Mid-infrared semiconductor lasers operating in the 2.0–5.0 μm spectral range play an important role for various applications, including trace-gas detection, biomedical analysis, and free-space optical communication. InP-based quantum-well (QW) and quantum-dash (Qdash) lasers are promising alternatives to conventional GaSb-based QW lasers because of their lower cost and mature fabrication infrastructure. However, they suffer from high threshold current density (Jth) and limited operation temperatures. InAs/InP quantum-dot (QD) lasers theoretically offer lower Jth owing to their three-dimensional carrier confinement. Nevertheless, achieving high-density, uniform InAs/InP QDs with sufficient gain for lasing over 2 μm remains a major challenge. Here, we report the first demonstration of mid-infrared InAs/InP QD lasers emitting beyond 2 μm. Five-stack InAs/In0.532Ga0.468As/InP QDs grown by molecular-beam epitaxy exhibit room-temperature photoluminescence at 2.04 μm. Edge-emitting lasers achieve lasing at 2.018 μm with a low Jth of 589 A cm−2 and a maximum operation temperature of 50 °C. Notably, the Jth per layer (118 A cm−2) is the lowest ever reported for room-temperature InP-based mid-infrared lasers, outperforming QW/Qdash counterparts. These results pave the way for a new class of low-cost, high-performance mid-infrared light sources using InAs/InP QDs, marking a notable step forward in the development of mid-infrared semiconductor lasers. Mid-infrared 2 μm InAs/InP quantum-dot lasers is first demonstrated, with a low threshold current density of 118 A cm−2 per layer and a maximum operating temperature of 50 °C.

Current progress in the scaling of continuous wave optical output power and conversion efficiency of broad-area GaAs-based edge emitters, broad-area lasers (BALs), operating in the 900 & mldr;1000 nm wavelength range is presented. Device research and engineering efforts have ensured that BALs remain the most efficient of all light sources, so that in the past 10 years, power conversion efficiency at 20 W continuous wave (CW) output power from BA lasers with a 90 & mldr;100 mu m wide stripe has increased 1.5-fold to 57% (via epitaxial layer design developments), whilst peak CW power per single emitter has increased around 3-fold to 70 W (via scaling of device size), with further scaling underway, for example via use of multi-junction designs. However, the peak achievable CW power conversion efficiency and CW specific output power (defined here as peak output power from a 100 mu m stripe diode lasers with a single p-n junction) has changed remarkably little, remaining around 70% and 25 W, respectively, for the past decade. Fortunately, research to understand the limits to peak efficiency and specific output power has also shown progress. Specifically, recent studies indicate that spatial non-uniformity in optical field and temperature play a major role in limiting both power and conversion efficiency. Technological efforts motivated by these discoveries to flatten lateral and longitudinal temperature profiles have successfully increased both power and efficiency. In addition, epitaxial layer designs with very high modal gain successfully reduce threshold current and increase slope at 25 degrees C to values comparable to those observed at 200 K, offering a path toward the 80% conversion efficiency range currently seen only at these cryogenic temperatures. Overall, whilst operating efficiency and power continue to scale rapidly, a technological path for increased specific power and peak efficiency is also emerging.

We present a new approach to quantum well laser design utilizing selectively-doped waveguides to enhance the efficiency and thermal stability of near- and mid-infrared lasers. For O-band lasers, we theoretically and experimentally assess the impact of this new approach on carrier recombination and Auger suppression.

We report on the key design factors for the development of Type-II 'W'-lasers for O-band (1260-1360 nm) applications. We investigate the effects of InGaAs and GaAsSb quantum well composition and thicknesses on the emission wavelength and recombination efficiency as well as of (Al, Ga) As barriers on optimum electrical and optical confinement. Photoluminescence (PL) tests structures and full device structures were fabricated and characterised. 1.25 mu m emitting lasers were demonstrated with a threshold current density and Jth values of 480 +/- 10 A cm-2 at 290 K, whereas 1.3 mu m lasers showed an increased Jth value of 5.5-7 kA cm-2 at 290 K. The PL test structures exhibited a similar trend with decreasing intensity with increasing wavelength. Gain measurements of the 1.3 mu m device demonstrate reasonably low optical losses of 10-15 cm-1 and a threshold modal gain of approximate to 25 cm-1.

