(Invited) Epitaxial Growth of GeSn Layers on (001), (110), and (111) Si and Ge Substrates
Ge1-xSnx epitaxial growth on (110) and (111) substrates
We examined the epitaxial growth of Ge1-xSnx layers on (110) and (111) Ge substrates [5-8]. We found that introducing Sn with a content as low as 2% into Ge is effective to reduce staking faults and twin defects in Ge epitaxial layers on (110) substrates even with the low-temperature growth of 150°C. We also found that the strain relaxation of Ge1-xSnxon (110) and (111) substrates takes place preferentially with a smaller Sn content than that grown on (001) substrate, that is attributed to the surface orientation dependence of the elastic modulus of epitaxial layers.
The Sn incorporation into Ge also improves on the crystalline quality of epitaxial layers prepared with low-temperature MBE on Si(110) substrate . Formation of twin defects in Ge epitaxial layers on Si(110) can be drastically suppressed by the incorporation of Sn with a content of 2%. The propagation of misfit dislocations can be effectively enhanced during the post deposition annealing by suppressing the formation of twin defects.
Local growth of Ge1-xSnx epitaxial layers
We examined the formation of locally strained Ge1-xSnx/Ge fine structure and characterized the microscopic local strain structures by using X-ray microdiffraction method . The local growth of Ge1-xSnx with a Sn content of 6.5% on fine-structure-patterned-Ge is achieved with low-temperature MBE. The concentration of local stress in embedded Ge1-xSnx layer causes the degradation of crystallinity with tilting of the lattice plane and Sn precipitation. We can directly measure the individual local strain in Ge sandwiched with Ge1-xSnxlocal stressor by microdiffraction. We demonstrate increasing in the in-plane strain with shrinking the Ge width and increasing the Sn content. The maximum in-plane compressive strain is estimated to be 1.4% for a width of 25 nm.
In the presentation, we will also talk about some electronic and optical properties of high Sn content Ge1-xSnx epitaxial layers and introduce some recent achievement in the epitaxial growth of Sn-related ternary alloys such as Ge1-x-ySixSny.
This work was partially supported by a Grant-in-Aid for Specially Promoted Research of MEXT, the JSPS through the FIRST Program, and the ALCA program from JST in Japan. The microdiffraction measurement was performed at SPring-8 with the approval of general proposals (No. 2013A1682 and No. 2013B1779/BL13XU).
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