Compositional dependence of the direct and indirect band gaps in Ge1-ySny alloys from room temperature photoluminescence: Implications for the indirect to direct gap crossover in intrinsic and n-type materials

L. Jiang, J. D. Gallagher, C. L. Senaratne, T. Aoki, J. Mathews, John Kouvetakis, Jose Menendez

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67 Citations (Scopus)

Abstract

The compositional dependence of the lowest direct and indirect band gaps in Ge1-ySny alloys has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration yc at which the alloy becomes a direct gap semiconductor. For the direct gap, this is accomplished using a microscopic model that allows the determination of direct gap energies with meV accuracy. For the indirect gap, it is shown that current theoretical models are inadequate to describe the emission properties of systems with close indirect and direct transitions. Accordingly, an ad hoc procedure is used to extract the indirect gap energies from the data. For y < 0.1 the resulting direct gap compositional dependence is given by ΔE0 = -(3.57 ± 0.06)y (in eV). For the indirect gap, the corresponding expression is ΔEind = -(1.64 ± 0.10)y (in eV). If a quadratic function of composition is used to express the two transition energies over the entire compositional range 0 蠆 y 蠆 1, the quadratic (bowing) coefficients are found to be b0 = 2.46 ± 0.06 eV (for E0) and bind = 1.03 ± 0.11 eV (for Eind). These results imply a crossover concentration yc = , much lower than early theoretical predictions based on the virtual crystal approximation, but in better agreement with predictions based on large atomic supercells.

Original languageEnglish (US)
Article number115028
JournalSemiconductor Science and Technology
Volume29
Issue number11
DOIs
StatePublished - Nov 1 2014

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crossovers
Photoluminescence
Energy gap
photoluminescence
room temperature
Bending (forming)
Temperature
Semiconductor materials
Crystals
predictions
Chemical analysis
coefficients
approximation
crystals

Keywords

  • Alloys
  • GeSn
  • Photoluminescence

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials
  • Materials Chemistry
  • Condensed Matter Physics

Cite this

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title = "Compositional dependence of the direct and indirect band gaps in Ge1-ySny alloys from room temperature photoluminescence: Implications for the indirect to direct gap crossover in intrinsic and n-type materials",
abstract = "The compositional dependence of the lowest direct and indirect band gaps in Ge1-ySny alloys has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration yc at which the alloy becomes a direct gap semiconductor. For the direct gap, this is accomplished using a microscopic model that allows the determination of direct gap energies with meV accuracy. For the indirect gap, it is shown that current theoretical models are inadequate to describe the emission properties of systems with close indirect and direct transitions. Accordingly, an ad hoc procedure is used to extract the indirect gap energies from the data. For y < 0.1 the resulting direct gap compositional dependence is given by ΔE0 = -(3.57 ± 0.06)y (in eV). For the indirect gap, the corresponding expression is ΔEind = -(1.64 ± 0.10)y (in eV). If a quadratic function of composition is used to express the two transition energies over the entire compositional range 0 蠆 y 蠆 1, the quadratic (bowing) coefficients are found to be b0 = 2.46 ± 0.06 eV (for E0) and bind = 1.03 ± 0.11 eV (for Eind). These results imply a crossover concentration yc = , much lower than early theoretical predictions based on the virtual crystal approximation, but in better agreement with predictions based on large atomic supercells.",
keywords = "Alloys, GeSn, Photoluminescence",
author = "L. Jiang and Gallagher, {J. D.} and Senaratne, {C. L.} and T. Aoki and J. Mathews and John Kouvetakis and Jose Menendez",
year = "2014",
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day = "1",
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TY - JOUR

T1 - Compositional dependence of the direct and indirect band gaps in Ge1-ySny alloys from room temperature photoluminescence

T2 - Implications for the indirect to direct gap crossover in intrinsic and n-type materials

AU - Jiang, L.

AU - Gallagher, J. D.

AU - Senaratne, C. L.

AU - Aoki, T.

AU - Mathews, J.

AU - Kouvetakis, John

AU - Menendez, Jose

PY - 2014/11/1

Y1 - 2014/11/1

N2 - The compositional dependence of the lowest direct and indirect band gaps in Ge1-ySny alloys has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration yc at which the alloy becomes a direct gap semiconductor. For the direct gap, this is accomplished using a microscopic model that allows the determination of direct gap energies with meV accuracy. For the indirect gap, it is shown that current theoretical models are inadequate to describe the emission properties of systems with close indirect and direct transitions. Accordingly, an ad hoc procedure is used to extract the indirect gap energies from the data. For y < 0.1 the resulting direct gap compositional dependence is given by ΔE0 = -(3.57 ± 0.06)y (in eV). For the indirect gap, the corresponding expression is ΔEind = -(1.64 ± 0.10)y (in eV). If a quadratic function of composition is used to express the two transition energies over the entire compositional range 0 蠆 y 蠆 1, the quadratic (bowing) coefficients are found to be b0 = 2.46 ± 0.06 eV (for E0) and bind = 1.03 ± 0.11 eV (for Eind). These results imply a crossover concentration yc = , much lower than early theoretical predictions based on the virtual crystal approximation, but in better agreement with predictions based on large atomic supercells.

AB - The compositional dependence of the lowest direct and indirect band gaps in Ge1-ySny alloys has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration yc at which the alloy becomes a direct gap semiconductor. For the direct gap, this is accomplished using a microscopic model that allows the determination of direct gap energies with meV accuracy. For the indirect gap, it is shown that current theoretical models are inadequate to describe the emission properties of systems with close indirect and direct transitions. Accordingly, an ad hoc procedure is used to extract the indirect gap energies from the data. For y < 0.1 the resulting direct gap compositional dependence is given by ΔE0 = -(3.57 ± 0.06)y (in eV). For the indirect gap, the corresponding expression is ΔEind = -(1.64 ± 0.10)y (in eV). If a quadratic function of composition is used to express the two transition energies over the entire compositional range 0 蠆 y 蠆 1, the quadratic (bowing) coefficients are found to be b0 = 2.46 ± 0.06 eV (for E0) and bind = 1.03 ± 0.11 eV (for Eind). These results imply a crossover concentration yc = , much lower than early theoretical predictions based on the virtual crystal approximation, but in better agreement with predictions based on large atomic supercells.

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