Low temperature deactivation of Ge heavily n-type doped by ion implantation and laser thermal annealing

International audienceHeavy doping of Ge is crucial for several advanced micro-and optoelectronic applications, but, at the same time, it still remains extremely challenging. Ge heavily n-type doped at a concentration of 1 X 10(20) cm(-3) by As ion implantation and melting laser thermal annealing (LTA) is shown here to be highly metastable. Upon post-LTA conventional thermal annealing As electrically deactivates already at 350 degrees C reaching an active concentration of similar to 4 x 10(19) cm(-3). No significant As diffusion is detected up to 450 degrees C, where the As activation decreases further to similar to 3 x 10(19) cm(-3). The reason for the observed detrimental deactivation was investigated by Atom Probe Tomography and in situ High Resolution X-Ray Diffraction measurements. In general, the thermal stability of heavily doped Ge layers needs to be carefully evaluated because, as shown here, deactivation might occur at very low temperatures, close to those required for low resistivity Ohmic contacting of n-type Ge

Plasmonic response of chalcogenides and switchable all-dielectric metamaterials

Crystalline germanium antimony telluride shows a profound plasmonic response in the optical-UV spectral range that disappears in the chalcogenides’s amorphous state. We harness this effect to realize tuneable and plasmonic/all-dielectric phase-change memory metasurfaces

Fibre-coupled photonic metadevices

We report on metadevices realised by integration of functional metamaterials with single-mode telecoms fibres. These include plasmonic and all-dielectric nonlinear, nano-opto-mechanical and phase-change switching, dispersion manipulation and coherent absorber metadevices

Chalcogenide platforms for photonic metamaterials

Photonic metamaterials - media artificially structured at the nanometre scale - provide extraordinary optical properties not found in nature. In this work I explored opportunities provided by changes of complex optical properties of chalcogenide alloys related to compositional variation and structural phase change to develop switchable and tunable plasmonic and dielectric metamaterials:• I have systematically explored the properties of Bi:Sb:Te across UV to near infrared wavelengths through combinatorial high-throughput mapping techniques for the widest compositional spread reported so far. This study reveals that Bi:Sb:Te has better plasmonic properties than gold at wavelengths below 580 nm and silver below 365 nm; ability to support dielectric (Mie) resonances better than oxides at telecommunication wavelengths beyond 1200 nm; epsilon-near-zero properties across UV to IR wavelengths; sub-unity refractive index (down to 0.7) in the UV and the highest refractive index in the near-IR (up to 11.5 at 1680 nm) reported so far to our knowledge.• I have studied for the first time the plasmonic character of amorphous Bi:Te and developed resonant optical metasurfaces based on this alloy that present strong, period-dependent plasmonic absorption resonances (QMax = 7.5) in the visible range. Furthermore, I have investigated changes of optical properties of this alloy upon structural phase change from amorphous to crystalline phases.• I have studied for the first time channelling of light through nano-hole arrays filled with dispersive low-epsilon chalcogenides. The complex changes in the composite’s spectral response depend strongly on the interplay between the dispersion of the optical properties of the plasmonic nanostructure and the low-epsilon medium and lead to increase of transmission over a broad range of plasmonic frequencies.• I have developed the first switchable UV metamaterials that exploits the low refractive index (equal to 1.07 at 245 nm for c-GST) and phase change properties of chalcogenides. In particular, I have shown that laser-induced structural phase transitions can be used to switch quality factors of dielectric resonances (QMax = 15) in metamaterials without affecting their spectral positions

Tuneable epsilon near-zero in chalcogenides

The enormous potential of chalcogenides as compositionally-tuneable alternatives to noble metals for plasmonics and ‘epsilon-near-zero’ (ENZ) photonics can be unlocked using high-throughput materials discovery techniques. Taking advantage of the composition-dependent plasmonic properties of binary and ternary telluride alloys, we show the first amorphous ENZ and plasmonic metasurfaces operating across the UV-VIS spectral range

Hollow-core waveguides with n<1 chalcogenide cladding

We utilize compositionally controlled low refractive index (n<1) chalcogenide semiconductors in hollow-core waveguides operating across ultraviolet frequencies. Such materials enable π-phase shifts over nanometric propagation lengths in slab and fibre configurations

Reconfigurable ultraviolet and high-energy-visible dielectric metamaterials

Photonic materials with tuneable and switchable ultraviolet (UV) to high-energy-visible (HEV) optical properties would benefit applications in sensing, high-density optical memory, beam-steering, adaptive optics and light modulation. Here, for the first time, we demonstrate a non-volatile switchable dielectric metamaterial operating in the UV-HEV spectral range. Nano-grating metamaterials in a layered composite of low-loss ZnS/SiO2 and the chalcogenide phase-change medium germanium antimony telluride (Ge2Sb2Te5) exhibit reflection resonances at UV-HEV wavelengths that are substantially modified by light-induced (amorphous-crystalline) phase transitions in the chalcogenide layer. Despite the presence of the lossy GST, resonance quality factors up to Q~15 are ensured by the transparency (low losses) of ZnS/SiO2 in the UV-HEV spectral range and values of Q increase as the refractive index of Ge2Sb2Te5 decreases, upon crystallization. Notably however, this switching leaves resonance spectral positions unchanged

UV resonance switching dataset

Dataset for &quot;Reconfigurable Ultraviolet and High-Energy Visible Dielectric Metamaterials&quot; published in Nano Letters.</span

Compositionally controlled plasmonics in amorphous semiconductor metasurfaces

Amorphous bismuth telluride (Bi:Te) provides a composition-dependent, CMOS-compatible alternative material platform for plasmonics in the ultraviolet-visible spectral range. Thin films of the chalcogenide semiconductor are found, using high-throughput physical vapor deposition and characterization techniques, to exhibit a plasmonic response (a negative value of the real part of relative permittivity) over a band of wavelengths extending from ~250 nm to between 530 and 978 nm, depending on alloy composition (Bi:Te at% ratio). The plasmonic response is illustrated via the fabrication of subwavelength period nano-grating metasurfaces, which present strong, period-dependent plasmonic absorption resonances in the visible range, manifested in the perceived color of the nanostructured domains in reflection