Mid-infrared (MIR) silicon photonics holds the potential for realizing next generation ultracompact spectroscopic systems for applications in gas sensing, defense, and medical diagnostics. The direct epitaxial growth of antimonide-based compound semiconductors on silicon provides a promising approach for extending the wavelength of silicon photonics to the longer infrared range. This paper reports on the fabrication of a high performance MIR photodetector directly grown onto silicon by molecular beam epitaxy. The device exhibited an extended cutoff wavelength at ∼5.5 μm and a dark current density of 1.4 × 10–2 A/cm2 under 100 mV reverse bias at 200 K. A responsivity of 0.88 A/W and a specific detectivity in the order of 1.5 × 1010 Jones was measured at 200 K under 100 mV reverse bias operation. These results were achieved through the development of an innovative structure which incorporates a type-II InAs/InAsSb superlattice-based barrier nBn photodetector grown on a GaSb-on-silicon buffer layer. The difficulties in growing GaSb directly on silicon were overcome using a novel growth procedure consisting of an efficient AlSb interfacial misfit array, a two-step growth temperature procedure and dislocation filters resulting in a low defect density, antiphase domain free GaSb epitaxial layer on silicon. This work demonstrates that complex superlattice-based MIR photodetectors can be directly integrated onto a Si platform, which provides a pathway toward the realization of new, high performance, large area focal plane arrays and mid-infrared integrated photonic circuits.

Silicon photonics has emerged as the most promising technology for nextgeneration compact optoelectronic systems, but further development is still required to achieve efficient and reliable on-chip light sources. Direct epitaxial growth of antimonidebased compound semiconductor materials on silicon provides a pathway toward the monolithic integration of new, mid-infrared solid-state light sources and comprehensive photonic circuits on silicon platforms. Such devices have wide-ranging applications in environmental monitoring and medical diagnostics. This paper reports on the realization of a mid-infrared InAsSb light emitting diode directly integrated onto silicon using molecular beam epitaxy. The heteroepitaxial integration of the InAsSb p-in device onto silicon was achieved with the use of a novel, antiphase domain-free, GaSb-on-silicon buffer layer. The device exhibited efficient light emission at room temperature, peaking at around 4.5 μm, which corresponds well to the CO 2 atmospheric absorption band. An output power of 6 μW and an external quantum efficiency of 0.011% was measured at 300 K. These results demonstrate midinfrared III-V light emitting diodes can be directly grown on silicon, which is an essential step towards the realization of the next generation, on-chip integrated light sources.

GaSb-based materials can be used to produce high performance photonic devices operating in the technologically important mid-infrared spectral range. Direct epitaxial growth of GaSb on silicon (Si) is an attractive method to reduce manufacturing costs and opens the possibility of new applications, such as lab-on-a-chip MIR photonic integrated circuits and monolithic integration of focal plane arrays (FPAs) with Si readout integrated circuits (ROICs). However, fundamental material dissimilarities, such as the large lattice mismatch, polar-nonpolar character of the III-V/Si interface and differences in thermal expansion coefficients lead to the formation of threading dislocations and antiphase domains, which effect the device performance. This work reports on the molecular beam epitaxial growth of high quality GaSb-based materials and devices onto Si. This was achieved using a novel growth procedure consisting of an efficient AlSb interfacial misfit array, a two-step GaSb growth temperature procedure and a series of dislocation filter superlattices, resulting in a low defect density, anti-phase domain free GaSb buffer layer on Si. A nBn barrier photodetector based on a type-II InAs/InAsSb superlattice was grown on top of the buffer layer. The device exhibited an extended 50 % cutoff wavelength at 5.40 μm at 200 K which moved to 5.9 μm at 300 K. A specific detectivity of 1.5 x10 10 Jones was measured, corresponding in an external quantum efficiency of 25.6 % at 200 K.

There have been relatively few reports of lasing from InSb quantum dots (QDs). In this work, type II InSb/InAs QD laser diodes emitting in the mid-infrared at 3.1 μm have been demonstrated and characterized. The gain was determined to be 2.9 cm−1 per QD layer, and the waveguide loss was ∼15 cm−1 at 4 K. Spontaneous emission measurements below threshold revealed a blue shift of the peak wavelength with increasing current, indicating filling of ground state heavy hole levels in the QDs. The characteristic temperature, T0 = 101 K below 50 K, but decreased to 48 K at higher temperatures. The emission wavelength of these lasers showed first a blue shift followed by a red shift with increasing temperature. A hybrid structure was used to fabricate the laser by combining a liquid phase epitaxy grown p-InAs0.61Sb0.13P0.26 lower cladding layer and an upper n+ InAs plasmon cladding layer which resulted in a maximum operating temperature (Tmax) of 120 K in pulsed mode, which is the highest reported to date.

In England, nursing education and training is currently undergoing a fundamental change in terms of its delivery and funding. While the debate regarding the loss of the National Health Service (NHS) bursary rages on, albeit with ministers occluding their ears firmly with their fingers, one aspect of government policy that has been off the mainstream agenda for some time is that of the Nurse Associate (NA). However, last month a debate at London Southbank University (LSBU) kicked it back from long grass and into our living roomsnot just figuratively but literally, if you live-streamed the event via Periscope and Twitter. In this paper I will discuss the positions of those involved in the debate from my own perspective-as an undergraduate student nurse currently studying at King's College London. The concept of the NA is not a new one. In fact, many NHS trusts currently employ individuals in similar roles but under the guise of different job titles (Cavendish, 2013). This convolutes the debate and leads to confusion as to what will and will not become part of the role nationally, but streamlining and formalising the training of such positions would seemingly be a sensible strategy and is advocated within Health Education England's (HEE) Shape of Caring Review (HEE, 2015). However, as with many new initiatives, while admirable and well-meaning, it is the unintended consequences that are often overlooked. Like all nursing students, I have been encouraged to 'look for the evidence', 'question' and 'critique', and LSBU's debate was very much part of this process for me. Chaired by Professor Warren Turner, the Dean and Pro-Vice Chancellor of LSBU's School of Health and Social Care, and with Professor Leslie Baillie posing the pro-NA position and Dr Elaine Maxwell opposing, the event finally swayed my allegiance firmly into one camp.