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Indirect absorption in germanium quantum wells
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Figures

Image of FIG. 1.

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FIG. 1.

Experimental indirect absorption (solid) in Ge/SiGe quantum wells with Frova model (dashed) indirect absorption added to the modeled QCSE electroabsorption at two different electric fields where the two spectra become coincident at longer wavelengths. (a) Logarithmically scaled plot of the effective absorption coefficient (over the intrinsic region) and (b) a linearly scaled plot of the percent absorbed per pass (focussing on the QCSE portion) for the 60 QW sample.

Image of FIG. 2.

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FIG. 2.

Square root of the absorption coefficient showing (a) good agreement between the electric-field dependent model, Eq. (14), (dashed) and experimental data (solid) in comparison to (b) the one-phonon model, Eq. (13), (dashed) in the linear regime at two different electric fields. At most wavelengths of light, the two electric field curves (red and teal) are coincident.

Image of FIG. 3.

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FIG. 3.

Square root of indirect absorption in Ge/SiGe quantum wells with L-valley confinement energy included (dashed) compared with experimental data (solid) in the linear regime at two different electric fields. The resulting agreement with experimental data is worse than when L-valley confinement is excluded (as in Fig. 2(a)), especially at the wavelengths greater than 1.65μm. At most wavelengths of light, the two electric field curves (red and teal) are coincident.

Tables

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Table I.

Varshni Parameters for the relevant band gaps of Si and Ge. α is in units of 10−4 eV/K2, β is in K and E g, 0K is in eV.

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Table II.

Ge and Si elastic constants, spin orbit splitting and deformation potentials25

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Table III.

Ge and Si associated phonon energies (meV) and equivalent temperatures (K) calculated using kT, where k is Boltzmann's constant.

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/content/aip/journal/adva/1/3/10.1063/1.3646149
2011-09-21
2014-04-16

Abstract

Germanium has become a promising material for creating CMOS-compatible optoelectronic devices, such as modulators and detectors employing the Franz-Keldysh effect (FKE) or the quantum-confined Stark effect(QCSE), which meet strict energy and density requirements for future interconnects. To improve Ge-based modulator design, it is important to understand the contributions to the insertion loss (IL). With indirect absorption being the primary component of IL, we have experimentally determined the strength of this loss and compared it with theoretical models. For the first time, we have used the more sensitive photocurrent measurements for determining the effective absorption coefficient in our Ge/SiGe quantum well material employing QCSE. This measurement technique enables measurement of the absorption coefficient over four orders of magnitude. We find good agreement between our thin Gequantum wells and the bulk material parameters and theoretical models. Similar to bulk Ge, we find that the 27.7 meV LA phonon is dominant in these quantum confined structures and that the electroabsorption profile can be predicted using the model presented by Frova, Phys. Rev., 145 (1966).

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Scitation: Indirect absorption in germanium quantum wells
http://aip.metastore.ingenta.com/content/aip/journal/adva/1/3/10.1063/1.3646149
10.1063/1.3646149
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