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Molecular beam epitaxy (MBE) was used to grow dissimilar materials like cubic Ge on a hexagonal c-plane sapphire substrate. To the authors' best knowledge, this is the first time single crystalline Ge was grown on a c-plane sapphire substrate.

Group-IV alloy GeSn holds great promise for the high-performance optoelectronic devices that can be monolithically integrated on Si for near- and mid-infrared applications. Growth of GeSn using chemical vapor deposition technique with various Sn and Ge precursors has been investigated worldwide. To achieve relatively high Sn incorporation, the use of higher pressure and/or higher order Ge hydrides precursors were reported. In this work, we successfully demonstrated the growth of high-quality GeSn with Sn composition of 16.7% at low pressure of 12 Torr. The alloy was grown using the commercially available GeH4 and SnCl4 precursors via a chemical vapor deposition reactor. Material and optical characterizations were performed to confirm the Sn incorporation and to study the optical properties. The demonstrated growth results reveal a low-pressure growth window to achieve high-quality and high Sn alloys for future device applications.

The value added along the tilapia value chain is hardly defined in Ghana, and as such, the benefits associated with the various costs along the chain are not fully documented and realized. The study sought to assess and analyze the tilapia value chain by assessing the profile of the actors, existing linkages and value added at each stage of the chain. Also, the profitability of chain activities pertaining to tilapia as well as constraints faced by the actors in the pursuit of their business were determined. The study was carried out in the Eastern and Greater Accra regions of Ghana and primary data was collected from 100 respondents, made up of 40 tilapia producers (farmers), 30 tilapia processors and 30 tilapia distributors. Returns on Investment (ROI), Net Farm Incomes (NFI) and profit margins were estimated and used to measure the distribution of benefit along the chain. Actors along the tilapia value chain were found to add a substantial amount of value, with producers contributing the highest (GHS 2449.65). Also, returns were found to be unequally distributed along the chain with producers having the greatest margin of 5.17/kg. The determinants of profitability for actors include pond size, belonging to an association, time of harvesting, extension officer visits, farm ownership, gender, experience, availability of a ready supplier, ability to buy tilapia on credit, household size, experience and premium.

Recent studies of SiGeSn materials and optoelectronic devices hold great promise for photonics integrated circuits (PICs) on Si platform featuring scalable, cost-effective, and power-efficient. Thanks to the breakthrough of low temperature material growth techniques, device-quality level materials have been grown, following by the demonstration of light-emitting diodes, photodetectors, and optically pumped and electrically injected band-to-band lasers. While the exciting developments in bulk devices were reported, the quantum wells (QWs) have been investigated targeting the dramatically improved and/or novel device performance via variety of quantum confinement effects. In this review, we summarize the recent progress on development of SiGeSn QWs, including the fundamental optical and transition studies and optoelectronic device applications. The inspirational results reveal the possibility of all-group-IV PICs with photonics and electronics monolithically integrated on a single-chip.

In this work, a SiGeSn/GeSn/SiGeSn single quantum well was grown and characterized. The sample has a thicker GeSn well of 22nm compared to a previously reported 9nm well configuration. The thicker well leads to: (i) lowered ground energy level in Γ valley offering more bandgap directness; (ii) increased carrier density in the well; and (iii) improved carrier collection due to increased barrier height. As a result, significantly enhanced emission from the quantum well was observed. The strong photoluminescence (PL) signal allows for the estimation of quantum efficiency (QE), which was unattainable in previous studies. Using pumping-power-dependent PL spectra at 20K, the peak spontaneous QE and external QE were measured as 37.9% and 1.45%, respectively.

We demonstrated electrically injected GeSn laser with the threshold to as low as 353 A/cm2 at 10 K. The threshold reduction was achieved by introducing a thicker SiGeSn cap, eliminating the optical loss from the top metal contact. The peak power was measured as 2.75 mW/facet at 10 K. At 110 K, the emission peak is at 2604 nm.

GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-IV direct-bandgap material. The GeSn laser study recently moved from optical pumping into electrical injection. In this work, we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions. Cap layer material was studied by using Si 0.03 Ge 0.89 Sn 0.08 and Ge 0.95 Sn 0.05 , and cap layer total thickness was also compared. The 190 nm SiGeSn-cap device had threshold of 0.6 kA / cm 2 at 10 K and a maximum operating temperature ( T max ) of 100 K, compared to 1.4 kA / cm 2 and 50 K from 150 nm SiGeSn-cap device, respectively. Furthermore, the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA / cm 2 and T max at 90 K, i.e., higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer, indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably. The study of the active region material showed that device gain region using Ge 0.87 Sn 0.13 had a higher threshold and lower T max , compared to Ge 0.89 Sn 0.11 . The performance was affected by the metal absorption, free carrier absorption, and possibly defect density level. The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge 0.87 Sn 0.13 in gain regions. The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-IV photonics on a Si platform.

Silicon-tin (Si1-xSnx) films have been grown using plasma-enhanced chemical vapor deposition on Si (001) substrate. X-ray photoelectron spectroscopy characterization of the thin films show successful substitutional incorporation of Sn in Si lattice up to 3.2%. The X-ray diffraction characterizations show epitaxial growth of Si1-xSnx films (001) direction. The Sn incorporation has been measured using X-ray photoelectron spectrometry and the film uniformity was confirmed using energy dispersive X-ray spectrometry.

Monolithic lasers on Si have long been anticipated as an enabler of full photonic integration, and significant progress in GeSn material development shows promise for such laser devices. While there are many reports focused on optically pumped lasers, in this work, we demonstrate electrically injected GeSn lasers on Si. We grew a GeSn/SiGeSn heterostructure diode on a Si substrate in a ridge waveguide laser device and tested it under pulsed conditions, giving consideration to the structure design to enhance the carrier and optical confinement. The peak linewidth of 0.13 nm (0.06 meV) and injection current curves indicated lasing, which was observed up to 100 K with emission peaks at 2300 nm. We recorded a threshold of 598 A / c m 2 at 10 K. The peak power and external quantum efficiency were 2.7 mW/facet and 0.3%, respectively. The results indicate advances for group-IV-based lasers, which could serve as a promising route for laser integration on Si.