Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks

GeSn alloys with Sn contents of 8.4 % and 10.7 % are grown pseudomorphically on Ge buffers on Si (001) substrates. The alloys as-grown are compressively strained, and therefore indirect bandgap. Undercut GeSn on Ge microdisk structures are fabricated and strained by silicon nitride stressor layers, which leads to tensile strain in the alloys, and direct bandgap photoluminescence in the 3–5 µm gas sensing window of the electromagnetic spectrum. The use of pseudomorphic layers and external stress mitigates the need for plastic deformation to obtain direct bandgap alloys. It is demonstrated, that the optically pumped light emission overlaps with the methane absorption lines, suggesting that GeSn alloys are well suited for mid-infrared integrated gas sensors on Si chips

Mid-Infrared Intersubband Absorption from P-Ge Quantum Wells on Si

Mid-infrared intersubband absorption from p-Ge quantum wells with Si0.5Ge0.5 barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness. Fourier transform infra-red spectroscopy measurements demonstrate clear absorption peaks corresponding to intersubband transitions among confined hole states. The work indicates an approach that will allow quantum well intersubband photodetectors to be realized on Si substrates in the important atmospheric transmission window of 8–13 μm

Mid-infrared intersubband absorption from p-Ge quantum wells grown on Si substrates

Mid-infrared intersubband absorption from p-Ge quantum wells with Si0.5Ge0.5 barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness. Fourier transform infra-red transmission and photoluminescence measurements demonstrate clear absorption peaks corresponding to intersubband transitions among confined hole states. The work indicates an approach that will allow quantum well intersubband photodetectors to be realized on Si substrates in the important atmospheric transmission window of 8–13 μm

Tensile Strained GeSn Mid-Infrared Light Emitters

Compressively strained GeSn alloys grown on Ge buffers on Si (001) substrates were fabricated into microdisks and strained using silicon nitride stressors. The strained disks are measured to be tensile by Raman spectroscopy, and demonstrate direct bandgap emission in the 3-5 μm gas sensing window

Towards a Mid-Infrared Lab-on-Chip Sensor using Ge-on-Si Waveguides

For the last decade, germanium has been proposed as an excellent material for passive mid-infrared (MIR) integrated photonics. This technology allows for label-free sensing in the molecular fingerprint regime (6.7–20 μm), where molecules can be uniquely identified by their absorption spectra. Such a platform has the potential to enable low cost, miniaturized mid-infrared sensors for use in crucial applications such as explosives detection, pollution monitoring and detection of breath biomarkers for point of care diagnostics. There have now been a number of demonstrations of waveguides up to 8.5 μm wavelength using Ge [1] and SiGe [2] waveguides. Previously, we have demonstrated the first low loss Ge-on-Si waveguides from 7.5 to 11 μm, with losses as low as ∼1 dB/cm [3]. Here, we demonstrate their potential for sensing applications by evanescently sensing unique vibrations in poly(methyl methacrylate) (PMMA) polymers, in the spectral region of 7.5–10 μm wavelength

Molecular Fingerprint Sensing Using Ge-on-Si Waveguides

Germanium-on-silicon, mid-infrared waveguides are used to demonstrate molecular fingerprint sensing of poly(methyl methacrylate) between 7.5 and 10 μm wavelength. The results are compared to Fourier transform infrared spectroscopy measurements, highlighting the potential of the platform for the identification of analytes

Primary accumulation in the Soviet transition

The Soviet background to the idea of primary socialist accumulation is presented. The mobilisation of labour power and of products into public sector investment from outside are shown to have been the two original forms of the concept. In Soviet primary accumulation the mobilisation of labour power was apparently more decisive than the mobilisation of products. The primary accumulation process had both intended and unintended results. Intended results included bringing most of the economy into the public sector, and industrialisation of the economy as a whole. Unintended results included substantial economic losses, and the proliferation of coercive institutions damaging to attainment of the ultimate goal - the building of a communist society

Expanding the Ge emission wavelength to 2.25 μm with SixNy strain engineering

Photoluminescence up to 2.25 μm wavelength is demonstrated from Ge nanopillars strained by silicon nitride stressor layers. Tensile biaxial equivalent strains of up to ~1.35% and ~0.9% are shown from 200 × 200 nm, and 300 × 300 nm square top Ge pillars respectively. Strain in the latter is confirmed by Raman spectroscopy, and supported by finite element modelling, which gives an insight into the strain distribution and its effect on the band structure, in pillar structures fully coated by silicon nitride stressor layers

Extending the emission wavelength of Ge nanopillars to 2.25 μm using silicon nitride stressors

The room temperature photoluminescence from Ge nanopillars has been extended from 1.6 μm to above 2.25 μm wavelength through the application of tensile stress from silicon nitride stressors deposited by inductively-coupled-plasma plasma-enhanced chemical-vapour-deposition. Photoluminescence measurements demonstrate biaxial equivalent tensile strains of up to ~ 1.35% in square topped nanopillars with side lengths of 200 nm. Biaxial equivalent strains of 0.9% are observed in 300 nm square top pillars, confirmed by confocal Raman spectroscopy. Finite element modelling demonstrates that an all-around stressor layer is preferable to a top only stressor, as it increases the hydrostatic component of the strain, leading to an increased shift in the band-edge and improved uniformity over top-surface only stressors layers

High-Q Si3N4 Ring Resonators for Locking 780nm GaAs-Based Distributed Feedback Laser

High-Q microring resonators have applications in gyroscopes, frequency comb generation, and feedback systems to control narrow linewidth integrated lasers [1–3]. This paper demonstrates the highest Q values measured for microring resonators at 780 nm wavelength. These sub mm integrated cavities can be used to provide an error signal for locking a distributed feedback laser (DFB), Fig. 1(a), using the Pound-Drever-Hall (PDH) method. High stability DFBs can also be achieved using a micro-electro-mechanical system (MEMS) cell containing 87 Rb vapour and taking advantage of the absorption line at 780.24 nm. This provides an absolute reference for locking the laser but only to the 87 Rb transition wavelengths. The microring resonator can be tailor made for any wavelength but is susceptible to thermal effects; this could in part be overcome using a top cladding with a thermo-optic coefficient that counteracts that of the waveguide core