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New experimental evidence for nature of the band gap of GeSn alloys (Conference Presentation)
Author(s): Timothy D. Eales; Igor P. Marko; Seyed A. Ghetmiri; Wei Du; Yiyin Zhou; Shui-Qing Yu; Joe Margetis; John Tolle; Stefan Schulz; Edmond O’Halloran; Eoin P. O'Reilly; Stephen J. Sweeney
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Paper Abstract

To harness the advanced fabrication capabilities and high yields of the electronics industry for photonics, monolithic growth and CMOS compatibility are required. One promising candidate which fulfils these conditions is GeSn. Introducing Sn lowers the energy of the direct Γ valley relative to the indirect L valley. The movement of the conduction band valleys with Sn concentration is critical for the design of efficient devices; however, a large discrepancy exists in the literature for the Sn concentration at which GeSn becomes a direct band gap. We investigate the bandgap character of GeSn using hydrostatic pressure which reversibility modifies the bandstructure. In this work we determine the movement of the band-edge under pressure using photocurrent measurements. For a pure Ge sample, the movement of the band-edge is dominated by the indirect L valley with a measured pressure coefficient of 4.26±0.05 meV/kbar. With increasing Sn concentration there is evidence of band mixing effects, with values of 9.4±0.3 meV/kbar and 11.1±0.2 meV/kbar measured for 6% and 8% Sn samples. For a 10% Sn sample the pressure coefficient of 13±0.5 meV/kbar is close to the movement of the direct bandgap of Ge, indicating predominately direct Γ-like character for this GeSn alloy. This further suggests a gradual transition from indirect to direct like behaviour in the alloy as also evidenced from theoretical calculations. The implications of this in terms of optimising device performance will be discussed in further detail at the conference.

Paper Details

Date Published: 28 April 2017
PDF: 1 pages
Proc. SPIE 10108, Silicon Photonics XII, 101080F (28 April 2017); doi: 10.1117/12.2252724
Show Author Affiliations
Timothy D. Eales, University of Surrey (United Kingdom)
Igor P. Marko, Univ. of Surrey (United Kingdom)
Seyed A. Ghetmiri, Univ. of Arkansas (United States)
Wei Du, Univ. of Arkansas (United States)
Yiyin Zhou, Univ. of Arkansas (United States)
Shui-Qing Yu, Univ. of Arkansas (United States)
Joe Margetis, ASM America Inc. (United States)
John Tolle, ASM America Inc. (United States)
Stefan Schulz, Tyndall National Institute (Ireland)
Edmond O’Halloran, Tyndall National Institute (Ireland)
Eoin P. O'Reilly, Tyndall National Institute (Ireland)
Stephen J. Sweeney, Univ. of Surrey (United Kingdom)


Published in SPIE Proceedings Vol. 10108:
Silicon Photonics XII
Graham T. Reed; Andrew P. Knights, Editor(s)

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