Skip to main content

Postgraduate Research on Dilute Metamorphic Nanostructures and Metamaterials in Semiconductor Photonics

Periodic Reporting for period 2 - PROMIS (Postgraduate Research on Dilute Metamorphic Nanostructures and Metamaterials in Semiconductor Photonics)

Reporting period: 2017-01-01 to 2018-12-31

Photonics, nanotechnology, advanced materials, and advanced manufacturing have been identified as key enabling technologies for the EU. The photonics global market alone is around €300 billion and Europe has established a strong position with a total share of 20%, directly employing about 290,000 people. However, the shortage of skilled labour and entrepreneurs remains a major problem. Tailoring of semiconductors at the nanoscale is an important enabling technology for a wide range of photonics and electronics applications in diverse areas. In this training network, a cohort of 16 early stage researchers were trained in the full range of skills required for a career in photonics, including materials growth, device fabrication, characterisation, design, theory, and commercialisation. A carefully-chosen consortium of 8 academic partners, 2 full industry partners and 7 associated partners provided the training in these skills, with European and worldwide reputations as leaders in each field. These skills were developed within four burgeoning research areas; Semiconductor Metamaterials & Plasmonics, Dilute Nitride semiconductor nanostructures, Hydrogenated semiconductors and Metamorphic structures. The outcomes of this enabling fundamental research delivered advances in sources for secure communications, sensitive detectors for security applications, more efficient solar cells for energy generation, LEDs and sensors for environmental gas and bio-sensing. Each researcher experienced both academic and commercial environments thanks to the strong industrial involvement, resulting in multi-skilled, industry-focused graduates.
The PROMIS network organised 4 workshops, a summer school and a conference. The workshops addressed the topics of Growth and Fabrication of Photonic Materials and Devices (Sheffield, September 2015), Design and modelling of Photonic devices (Cadiz, May 2016), Characterisation of Photonic materials and devices (Rome, June 2017) and Photonics in Industry, IP and Career development (Nottingham, April 2018). Attracting attendances of ~40 people, they included tutorial-style talks from high-profile speakers, as well as soft skills activities for the ESRs - presentation skills, outreach training and mock job interviews etc. The PROMIS Summer School was organised in collaboration with the international MBE conference, and was held over 2 weeks in Montpellier, in September, 2016. The Summer School also provided soft skills training, including creating short videos, to support our other outreach events, and a PROMIS Photonics event at Millennium Point, Birmingham in November 2017, where our ESRs showcased their research to the general public. The final conference –Photonics by the Lake- was held in July 2018 in the Lake District, UK, with over 50 attendees and featured talks from internationally leading invited speakers in Photonics as well as non-PROMIS postgraduate students. 8 of the 16 ESRs in PROMIS have successfully defended their theses, with the remaining 8 expected to complete within the next few months, and 4 are already in employment. The network has published over 40 journal articles and 2 book chapters. The project website and other social media has been popular and extensively used to promote our activities.
Work Package 1: Practical strategies were developed for the realization of novel single-photon sources based on hydrogenated (InGa)(AsN) quantum dots (QDs) for photonic devices. ROME and UMR found that the H concentration profile can be modulated with a precision of a few nm using the hot spot of a scanning near-field optical microscope. This allowed the fabrication of site-controlled, single-photon-emitting QDs, which perform as excellent single-photon sources, with highly uniform emission energy. These will be integrated into photonic crystal cavities and LEDs for enhanced telecommunications. Tyndall-UCC contributed detailed theoretical studies and delivered novel designs for optimised strain-balanced 3.3 µm and 4.2 µm LED structures on metamorphic substrates (WP4) and theoretical analysis of GaSb/GaAs QDs and quantum rings to elucidate how electronic structure evolves with dot/ring shape and consequences for solar cells (WP3).

Work Package 2: APDs with low dark current were realized at SHEFF by addition of Ga to the very thin AlGaAsSb avalanche layer which reduced the surface leakage current, (with lifetimes measured at Tyndall-UCC), without any significant band to band tunnelling. A new etchant was developed for InGaAs-AlGaAsSb APDs which produced more uniform dark current. The AlGaAsSb APDs were significantly more tolerant to temperature fluctuation than commercial APDs. Gallium nanoparticle layers were deposited on top of InGaAs APDs by UAM which improved their sensitivity. New methods for the production of colloidal Ga nanoparticles were also developed which exhibit tunability and strong plasmonic absorption in the UV, depending on the nanoparticle dimensions and aggregation state. A particular highlight was the first high speed, fully integrated Quantum Random Number generator chip demonstrated by IDQuantique and TUDelft, leading to an innovative Quanta Image Sensor with Dartmouth College, for which a patent is filed.

Work Package 3: Both tandem and intermediate band solar cells were studied. III-V Lab advanced the state of the art of InP-based solar cells grown by MOVPE using a novel tunnel junction. InP and InGaAs single junction cells grown on InP showed efficiencies of 13.5% and 11.4%, respectively, while the InP/InGaAs tandem cell exhibited a conversion efficiency of 18.3%. The same architecture was grown and validated on a commercial InP/Si template. GaSb single-junction solar cells grown by MBE on GaSb at UM exhibited state of the art performance with 5.9% efficiency. The first AlInAsSb/GaSb tandem solar cells were successfully fabricated, with efficiency limited by the top cell. ULANC (with TEM at UCA) demonstrated type II intermediate band solar cells containing 40 layers of GaSb quantum rings - the highest reported to date - without introducing additional dislocations, resulting in enhancement of sub-bandgap absorption and partial VOC recovery under concentration (4000 suns).

Work Package 4: Nanostructures with improved quantum confinement enabled fabrication of brighter, more efficient LEDs for C-H and CO2 detection on GaAs substrates using new metamorphic buffer layers for widespread uptake. ULANC realised mid-infrared LEDs with internal efficiency of 10% , validated by GSS for gas sensors. NOTT discovered a new type of Zener tunnelling in InAsN/InAlAs diodes mediated by N-related zero-dimensional states. One highlight was the laser patterning of plasmonic structures with micrometer spatial resolution by dissociation of the N-H bond in hydrogenated In(As,N), enabling a new, compact, low-cost scalable technology for exploitation in security, environmental control, pharmaceuticals, etc. UM developed new techniques for bio-functionalization of III-V surfaces and surface-enhanced vibrational spectroscopy. By exploiting the change in refractive index upon oxidation the localized plasmon resonance of InAsSb:Si gratings on GaSb was tuned from 5 to 20 μm. In collaboration with Sikémia, the controlled chemical bonding of organic molecules to the III-V semiconductor surface by phosphonic acid chemistry led to new methods for bio-sensing to be patented.