A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited

Abstract

Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light.

Germanium-on-Nothing for Epitaxial Liftoff of GaAs Solar Cells

“…The cylindrical pores arranged in square arrays are patterned on a Ge substrate using nanoimprint lithography (NIL) and reactive ion etching for well-ordered and sub-micron-scaled pore fabrication, as we demonstrated in SON technology. 23 The cylindrical Ge pores are then annealed in hydrogen for reorganization into the GON structure. As illustrated in Figures 1F and 1G, the final shape of the GON structure can be varied by the initial morphology of the Ge pores.…”

PCA-based sub-surface structure and defect analysis for germanium-on-nothing using nanoscale surface topography

“…The individual cavities formed in the initial annealing stage are utilized as photonic crystals 9 , the merged cavities are utilized as absolute pressure sensors by deflection of the membrane 10 – 12 and flow channels for microcapillaries and resonators 13 – 15 . Other applications that value the cavity’s peripherals remove and handle the self-assembled membrane in a separate manner to fabricate solar cells 4 , 16 , 17 and semitransparent silicon films 18 . Appropriate employment of these devices from SON and GON structures require a precise degree of cavity saturation, with specific morphologies of both surface and sub-surface structures.…”

“…This work uses surface-fitted polynomial coefficients as the extracted features of the surface topography pattern, and will focus on GON structures. Annealed with the same initial pattern, GON and SON structures are known to temporally transform in a similar fashion 4 , 18 . Namely, annealing a 2-D lattice patterned initial structure yields either spherical voids or plate-shaped voids depending on the diameter, pitch, and depth of the initial pattern.…”

PCA-Based Analysis Applied to Germanium-On-Nothing: Revealing Buried Sub-Surface Structures and Analyzing Defects From Nanoscale Surface Topography

“…The individual cavities formed in the initial annealing are utilized as photonic crystals 8 , the merged cavities are utilized as absolute pressure sensors by deflection of the membrane [9][10][11] , and flow channels as microcapillaries and resonators [12][13][14] . Other applications that value the cavity's peripherals remove and handle the self-assembled membrane in a separate manner to fabricate solar cells 4,15,16 and semitransparent silicon films 17 . Appropriate employment of these devices from SON and GON structures require a precise degree of cavity saturation, with specific morphologies of both surface and sub-surface structures.…”

“…This work uses surface-fitted polynomial coefficients as the extracted features of the surface topography pattern, and will focus on GON structures. Annealed with the same initial pattern, GON and SON structures are known to temporally transform in a similar fashion 4,17 . Namely, annealing a 2-D lattice patterned initial structure yields either spherical voids or plate-shaped voids depending on the diameter, pitch, and depth of the initial pattern.…”