from In solution is studied by transmission electron microscopy. The regular misfit dislocation network forms at the interface and can be explained by glide of dislocations in a secondary a/2<110>{311} glide system. The occurrence of this secondary glide system is analyzed in terms of a mechanical equilibrium analysis that includes a frictional force due to a static Peierls barrier.

Evaluation of the Interface Structure During Stranski-Krastanov Growth of GE(SI) on Si (001)

ABSTRACTThe initial stages of heteroepitaxial growth of Ge0.85 Si0.15 on Si(001) grown from Bi solution (liquid phase epitaxy) are studid by transmission electron microscopy. Stranski-Krastanov growth is observed to take place. After growth of a pseudomorphic Ge0.85 Si0.15 layer of 4 monolayer thickness, islands form and grow pseudomorphically up to a thickness of 30 nm. Then first misfit dislocations form. The formation process of these dislocations is analyzed and discussed in terms of half loop nucleation at the surface and dislocation glide. Evidence for glide on (110) planes is put forward.

Role of strained layer superlattices in misfit dislocation reduction in growth of epitaxial Ge0.5Si0.5 alloys on Si(100) substrates

We investigate the role of strained layer superlattices in threading dislocation reduction in the growth of Ge0.5Si0.5 alloys on Si(100) substrates by molecular-beam epitaxy. Several superlattice structures are studied with zero, negative, and positive net strains with respect to a Ge0.5Si0.5 buffer layer. Control samples consisting of uniform strained layers are also grown for each superlattice structure. Transmission electron microscopy analysis of defect densities is found to be hampered by defect losses from thin foils, particularly in the plan view geometry. It is found that although strained interfaces are effective at deflecting threading dislocations into the interfacial plane, little surface threading dislocation density reduction is observed as a function of the presence of the superlattices for dislocation densities of the order 108 cm−2. This observation may be understood in terms of threading dislocation propagation at strained interfacial planes, and a simple predictive model is developed for defect interaction probabilities.