Structural and electrical evaluation of the influence of carbon delta layers for defect reduction on epitaxial growth of thin, relaxed germanium layers on silicon substrates
Final Report Abstract
The monolithic integration of germanium into the well-established silicon technology is cutting edge research since it paves the way to integrate optoelectronics, quantum computing and 2D materials in the world of nanoelectronics. The main challenge is to combine the growth of thin germanium layers with a low density of defects in the surface region, using a process that is suitable to implement in silicon technology. Framed by these requirements, a process has been developed in the present dissertation that is based on the integration of carbon delta-layers as defect filter layers. Using a two-level defect filter structure of this kind, the density of threading dislocations was reduced by a factor of 1.4 compared to reference samples grown without any filter layer. The working principle of the defect filter layers is that of a strained-layer superlattice in which the lattice mismatch is generated by carbon delta-layers which are buried in the germanium layer. Investigations of carbon adatoms on germanium surfaces have shown a thermodynamic preference to form carbon clusters. This can be kinetically hindered by low substrate temperature yielding shallow lattice incorporation of carbon. The tension of the germanium lattice was proven by X-ray diffraction and nano-beam-electron-diffraction and also quantified. Superlattices strained by this technique start to relax plastically in a temperature range of 430◦C ≤ T ≤ 500◦C as proven by temperature-dependent analyzation techniques. The plastic relaxation of the upper layer comprised the bending of a threading dislocation and forming an edge segment in the carbon delta-layer. This process was observed live by in situ heating transmission electron microscopy. Compared to unfiltered reference samples, samples with a single defect filter layer showed no reduced density of threading dislocations but multiple defect filter layers have proven to be effective in defect reduction. A germanium layer of 1,1μm thickness with two levels of submonolayer carbon defect filter layers was measured to have a defect density of 4 · 108 cm^−2 which is 1.4 times less than a reference sample without filter layer. Carbon-delta-layer based strained-layer superlattices have proven capable of reducing the density of defects in epitaxially grown Ge/Si(001) layers. The process described in this dissertation makes it possible to grow thin layers with reduced defect density while having a low thermal load. In conclusion, this process is suitable for monolithic integration of thin epitaxial Ge layers into silicon technologies.
Publications
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Highly boron-doped germanium layers on Si(001) grown by carbon-mediated epitaxy. Semicond. Sci. Technol. 33 (2018) 104006
Y. Barnscheidt, J. Schmidt, G. Wetzel, D. Tetzlaff, T. F. Wietler and H.J. Osten
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Carbon-Modified-Germanium-Epitaxy: Filtering Threading Dislocations with Carbon Delta Layers. ECS Transactions. 93 (2019) 67–70
Y. Barnscheidt and H.J. Osten
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Grazing-incidence X-ray diffraction investigation of the coincidence site lattice of the Ge/Si(001) system. Journal of Applied Crystallography. 53 (2020)
Y. Barnscheidt, J. Schmidt and H.J. Osten
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Paving the way to dislocation reduction in Ge/Si(001) heteroepitaxy using C-based strained layer superlattices. Journal of Applied Physics. 128 (2020) 95703
Y. Barnscheidt, M. Franck and H.J. Osten
