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Register a new userInfrared spectroscopy of silicon for applications in astronomy
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This work focuses on the characterization of various bulk silicon (Si) samples using Fourier Transform InfraRed (FTIR) and grating spectrometers in order to get them suitable for applications in astronomy. Different samples at different impurity concentrations were characterized by measuring their transmittance in the infrared region. Various lines due to residual impurity absorption were identifed and temperature dependence of impurity absorption is presented. Concentrations of doped samples (rho ~ 0.2 - 25000 Ohm cm) were determined from impurity absorption at low temperatures and from Drude free carrier absorption at 300K.
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One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III-V compound semiconductor material. In the paper we present the synthesis of single crystalline InP nanodots (NDs) on silicon using combined ion implantation and millisecond flash lamp annealing techniques. The optical and microstructural investigations reveal the growth of high-quality (100)-oriented InP nanocrystals. The current-voltage measurements confirm the formation of an n-p heterojunction between the InP NDs and silicon. The main advantage of our method is its integration with large-scale silicon technology, which allows applying it for Si-based optoelectronic devices.
In recent years, we have seen a rapid progress in the field of graphene plasmonics, motivated by graphenes unique electrical and optical properties, tunabilty, long-lived collective excitation and their extreme light confinement. Here, we review the basic properties of graphene plasmons; their energy dispersion, localization and propagation, plasmon-phonon hybridization, lifetimes and damping pathways. The application space of graphene plasmonics lies in the technologically significant, but relatively unexploited terahertz to mid-infrared regime. We discuss emerging and potential applications, such as modulators, notch filters, polarizers, mid-infrared photodetectors, mid-infrared vibrational spectroscopy, among many others.
A true monolithic infrared photonics platform is within the reach if strain and bandgap energy can be independently engineered in SiGeSn semiconductors. However, this Si-compatible family of group-IV semiconductors is typically strained and inherently metastable, making the epitaxial growth fraught with extended defects and compositional gradients. Herein, we controlled the growth kinetics to achieve epitaxial Si0.06Ge0.90Sn0.04 layers lattice-matched to a Ge on Si substrate, with a uniform content and a thickness up to 1.5 {mu}m. Atomic-level studies demonstrated high crystalline quality and uniform composition and confirmed the absence of short-range ordering and clusters. Moreover, these layers exhibit n-type conductivity that is in striking difference to the commonly observed p-type behavior in GeSn and SiGeSn alloys. Room temperature spectroscopic ellipsometry and transmission measurements showed the enhanced direct bandgap absorption at 0.83 eV and a reduced indirect bandgap absorption at lower energies. Si0.06Ge0.90Sn0.04 photoconductive devices exhibit a dark current similar to that of Ge devices and a slightly higher room-temperature spectral responsivity reaching 1 A/W above 0.82 eV (i.e. below 1.5 {mu}m wavelengths). These results underline the enhanced performance in lattice-matched devices and pave the way to introduce SiGeSn semiconductors as building blocks to implement the long-sought-after silicon-integrated infrared optoelectronics.
Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um.
Photoluminescence (PL) spectra of single silicon vacancy (SiV) centers frequently feature very narrow room temperature PL lines in the near-infrared (NIR) spectral region, mostly between 820 nm and 840 nm, in addition to the well known zero-phonon-line (ZPL) at approx. 738 nm [E. Neu et al., Phys. Rev. B 84, 205211 (2011)]. We here exemplarily prove for a single SiV center that this NIR PL is due to an additional purely electronic transition (ZPL). For the NIR line at 822.7 nm, we find a room temperature linewidth of 1.4 nm (2.6 meV). The line saturates at similar excitation power as the ZPL. ZPL and NIR line exhibit identical polarization properties. Cross-correlation measurements between the ZPL and the NIR line reveal anti-correlated emission and prove that the lines originate from a single SiV center, furthermore indicating a fast switching between the transitions (0.7 ns). g(2) auto-correlation measurements exclude that the NIR line is a vibronic sideband or that it arises due to a transition from/to a meta-stable (shelving) state.
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