Towards monolithic integration of germanium light sources on silicon chips

Germanium (Ge) is a group-IV indirect band gap semiconductor, and therefore bulk Ge cannot emit light efficiently. However, the direct band gap energy is close to the indirect one, and significant engineering efforts are being made to convert Ge into an efficient gain material monolithically integrated on a Si chip. In this article, we will review the engineering challenges of developing Ge light sources fabricated using nano-fabrication technologies compatible with Complementary Metal-Oxide-Semiconductor (CMOS) processes. In particular, we review recent progress in applying high-tensile strain to Ge to reduce the direct band gap. Another important technique is doping Ge with donor impurities to fill the indirect band gap valleys in the conduction band. Realization of carrier confinement structures and suitable optical cavities will be discussed. Finally, we will discuss possible applications of Ge light sources in potential photonics-electronics convergent systems

Photonic crystal waveguides on silicon rich nitride platform

We demonstrate design, fabrication, and characterization of two-dimensional photonic crystal (PhC) waveguides on a suspended silicon rich nitride (SRN) platform for applications at telecom wavelengths. Simulation results suggest that a 210 nm photonic band gap can be achieved in such PhC structures. We also developed a fabrication process to realize suspended PhC waveguides with a transmission bandwidth of 20 nm for a W1 PhC waveguide and over 70 nm for a W0.7 PhC waveguide. Using the Fabry–Pérot oscillations of the transmission spectrum we estimated a group index of over 110 for W1 PhC waveguides. For a W1 waveguide we estimated a propagation loss of 53 dB/cm for a group index of 37 and for a W0.7 waveguide the lowest propagation was 4.6 dB/cm

Tensile strain engineering of germanium micro-disks on free-standing SiO2 beams

Tensile strain is required to enhance light-emitting direct-gap recombinations in germanium (Ge), which is a promising group IV material for realizing a monolithic light source on Si. Ge micro-disks on free-standing SiO2 beams were fabricated using Ge-on-Insulator wafers for applying tensile strain to Ge in a structure compatible with an optical confinement. We have studied the nature of the strain by Raman spectroscopy in comparison with finite-element computer simulations. We show the impacts of the beam design on the corresponding strain value, orientation, and uniformity, which can be exploited for Ge light emission applications. It was found that the tensile strain values are larger if the length of the beam is smaller. We confirmed that both uniaxial and biaxial strain can be applied to Ge disks, and maximum strain values of 1.1 and 0.6% have been achieved, as confirmed by Raman spectroscopy. From the photoluminescence spectra of Ge micro-disks, we have also found a larger energy splitting between the light-hole and the heavy-hole bands in shorter beams, indicating the impact of tensile strain

Enhanced light emission from improved homogeneity in biaxially suspended Germanium membranes from curvature optimization

A silicon compatible light source is crucial to develop a fully monolithic silicon photonics platform. Strain engineering in suspended Germanium membranes has offered a potential route for such a light source. However, biaxial structures have suffered from poor optical properties due to unfavorable strain distributions. Using a novel geometric approach and finite element modelling (FEM) structures with improved strain homogeneity were designed and fabricated. Micro-Raman (μ-Raman) spectroscopy was used to determine central strain values. Micro-photoluminescence (μ-PL) was used to study the effects of the strain profiles on light emission; we report a PL enhancement of up to 3x by optimizing curvature at a strain value of 0.5% biaxial strain. This geometric approach offers opportunity for enhancing the light emission in Germanium towards developing a practical on chip light source

Tensile strain of germanium micro-disks on freestanding SiO2 beams

Tensile strain is crucial to expect the direct recombination in germanium (Ge), towards monolithic light sources on silicon (Si). Freestanding beams of Ge are known to produce strong tensile strain, however, it is not trivial to construct a cavity in a freestanding structure. Here, we fabricated Ge micro-disks on freestanding oxide beams, and observed Whispering-Gallery-Modes (WGM) by photoluminescence. The tensile strain was larger in shorter beams, which is consistent with simulations

Spatially resolved spectroscopy for monitoring the solvent content in pharmaceutical drying