Current temperature sensors require regular recalibration to maintain reliable temperature measurement. Photonic/quantum-based approaches have the potential to radically change the practice of thermometry through provision of in situ traceability, potentially through practical primary thermometry, without the need for sensor recalibration. This article gives an overview of the European Partnership in Metrology (EPM) project: Photonic and quantum sensors for practical integrated primary thermometry (PhoQuS-T), which aims to develop sensors based on photonic ring resonators and optomechanical resonators for robust, small-scale, integrated, and wide-range temperature measurement. The different phases of the project will be presented. The development of the integrated optical practical primary thermometer operating from 4 K to 500 K will be reached by a combination of different sensing techniques: with the optomechanical sensor, quantum thermometry below 10 K will provide a quantum reference for the optical noise thermometry (operating in the range 4 K to 300 K), whilst using the high-resolution photonic (ring resonator) sensor the temperature range to be extended from 80 K to 500 K. The important issues of robust fibre-to-chip coupling will be addressed, and application case studies of the developed sensors in ion-trap monitoring and quantum-based pressure standards will be discussed.

We undertake a comprehensive investigation of the temperature (T) and injection dependence of the modal gain in 1240 nm-emitting Type-II (GaIn)As/Ga(AsSb)/(GaIn)As "W" laser active regions for 25 <= T <= 300 K. From direct measurements of the short-wavelength transparency point, which serves as a proxy for population inversion, the behaviour of the maximum gain and peak blueshift are used to highlight the different temperature dependencies of the gain at different injection regimes. We show that the thermal redshift of the peak gain at room temperature reduces from 0.53 +/- 0.03 nm/ degree celsius under flat band conditions to 0.32 +/- 0.03 nm/ degree celsius at threshold. These results demonstrate the significant role of injection-dependent electrostatic effects and how it may be used through design to tailor the thermal properties of semiconductor lasers employing Type-II "W" active regions.

In-space laser power delivery provides a route to delivering energy to where it is most needed, for example, satellites or other space vehicles temporarily eclipsed from the sun or for lunar polar/planetary exploration whereby the target (e.g. a rover) may be in permanent darkness. High power edge-emitting semiconductor lasers are a promising light source for this application owing to their very high brightness, efficiency, and small physical size. However, their temperature dependence is complex and their output beam is highly asymmetric and divergent. Here, we show high efficiency and single mode operation over a wide range of temperatures using GaAs-based ridge waveguide (RW) lasers emitting at $\lambda=970 \mathrm{n}\mathrm{m}$. The vertical far-field divergence angle at 95% power content of the vertically collimated beam is also measured as ~6 mrad, which is good for power beaming system.

AbstractRecent demonstrations of room-temperature lasing in optically pumped GeSn show promise for future CMOS compatible lasers for Si-photonics applications. However, challenges remain for electrically pumped devices. Investigation of the processes that limit device performance is therefore vital in aiding the production of future commercial devices. In this work, a combined experimental and modelling approach is utilised to explore the dominant loss processes in current devices. By manipulating the band structure of functioning devices using high hydrostatic pressure techniques at low temperature, the dominant carrier recombination pathways are identified. This reveals that 93$$~\pm ~$$ ± 5% of the threshold current is attributable to defect-related recombination at a temperature, T = 85 K. Furthermore, carrier occupation of L-valley states (carrier leakage) is responsible for 1.1$$~\pm ~$$ ± 0.3% of the threshold current, but this sharply increases to 50% with a decrease of just 30 meV in the L-$$\Gamma$$ Γ separation energy. This indicates that thermal broadening of a similar order may reproduce these adverse effects, limiting device performance at higher temperatures. Temperature dependent calculations show that carrier occupation of indirect valley L-states strongly affects the transparency carrier density and is therefore very sensitive to the Sn composition, leading to an effective operational temperature range for given Sn compositions and strain values. Recommendations for future device designs are proposed based on band structure and growth optimisations.

