### Abstract

Epitaxial Ge layers on a Si substrate experience a tensile biaxial stress due to the difference between the thermal expansion coefficients of the Ge epilayer and the Si substrate, which can be measured using asymmetric X-ray diffraction reciprocal space maps. This stress depends on temperature and affects the band structure, interband critical points, and optical spectra. This manuscripts reports careful measurements of the temperature dependence of the dielectric function and the interband critical point parameters of bulk Ge and Ge epilayers on Si using spectroscopic ellipsometry from 80 to 780K and from 0.8 to 6.5eV. The authors find a temperature-dependent redshift of the E _{1} and E _{1} +δ_{1} critical points in Ge on Si (relative to bulk Ge). This redshift can be described well with a model based on thermal expansion coefficients, continuum elasticity theory, and the deformation potential theory for interband transitions. The interband transitions leading to E0' and E _{2} critical points have lower symmetry and therefore are not affected by the stress.

Original language | English (US) |
---|---|

Journal | Applied Surface Science |

DOIs | |

State | Accepted/In press - Jul 27 2016 |

### Fingerprint

### Keywords

- Critical points
- Dielectric function
- Germanium
- Spectroscopic ellipsometry
- Strain
- Temperature dependence

### ASJC Scopus subject areas

- Surfaces, Coatings and Films

### Cite this

*Applied Surface Science*. https://doi.org/10.1016/j.apsusc.2016.09.019

**Temperature dependence of the interband critical points of bulk Ge and strained Ge on Si.** / Fernando, Nalin S.; Nunley, T. Nathan; Ghosh, Ayana; Nelson, Cayla M.; Cooke, Jacqueline A.; Medina, Amber A.; Zollner, Stefan; Xu, Chi; Menendez, Jose; Kouvetakis, John.

Research output: Contribution to journal › Article

*Applied Surface Science*. https://doi.org/10.1016/j.apsusc.2016.09.019

}

TY - JOUR

T1 - Temperature dependence of the interband critical points of bulk Ge and strained Ge on Si

AU - Fernando, Nalin S.

AU - Nunley, T. Nathan

AU - Ghosh, Ayana

AU - Nelson, Cayla M.

AU - Cooke, Jacqueline A.

AU - Medina, Amber A.

AU - Zollner, Stefan

AU - Xu, Chi

AU - Menendez, Jose

AU - Kouvetakis, John

PY - 2016/7/27

Y1 - 2016/7/27

N2 - Epitaxial Ge layers on a Si substrate experience a tensile biaxial stress due to the difference between the thermal expansion coefficients of the Ge epilayer and the Si substrate, which can be measured using asymmetric X-ray diffraction reciprocal space maps. This stress depends on temperature and affects the band structure, interband critical points, and optical spectra. This manuscripts reports careful measurements of the temperature dependence of the dielectric function and the interband critical point parameters of bulk Ge and Ge epilayers on Si using spectroscopic ellipsometry from 80 to 780K and from 0.8 to 6.5eV. The authors find a temperature-dependent redshift of the E 1 and E 1 +δ1 critical points in Ge on Si (relative to bulk Ge). This redshift can be described well with a model based on thermal expansion coefficients, continuum elasticity theory, and the deformation potential theory for interband transitions. The interband transitions leading to E0' and E 2 critical points have lower symmetry and therefore are not affected by the stress.

AB - Epitaxial Ge layers on a Si substrate experience a tensile biaxial stress due to the difference between the thermal expansion coefficients of the Ge epilayer and the Si substrate, which can be measured using asymmetric X-ray diffraction reciprocal space maps. This stress depends on temperature and affects the band structure, interband critical points, and optical spectra. This manuscripts reports careful measurements of the temperature dependence of the dielectric function and the interband critical point parameters of bulk Ge and Ge epilayers on Si using spectroscopic ellipsometry from 80 to 780K and from 0.8 to 6.5eV. The authors find a temperature-dependent redshift of the E 1 and E 1 +δ1 critical points in Ge on Si (relative to bulk Ge). This redshift can be described well with a model based on thermal expansion coefficients, continuum elasticity theory, and the deformation potential theory for interband transitions. The interband transitions leading to E0' and E 2 critical points have lower symmetry and therefore are not affected by the stress.

KW - Critical points

KW - Dielectric function

KW - Germanium

KW - Spectroscopic ellipsometry

KW - Strain

KW - Temperature dependence

UR - http://www.scopus.com/inward/record.url?scp=85007004344&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85007004344&partnerID=8YFLogxK

U2 - 10.1016/j.apsusc.2016.09.019

DO - 10.1016/j.apsusc.2016.09.019

M3 - Article

AN - SCOPUS:85007004344

JO - Applied Surface Science

JF - Applied Surface Science

SN - 0169-4332

ER -