The pharmaceutical drying process is critical to the quality of the active pharmaceutical ingredient or the drug product as it is often the final unit operation. The non-uniformity of drying is particularly challenging as it renders inaccurate the determined solvent content and drying endpoint, which is a critical quality attribute. As process analytical technology further develops, novel techniques are implemented to address process and product challenges. Spatially resolved spectroscopy is a technique in which spectra are collected from spatially resolved distances from the incident light. This technique is used for the characterisation of non-uniform media. In this thesis, the use of spatially resolved spectroscopy for the monitoring of the drying of an active pharmaceutical ingredient is reported. Pharmaceutical drying of model systems was monitored using spatially resolved spectroscopy. In this work, three bespoke probes were used for the collection of spatially resolved spectra. One probe allows the collection of spatially and angularly resolved diffuse reflectance near-infrared measurements (SAR-DRM), while the other was developed for the collection of spatially offset Raman spectroscopy (SORS) measurements. The third probe combines both techniques and was developed for the collection of both spatially resolved near-infrared spectra and spatially offset Raman spectra and is termed the combined probe. This thesis details the in-line and at-line application for industrial process monitoring using these techniques, which to our knowledge were not applied in this setting. The drying of two grades of paracetamol, granular and powder, in the solvents n-heptane and methyl tert-butyl ether was monitored using SAR-DRM. The drying of granular and powder paracetamol in the solvents anisole and methyl tert-butyl ether was monitored using SORS. Partial least squares regression (PLSR) analysis was used for the estimation of the solvent content using spectra from the individual signal collection configurations, in addition to a combination of the configurations. Results from both techniques suggest that PLSR models of spectra collected from larger distances lead to more accurate vii estimations of the solvent content. This was attributed to the larger volume of the drying powder cake probed by those techniques. Since the drying of paracetamol in methyl tert-butyl ether could be monitored using both techniques, the combined probe was used for monitoring this system, and multi-block PLSR analysis was conducted using both near-infrared and Raman spectra of combinations of the configurations. The multi-block PLSR model performance was similar to that of the individual SORS spectra, which was attributed to the stronger signals and spectral features of the Raman signal compared to the near-infrared measurements. Since the application of SORS for the monitoring of pharmaceutical drying was demonstrated and showed improvement in PLSR model performance and solvent content estimation, SORS was further used for the monitoring of the washing with methyl tert-butyl ether a paracetamol filter cake wet with anisole. The results similarly showed improved estimations of the content of both solvents in the filter cake from spectra from larger offset distances. The outcomes of the studies in this thesis demonstrate the advantage of the application of spatially resolved spectroscopy for monitoring the solvent content in pharmaceutical drying. The use of such novel process analytical technology offers potential for improved process monitoring and accurate prediction of the process end point.The pharmaceutical drying process is critical to the quality of the active pharmaceutical ingredient or the drug product as it is often the final unit operation. The non-uniformity of drying is particularly challenging as it renders inaccurate the determined solvent content and drying endpoint, which is a critical quality attribute. As process analytical technology further develops, novel techniques are implemented to address process and product challenges. Spatially resolved spectroscopy is a technique in which spectra are collected from spatially resolved distances from the incident light. This technique is used for the characterisation of non-uniform media. In this thesis, the use of spatially resolved spectroscopy for the monitoring of the drying of an active pharmaceutical ingredient is reported. Pharmaceutical drying of model systems was monitored using spatially resolved spectroscopy. In this work, three bespoke probes were used for the collection of spatially resolved spectra. One probe allows the collection of spatially and angularly resolved diffuse reflectance near-infrared measurements (SAR-DRM), while the other was developed for the collection of spatially offset Raman spectroscopy (SORS) measurements. The third probe combines both techniques and was developed for the collection of both spatially resolved near-infrared spectra and spatially offset Raman spectra and is termed the combined probe. This thesis details the in-line and at-line application for industrial process monitoring using these techniques, which to our knowledge were not applied in this setting. The drying of two grades of paracetamol, granular and powder, in the solvents n-heptane and methyl tert-butyl ether was monitored using SAR-DRM. The drying of granular and powder paracetamol in the solvents anisole and methyl tert-butyl ether was monitored using SORS. Partial least squares regression (PLSR) analysis was used for the estimation of the solvent content using spectra from the individual signal collection configurations, in addition to a combination of the configurations. Results from both techniques suggest that PLSR models of spectra collected from larger distances lead to more accurate vii estimations of the solvent content. This was attributed to the larger volume of the drying powder cake probed by those techniques. Since the drying of paracetamol in methyl tert-butyl ether could be monitored using both techniques, the combined probe was used for monitoring this system, and multi-block PLSR analysis was conducted using both near-infrared and Raman spectra of combinations of the configurations. The multi-block PLSR model performance was similar to that of the individual SORS spectra, which was attributed to the stronger signals and spectral features of the Raman signal compared to the near-infrared measurements. Since the application of SORS for the monitoring of pharmaceutical drying was demonstrated and showed improvement in PLSR model performance and solvent content estimation, SORS was further used for the monitoring of the washing with methyl tert-butyl ether a paracetamol filter cake wet with anisole. The results similarly showed improved estimations of the content of both solvents in the filter cake from spectra from larger offset distances. The outcomes of the studies in this thesis demonstrate the advantage of the application of spatially resolved spectroscopy for monitoring the solvent content in pharmaceutical drying. The use of such novel process analytical technology offers potential for improved process monitoring and accurate prediction of the process end point

Analysis of Vision based Techniques for the Translation of Indian Sign Language

Sign language acts as a medium of communication among those of the hearing impaired and mute community. However, it cannot be easily understood by common people. Various research has been done to bridge this gap by developing Sign Language Recognition (SLR) methodologies. Studies say that 1 in every 5 deaf people is Indian. In this paper, a thorough review of these methodologies has been done, to compare and contrast various aspects of them. This includes an overview on different preprocessing methods used like segmentation, image morphological processing, cropping, etc, feature extraction techniques like Fourier Descriptors, Image Moments, Eigen values, Mediapipe and others. This study also covered classification models spanning from Distance metrics to Kernel based approaches and feedforward neural networks, along with Deep Learning based methods such as CNNs, LSTMs, GANs, Transformers etc

Strain-engineering in Germanium membranes towards light sources on Silicon

Bi-axially strained Germanium (Ge) is an ideal material for Silicon (Si) compatible light sources, offering exciting applications in optical interconnect technology. By employing a novel suspended architecture with an optimum design on the curvature, we applied a biaxial tensile strain as large as 0.85% to the central region of the membrane