Dependence of light reflection of germanium Mie nanoresonators on their aspect ratio

The light reflection spectra of Ge disk nanoresonators on a Si substrate are studied, depending on their diameter (d) and height (h). The Ge disks, fabricated at temperatures close to room temperature using the bottom-up approach, exhibit a polycrystalline structure. The reflection at resonance wavelengths decreases more than 10 times, compared to surface areas without disks when the disk aspect ratio h/d increases to 1.0 and d > 100 nm. The strong dependence of the reflection minimum on h/d can be associated with the influence of the substrate. An effective refractive index, defined as neff = lambda(m)/d and determining the long-wavelength resonance mode position lambda(m), turns out to be larger for disks than for spheres. It is also significantly larger than the Ge refractive index. This allows the use of disks of smaller diameter than spheres to achieve the resonance effects at the same wavelength.