Anomalous form-birefringence induced in an amorphous Si thin layer by ultraviolet laser scanning

초록

A 355 nm nanosecond laser was employed to crystallize a 45-nm-thick amorphous silicon (a-Si) film on a glass substrate, generating surface ripples with a periodicity of 330 nm perpendicular to the laser polarization. The transmittance spectra exhibited three resonance dips at 405 nm (M1), 507 nm (M2), and 691 nm (M3), with intensities varying according to the polarization state. The M2 mode displayed a resonance dip under transverse magnetic (TM) polarization, while the M1 and M3 modes exhibited resonance dips under transverse electric (TE) polarization. Modeling the periodic surface ripples as 1D gratings, rigorous coupled-wave analysis (RCWA) revealed that each resonance corresponded to a guided-mode resonance (GMR) localized within the Si layer beneath the grating. Furthermore, the GMR led to strongly wavelength-dependent birefringence, reaching values several hundreds of times greater than in intrinsic bulk Si due to resonance-enhanced field confinement. Additionally, the transmittance of the sample under a near-crossed polarizer configuration could be tuned by adjusting the relative angle between the polarizers. These findings highlight the potential for wavelengthselective birefringence tuning, which may be beneficial for applications in optical sensing and polarizationcontrol devices.

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