A group IV-based laser offers the possibility of fully CMOS compatible growth of integrated circuits for Si photonics. In this work, we use hydrostatic pressure measurements and temperature-dependent band structure modelling to assess processes limiting the operational temperature in electrically injected GeSn lasers.

This paper reports on laser excitation power dependent photoluminescence (PL) studies on epitaxial GaAs1−xBix (2.3% < x < 10.4%) layers with thicknesses of 30–40 nm which are compressively strained onto GaAs substrates. Such materials when used as optical active regions in semiconductor lasers offer the possibility of suppressing the efficiency-limiting Auger recombination losses and improving laser performance in the telecommunication range (1.3–1.5 μm). These experimental investigations on GaAsBi allow us to verify the extent to which GaAs1−xBix provides the optimised band structure as predicted, and secondly to provide the first evidence of the influence of this band structure on optical efficiency and carrier recombination processes. An analysis of the dependence of PL intensity on excitation power was employed to identify the recombination mechanisms in GaAs1−xBix alloys. Temperature tuning the samples with bismuth concentration ~ 8.5% and 1.4% provides tentative evidence for the suppression of Auger recombination losses in this material system highlighting its potential for efficient telecoms laser applications.

In this paper we discuss the emerging applications of photovoltaics for laser-based optical wireless power transfer. In particular, we focus on how key factors impact the design of the system, including wavelength, power range, operating temperature and environment and their impact on the choice of laser and photovoltaic cells. Two examples are considered: the first using bespoke InP-based photovoltaics targeting 1550 nm operation for eye-safe terrestrial applications, and the second concerning the use of visible and near-IR laser illumination of solar cells for satellites in low Earth orbit. The challenges and opportunities associated with each application will be discussed.

Light-emitting diodes (LEDs) are ubiquitous in modern society, with applications spanning from lighting and displays to medical diagnostics and data communications. Metal-halide perovskites are promising materials for LEDs because of their excellent optoelectronic properties and solution processability. Although research has progressed substantially in optimizing their external quantum efficiency, the modulation characteristics of perovskite LEDs remain unclear. Here we report a holistic approach for realizing fast perovskite photonic sources on silicon based on tailoring alkylammonium cations in perovskite systems. We reveal the recombination behaviour of charged species at various carrier density regimes relevant for their modulation performance. By integrating a Fabry–Pérot microcavity on silicon, we demonstrate perovskite devices with efficient light outcoupling. We achieve device modulation bandwidths of up to 42.6 MHz and data rates above 50 Mbps, with further analysis suggesting that the bandwidth may exceed gigahertz levels. The principles developed here will support the development of perovskite light sources for next-generation data-communication architectures. The demonstration of solution-processed perovskite emitters on silicon substrates also opens up the possibility of integration with micro-electronics platforms. Tailoring the composition of organic cations enables manipulating the recombination rates of perovskites. Optimized solution-processed perovskite emitters fabricated on silicon exhibit up to 42.6-MHz modulation bandwidth and 50-Mbps data rate.

In this paper we discuss how a combination of band structure and band alignment engineering may be used to reduce the temperature sensitivity of semiconductor lasers operating in the near-IR. The use of back-to-back type-II band alignment “W”-structures, already successfully demonstrated in the mid-IR, provides a route to engineer the temperature sensitivity of the emission wavelength in near-IR devices through control of the band gap and band bending. Furthermore, utilising novel alloys such as the bismide-nitrides also provides a route to reduce non-radiative processes which underpin the temperature sensitivity of the threshold current across this wavelength range.

