Integration of $\text{Er}^{3+}$-emitters in silicon-on-insulator nanodisks metasurface

TL;DR

This study demonstrates a CMOS-compatible route to enhance Er3+ emission from the telecom-band transition near $1.54 μm$ by embedding ions in silicon-on-insulator metasurfaces composed of asymmetrical nanodisks. Through Er implantation, dielectric metasurface fabrication, annealing, and extensive RT and cryogenic spectroscopy, the authors report up to 5× photoluminescence enhancement at room temperature and notable, though modest, lifetime changes linked to local density of optical states. Room-temperature PLE reveals two crystal-field regions with inhomogeneous linewidths up to 69.5 GHz, and resonant excitation yields a maximum lifetime reduction by a factor of about 2 and a peak emission enhancement of 2.9× for the line at 1.53479 μm. The work demonstrates that CMOS-compatible metasurfaces can tailor spectral and directional emission from Er emitters in SOI, enabling scalable telecom photonics and quantum devices, while highlighting the need for higher-Q designs to reach Purcell-enhanced emission.

Abstract

Erbium ($\text{Er}^{3+}$) emitters are relevant for optical applications due to their narrow emission line directly in the telecom C-band due to the ${}^\text{4}\text{I}_{\text{13/2}}$ $\rightarrow$ ${}^\text{4}\text{I}_{\text{15/2}}$ transition at 1.54 $μ$m. Additionally they are promising candidates for future quantum technologies when embedded in thin-film silicon-on-insulator (SOI) to achieve fabrication scalability and CMOS compatibility. In this paper we integrate $\text{Er}^{3+}$ emitters in SOI metasurfaces made of closely spaced array of nanodisks, to study their spontaneous emission via room and cryogenic temperature confocal microscopy, off-resonance and in-resonance photoluminescence excitation at room temperature and time resolved spectroscopy. This work demonstrates the possibility to adopt CMOS-compatible and fabrication scalable metasurfaces for controlling and improving the collection efficiency of the spontaneous emission from the $\text{Er}^{3+}$ transition in SOI and could be adopted in similar technologically advanced materials.

Figures (5)

• Figure 1: (a) Top-view SEM image of the fabricated device showing an array of 50 $\times$ 50 $\mu$m$^2$ square metasurface elements. The inset provides a zoomed-in view of one of the square metasurface elements, revealing its detailed structure. (b) Higher magnification SEM view of (a), highlighting the symmetry-breaking nanodisk array forming the metasurface. The inset further illustrates the shape and dimensions of the individual symmetry-breaking nanodisks. (c) Cross-sectional FIB image of the fabricated nanodisk array, captured at a 52$^\circ$ tilt to reveal the height and structural arrangement of the asymmetric nanodisks.
• Figure 2: $\text{Er}^{3+}$ ion implantation and photoluminescence properties: (a) Er (green) and O (blue) implantation profile in a 1:10 ratio, focusing on defect generation within the Si-layer. (b) Energy level diagram illustrating all excited transitions larin2021luminescent. (c) Obtained confocal-microscope scan illustrating the fabricated nanodisks array with 1 mW excitation at 780 nm in combination with a 900 nm longpass filter (LP). (d) Off-resonance PL-spectrum obtained for defects within the metasurface or within unfabricated (unfabr.) sections using a high NA 100X-objective, and 2mW - 976 nm excitation considering a 500 ° C anneal in (i) and 700 ° C anneal in (ii). (e) Off-resonance PL-spectrum obtained using a lower NA objective for defects within the metasurface or within unfabricated sections at 5K and RT, respectively with 2mW - 976 nm excitation. (f) $\text{Er}^{3+}$ transition line traces observed over different measurement temperatures. Data points are determined by integrating the individually obtained $\text{Er}^{3+}$ transition line spectra at 1535 nm over 3 nm around the central peak. The illustrated error-bars were defined as the square-root of the determined integral.
• Figure 3: Optical lifetime properties of observed the $\text{Er}^{3+}$-transition: (a) observed transients from the Er-O defect at 100 K; (b) Observed optical lifetimes over various measurement temperatures with 976 nm excitation-wavelength in combination with a 1550 $\pm$ 50 nm Bandpass (BP).
• Figure 4: Polarization properties of observed $\text{Er}^{3+}$-defects: (a) observed photon absorption dipole. (b) observed photon emission properties from the ensemble-defect.
• Figure 5: PLE investigation at room temperature: (a) obtained photoluminescence excitation spectrum from the Er-O implanted SOI-samples in both investigated areas (nanodisks and unfabricated). The inset illustrates the utilized experimental setup schematically; (b) exhibited inhomogeneous linewidths for all detected significant Er-O defect resonances in relation to observed wavelength where dots represent the linewidth with subsequent fitment-uncertainties illustrated as vertical error-bars. The narrowest identified resonances are shown within the inset for both, the nanodisks and the unfabricated area where a single Gaussian fit (solid lines) is applied onto the measured data (dotted); (c) lifetime-decay overview illustrated with dots in relation to observed resonance-wavelength. Subsequent fitment-uncertainties are illustrated as vertical error-bars. Normalized measured decay-transients obtained over 15 ms (dotted) with subsequently applied bi-exponential fit (solid lines) are shown within the inset from the 1534.84 nm-resonance.