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Strain-induced enhancement of near-infrared absorption in Ge epitaxial layers grown on Si substrate
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Image of FIG. 1.
FIG. 1.

(a) Schematic illustration of deformation of Ge and Si crystals before and after cooling from a high-temperature to a low-temperature , (b) calculated results of strain as a function of in a -thick (001) Ge layer on a -thick (001) Si substrate for several different starting temperatures for cooling and (c) calculated result of strain in the Ge at RT (300 K) as a function of .

Image of FIG. 2.
FIG. 2.

Calculated results of C–HH and C–LH direct band-gap energies of biaxially strained (001) Ge as a function of the in-plane strain.

Image of FIG. 3.
FIG. 3.

(a) Typical XRD curves from the -thick Ge layer on Si (sample F: solid line) and bulk Ge (dashed line) and (b) in-plane strain by XRD as a function of starting temperature for cooling. The solid line shows the theoretical one.

Image of FIG. 4.
FIG. 4.

Typical PR spectra from samples E and F, which have the Ge layer with 0.20% tensile strain (bottom). Solid lines show the experimental spectra and dashed lines show the fitting results. The arrows show the C–LH and C–HH band-gap energies determined by the fitting of the spectra. Spectrum from the bulk Ge (middle) and theoretical relationship between the band-gap energies and the strain (top) are also shown.

Image of FIG. 5.
FIG. 5.

(a) Typical responsivity spectrum obtained for a Ge pin photodiode on a -Si wafer and (b) absorption coefficient of Ge layer on Si calculated using Eq. (8b). In (b), absorption coefficient for bulk Ge after Ref. 36 is also shown.

Image of FIG. 6.
FIG. 6.

Comparisons of absorption coefficient between experiment and theory for (a) bulk Ge and for (b) Ge layer on Si.

Image of FIG. 7.
FIG. 7.

Calculated responsivity spectra of photodiodes having -thick Ge layer with the tensile strain of 0–0.6%.


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Table I.

Summary of grown samples.

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Table II.

Fitting results of PR spectra.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Strain-induced enhancement of near-infrared absorption in Ge epitaxial layers grown on Si substrate