We investigate the temperature-dependence of modal gain for type-II (GaIn)As/Ga(AsSb) “W”-laser structures operating around the O-band. Measurements show their potential to control the temperature dependence of the gain due to carrier-induced band bending effects. This is of interest to semiconductor laser and optical amplifier applications.

Auger recombination is known to be a significant non-radiative process limiting near- and mid-infrared quantum well lasers. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) permits two fundamentally different categories of Auger mechanisms to operate. These mechanisms may be identified as either activated or thresholdless in nature. In this work, we investigate the nature of the dominant Auger mechanism in mid-infrared emitting quantum wells by characterizing a range of type-I InGaAsSb quantum well lasers operating within the 2 - 3 μm wavelength range. The temperature dependence of both the threshold current density and integrated spontaneous emission reveal that the threshold current is dominated by radiative recombination up to a break-point temperature (occurring below 200 K). Beyond the break point temperature, the exponential dependence of the threshold current increases rapidly. The deterioration in the stability of lasing threshold indicates that a thermally activated Auger process is dominant in all devices and is sensitive to the population of heavy-holes in the quantum wells.

Over the last decade, 2,2″,7,7″‐Tetrakis[ N , N ‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) has remained the hole transporting layer (HTL) of choice for producing high efficiency perovskite solar cells (PSCs). However, PSCs incorporating spiro‐OMeTAD suffer significantly from dopant induced instability and non‐ideal band alignments. Herein, a new approach is presented for tackling these issues using the functionality of organometallocenes to bind to Li + dopant ions, rendering them immobile and reducing their impact on the degradation of PSCs. Consequently, significant improvements are observed in device stability under elevated temperature and humidity, conditions in which ion migration occurs most readily. Remarkably, PSCs prepared with ferrocene retain 70% of the initial power conversion efficiency (PCE) after a period of 1250 h as compared to only 8% in the control. Synergistically, it is also identified that ferrocene improves the hole extraction yield at the HTL interface and reduces interfacial recombination enabling PCEs to reach 23.45%. This work offers a pathway for producing highly efficient spiro‐OMeTAD devices with conventional dopants via addressing the key challenge of dopant induced instability in leading PSCs.

We describe the use of a modified QW structure to achieve temperature stability in O-band lasers. We show the potential for temperature insensitivity of threshold from -40 to $+80{\ }^{\circ}\mathrm{C}$ in an InGaAsP/InP structure. Such devices are of interest for lower energy consuming datacomms systems.

Successful manipulation of halide perovskite surfaces is typically achieved via the interactions between modulators and perovskites. Herein, it is demonstrated that a strong‐interaction surface modulator is beneficial to reduce interfacial recombination losses in inverted (p‐i‐n) perovskite solar cells (IPSCs). Two organic ammonium salts are investigated, consisting of 4‐hydroxyphenethylammonium iodide and 2‐thiopheneethylammonium iodide (2‐TEAI). Without thermal annealing, these two modulators can recover the photoluminescence quantum yield of the neat perovskite film in contact with fullerene electron transport layer (ETL). Compared to the hydroxyl‐functionalized phenethylammonium moiety, the thienylammonium facilitates the formation of a quasi‐2D structure onto the perovskite. Density functional theory and quasi‐Fermi level splitting calculations reveal that the 2‐TEAI has a stronger interaction with the perovskite surface, contributing to more suppressed non‐radiative recombination at the perovskite/ETL interface and improved open‐circuit voltage ( V OC ) of the fabricated IPSCs. As a result, the V OC increases from 1.11 to 1.20 V (based on a perovskite bandgap of 1.63 eV), yielding a power conversion efficiency (PCE) from ≈20% to 21.9% (stabilized PCE of 21.3%, the highest reported PCEs for IPSCs employing poly[ N , N ′′‐bis(4‐butylphenyl)‐ N , N ′′‐bis(phenyl)benzidine] as the hole transport layer, alongside the enhanced operational and shelf‐life stability for unencapsulated devices.