Abstract

We report the design and fabrication of single-material distributed Bragg reflectors (DBRs) composed of amorphous germanium (a-Ge) thin films by a glancing angle deposition and their optical reflectance characteristics in the long wavelength region of 1.7–3.1 μm, together with the aid of theoretical analysis using a rigorous coupled-wave analysis method. The refractive index of the a-Ge films is estimated from the measured transmittance spectra. The high and low refractive indices a-Ge films (i.e., $\mathrm{\Delta }n\sim 2.18$), which compose the alternative layers of DBRs, were fabricated at two incident vapor flux angles (${\theta }_{\alpha }$) of 0° and 80°, respectively, by determining the quarter wavelength thicknesses of 135 nm at ${\theta }_{\alpha }=0°$ and 291 nm at ${\theta }_{\alpha }=80°$ for a center wavelength (${\lambda }_c$) of $\sim 2.2\mathrm{\mu m}$. For the fabricated a-Ge/a-Ge DBR with only 5 pairs, the normalized stop bandwidth ($\mathrm{\Delta }\lambda /{\lambda }_c$) of $\sim 22.3\%$ was measured while maintaining high reflectance values of $>99\%$ over a wide wavelength range of 2.06–2.55 μm, which indicates a reasonable consistency with the calculated reflectance results.

© 2013 Optical Society of America

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