Research ArticleENGINEERING

Breaking the absorption limit of Si toward SWIR wavelength range via strain engineering

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Science Advances  29 Jul 2020:
Vol. 6, no. 31, eabb0576
DOI: 10.1126/sciadv.abb0576
  • Fig. 1 Fabrication of 6 × 6 Si NM array devices for strain-controlled stretchable PD.

    (A) Schematic illustration of device fabrication. RIE, reactive ion etching. (B) Photograph of a fabricated device on PI-coated SiO2/Si substrate and corresponding magnified view of device sections. (C) SEM images of convex (top) and concave (bottom) hemispherical shape of bulged PI film containing a 6 × 6 Si-NM PD array. Scale bars, 0.5 mm.

  • Fig. 2 Strain and photodetection characteristics of single MSM device fabricated on 20 μm by 20 μm–sized 10-nm-thick Si NM and theoretical calculation of electronic band structure.

    (A) Raman spectra of 10-nm-thick Si NM sample recorded with increasing pressure. The spectra show the Raman scattering intensity enhancement and peak position shift toward the lower wave number side with increasing pressure. a.u., arbitrary units. (B) Maximum applied biaxial strain value in Si NMs of different thicknesses via the bulging process just before fracture. The inset shows the Si NM before (bottom left) and after fracture (top right). (C) Strain-dependent electronic band structure of 10-nm-thick Si NM with an applied biaxial strain of up to 4%. (D) Schematic representation of atomic arrangements of ~10-nm-thick Si NM used in theoretical calculation. (E) Bandgap values of different transitions extracted from the calculated energy band diagram for 10-nm-thick Si NM sample subjected to increasing biaxial tensile strain.

  • Fig. 3 Strain-induced photoresponse and imaging characteristics of fabricated PD array.

    (A) Photograph of the 6 × 6 Si-NM PD array device mounted on bulge test setup with increasing pressure (scale bars, 1 mm). Photo credit: Ajit K. Katiyar, Yonsei University. (B) Strain-dependent transient photoresponse of single 10-nm-thick Si NM device measured under incident light of different wavelengths, from 405 to 1550 nm. The plots reveal the photosensing capability of the 10-nm-thick Si NM device beyond the Si photoabsorption wavelength range (400 to 1100 nm) under the applied strain. A clear on/off in photoresponse can be noticed under the 1550-nm light above the 3.5% applied biaxial strain. (C) Digital photographs of the Si-NM PD array device captured during imaging with lights of various wavelengths (scale bars, 3 mm). Photo credit: Ajit K. Katiyar, Yonsei University. (D) Corresponding photocurrent mapping images recorded under incident light of different wavelengths.

  • Fig. 4 Overview of optical imaging system and object images obtained from 6 × 6 Si-NM PD array under increasing strain.

    (A) Schematic illustration of the overall imaging system and optical setup used for imaging of the letter Y containing a collimated light source, shadow mask, and device array. (B) Enlarged view of the schematic representation for imaging of Y alphabet. (C) Photocurrent mapping images of a representative letter recorded under incident light of 1310 nm with increasing straining pressure. An increase in photocurrent with increase in applied pressure is evident, which is a consequence of the increased strain in each Si NM pixel. (D) Photographic images and corresponding acquired mapping images of the fabricated PD pixel arrays under convex hemispherical geometry. The laser is projected at an incident angle of ~20° from the normal at both sides of the PD arrays. Photo credit: Ajit K. Katiyar, Yonsei University.

  • Fig. 5 Photoresponse obtained from 6 × 6 Si NM PD array under concave architecture.

    (A) Photocurrent mapping images of a representative letter recorded under incident light of 1310 nm with increasing straining pressure in concave geometry. (B) Curvature of concave surface PD pixel under increased straining pressure. (C) Photocurrent mapping image recorded with a light beam focused by a planoconvex lens onto the PD matrix system subjected to the increasing surface curvature. (D) Schematic representation of the photoresponse measurement of alphabet character I focused with planoconvex lens under flat and curved surface of PD matrix. (E) Representative mapping images of alphabet character I recorded with PD matrix under flat and concave architecture. Insets schematically show the light intensity distribution on the PD matrix surface under planar and curved geometry and corresponding photocurrent mapping image in 2D representation.

Supplementary Materials

  • Supplementary Materials

    Breaking the absorption limit of Si toward SWIR wavelength range via strain engineering

    Ajit K. Katiyar, Kean You Thai, Won Seok Yun, JaeDong Lee, Jong-Hyun Ahn

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