1:30 PM - EQ02.12.03
Composition and Strain Dependence of Phase Separation and Sn Surface Segregation in Ge/Ge1-xSnx Co-Axial Heterostructures
Michael Braun1,John Lentz1,Ishaa Bishnoi1,Andrew Meng2,Paul McIntyre1
Stanford University1,University of Pennsylvania2
Show Abstract
There has been significant interest in germanium-tin (GeSn) as a promising silicon-compatible group IV direct bandgap material for electronics and photonics. However, the maximum tin solubility in bulk GeSn solid solutions is only ~1 at% tin compared to the >10 at% tin compositions required for a direct bandgap material.1 The metastability of high tin content GeSn limits the thermal processing window for film deposition and post-growth annealing of epitaxial layers.2, 3 Previous reports on annealing results of strained germanium-tin epitaxial layers have shown undesirable surface segregation of tin. We report X-ray photoelectron spectroscopy results from in-situ and ex-situ annealing of core/shell Ge/Ge1-xSnx nanowire assemblies. Previously, we have shown the elastic compliance of small diameter Ge core nanowires in the core/shell structure produce largely strain-free Ge1-xSnx epilayers.4 Utilizing the variable strain control of this geometry, we investigate the annealing characteristics of the GeSn surface and native oxide for tin contents in the range of 2 at% - 12 at% in both air-exposed and oxide-free nanowires. For oxidized samples, we show the presence of a tin-rich oxide that exhibits a composition dependent temperature for thermal decomposition via in-situ annealing. By varying the shell thickness, we control the compressive strain in the shell enabling examination of phase separation behavior of the oxide-free, as-grown GeSn surface via ex-situ rapid thermal annealing and air-free transfer. Additionally, we have examined the annealing effects on bulk tin distribution and local surface structure via photoluminescence, X-ray diffraction, and high resolution transmission electron microscopy.
1M. Seifner, A. Dijkstra, J. Bernardi, A. Steiger-Thirsfield, M. Sistani, A. Lugstein, J. Haverkort, S. Barth, “Epitaxial Ge0.81Sn0.19 Nanowires for Nanoscale Mid-Infrared Emitters,” ACS Nano 13, 7 (2019), 8047-8054.
2S. Wu, L. Zhang, B. Son, Q. Chen, H. Zhou, C. Tan, “Insights into the Origins of Guided Microtrenches and Microholes/rings from Sn Segregation in Germanium-Tin Epilayers,” J. Phys. Chem. C 124 (2020), 20035-20045.
3W. Wang, L. Li, Q. Zhou, J. Pan, Z. Zhang, E. Tok, Y. Yeo, “Tin surface segregation, desorption, and island formation during post-growth annealing of strained epitaxial Ge1-xSnx layer on Ge(001) substrate,” Applied Surface Science 321 (2014), 240-244.
4A. Meng, M. Braun, Y. Wang, C. Fenrich, M. Xue, D. Diercks, B. Gorman, M. Richard, A. Marshall, W. Cai, J. Harris, P. McIntyre, “Coupling of coherent misfit strain and composition distributions in core-shell Ge/Ge1-xSnx nanowire light emitters,” Materials Today Nano 5 (2019), 100026.