Raman microscopy and infrared optical properties of SiGe Mie resonators formed on SiO₂ via Ge condensation and solid state dewetting

Abstract

All-dielectric photonics is a rapidly developing field of optics and material science. The main interest at visible and near-infrared frequencies is light management using high-refractive-index Mie-resonant dielectric particles. Most work in this area of research focuses on exploiting Sibased particles. Here, we study monocrystalline Mie-resonant particles made of Ge-rich SiGe alloys with refractive index higher than that of Si. These islands are formed via solid state dewetting of SiGe flat layers by using two different processes: (i) dewetting of monocrystalline SiGe layers (60%-80% Ge content) obtained via Ge condensation of SiGe on silicon on insulator; and (ii) dewetting of a SiGe layer deposited via molecular beam epitaxy on silicon on insulator and ex situ Ge condensation, forming a Ge-rich shell surrounding a SiGe-core. Using high-spatial-resolution Raman microscopy we monitor Ge content x and strain ò of flat layers and SiGe-islands. We observe strain relaxation associated with formation of trading dislocations in the SiGe islands compared to the starting SiGe layers, as confirmed by TEM images. For initial high Ge concentration in the flat layers, the corresponding Ge content in the dewetted islands is lower, owing to diffusion of Si atoms from Si or SiO 2 into SiGe islands. The Ge content also varies from particle to particle on the same sample. Size and shape of the dewetted particles depend on the fabrication process: thicker initial SiGe layers lead to larger particles. Samples with narrow island size distribution display rather sharp Mie resonances in the 1000-2500 nm spectral range. Larger islands display Mie resonances at longer wavelength.Positions of the resonances are in agreement with the theoretical calculations in the discrete dipole approximation.

Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe–TiO2 Films and Multilayers

“…Also, by RTA, the Si–Ge band is changed in a sharp peak at 403 cm –1 and shoulder at lower wavenumbers. These Ge–Ge and Si–Ge peaks are typical for Si 1– x Ge x NCs with excess of Ge. , If we evaluate the Ge content of Si 1– x Ge x NCs from the ratio R of the area of the Si–Ge peak ( I SiGe ) to that of the Ge–Ge peak ( I GeGe ) using the empirical formula R = I SiGe / I GeGe = 2­(1 – x )/ Bx in which B = 1.5, we obtain x = 87%. A more precise evaluation consists in computing the positions of Ge–Ge and Si–Ge peaks using the formulas ω GeGe = 280.3 + 19.4 x – 450ε and ω SiGe = 400.1 + 24.5 x – 4.5 x 2 – 33.5 x 3 – 570ε, where ε represents the strain .…”

Solid-State Dewetting Dynamics of Amorphous Ge Thin Films on Silicon Dioxide Substrates

“…Panel (c) and (d) of Figure 6 show, respectively, the corresponding peak position and FWHM, which are nearly constant through the investigated region. The extremely small fluctuations in the peak position can be interpreted easily in terms of different strain from different islands [20,21].…”

Broadband Antireflection Coatings Made of Resonant Submicron- and Micron-Sized SiGe Particles Grown on Si Substrates

“…Crystalline and polycrystalline layers are thermally more stable than amorphous ones. The particles formation on SiO2 requires temperatures ≥ 800 °C for the crystalline Si [20], [44], [45], SiGe [55]- [57] and Ge [31], [48] layers, and ≥ 700 °C for the amorphous Ge layers, depending on the thickness [32]. In the similar temperature range (≥ 750 °C), the SiGe particle formation occurs during the Ge deposition on the bare Si(100) [34], [37] and Si(111) [33], [35] substrates.…”