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Breakthroughs in nanomaterials and nanoscience enable the development of novel photonic devices and systems ranging from the automotive sector, quantum cryptography to metropolitan area and access networks. Geometrical architecture presents a design parameter of device properties. Self-organization at surfaces in strained heterostructures drives the formation of quantum dots (QDs). Embedding QDs in photonic and electronic devices enables novel functionalities, advanced energy efficient communication, cyber security, or lighting systems. The recombination of excitons shows twofold degeneracy and Lorentzian broadening. The superposition of millions of excitonic recombinations from QDs in real devices leads to a Gaussian envelope. The material gain of QDs in lasers is orders of magnitude larger than that of bulk material and decoupled from the index of refraction, controlled by the properties of the carrier reservoir, thus enabling independent gain and index modulation. The threshold current density of QD lasers is lowest of all injection lasers, is less sensitive to defect generation, and does not depend on temperature below 80°C. QD lasers are hardly sensitive to back reflections and exhibit no filamentation. The recombination from single QDs inserted in light emitting diodes with current confining oxide apertures shows polarized single photons. Emission of ps pulses and date rates of 10 +bit upon direct modulation benefits from gain recovery within femtoseconds. Repetition rates of several 100 GHz were demonstrated upon mode-locking. Passively mode-locked QD lasers generate hat-like frequency combs, enabling Terabit data transmission. QD-based semiconductor optical amplifiers enable multi-wavelength amplification and switching and support multiple modulation formats.

Understanding the carrier dynamics of nanostructures is the key for development and optimization of novel semiconductor nano-devices. Here, we study the optical properties and carrier dynamics of (InGa)(AsSb)/GaAs/GaP quantum dots (QDs) by means of non-resonant energy and time-resolved photoluminescence depending on temperature. Studying this material system is fundamental in view of the ongoing implementation of such QDs for nano memory devices. The structures studied in this work include a single QD layer, QDs overgrown by a GaSb capping layer, and solely a GaAs quantum well, respectively. Theoretical analytical models allow to discern the common spectral features around the emission energy of 1.8 eV related to the GaAs quantum well and the GaP substrate. We observe type-I emission from QDs with recombination times between 2 ns and 10 ns, increasing towards lower energies. Moreover, based on the considerable tunability of the QDs depending on Sb incorporation, we suggest their utilization as quantum photonic sources embedded in complementary metal-oxide-semiconductor platforms, due to the feasibility of a nearly defect-free growth of GaP on Si. Finally, our analysis confirms the nature of the pumping power blue-shift of emission originating from the charged-background induced changes of the wavefunction spatial distribution.

We investigated metal-organic vapor phase epitaxy grown (InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots (QDs) with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography (APT). The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution, which provides detailed structural and compositional information on the system. The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our sample with a very high density of ∼4 × 1011 cm−2. APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb. Finite element (FE) simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface. The composition of the QDs is estimated by combining the results from X-STM and the FE simulations, yielding ∼InxGa1 − xAs1 − ySby, where x = 0.25–0.30 and y = 0.10–0.15. Noticeably, the reported composition is in good agreement with the experimental results obtained by APT, previous optical, electrical, and theoretical analysis carried out on this material system. This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed. A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer, where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation. Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.

The current progress of energy-efficient high-speed VCSELs based on GaAs substrates is presented. Novel approaches for the design of VCSELs are presented, potentially leading to larger bandwidth bit rates and lower power consumption. The first approach is based on the optimization of the VCSEL photon lifetime. The second one introduces a novel design based on oxidizing the apertures from multiple etched holes of varying geometries. These designs are also essential for improving the energy efficiency of future modules by optimizing the match of the electronic driver and the photonic device.

Single-mode long-wavelength (LW) vertical-cavity surface-emitting lasers (VCSELs) present an inexpensive alternative to DFB-lasers for data communication in next-generation giga data centers, where optical links with large transmission distances are required. Narrow wavelength-division multiplexing systems demand large bit rates and single longitudinal and transverse modes. Spatial division multiplexing transmission through multicore fibers using LW VCSELs is enabling still larger-scale data center networks. This review discusses the requirements for achieving high-speed modulation, as well as the state-of-the-art. The hybrid short-cavity concept allows for the realization of f3dB frequencies of 17 GHz and 22 GHz for 1300 nm and 1550 nm range VCSELs, respectively. Wafer-fusion (WF) concepts allow the realization of long-time reliable LW VCSELs with a record single-mode output power of more than 6 mW, 13 GHz 3 dB cut-off frequency, and data rates of 37 Gbit/s for non-return-to-zero (NRZ) modulation at 1550 nm.

Although semiconductor excitons consist of a fermionic subsystem (electron and hole), they carry an integer net spin similar to Cooper-electron-pairs. While the latter cause superconductivity by forming a Bose–Einstein-condensate, excitonic condensation is impeded by, for example, a fast radiative decay of the electron-hole pairs. Here, we investigate the behaviour of two electron-hole pairs in a quantum dot with wurtzite crystal structure evoking a charge carrier separation on the basis of large spontaneous and piezoelectric polarizations, thus reducing carrier overlap and consequently decay probabilities. As a direct consequence, we find a hybrid-biexciton complex with a water molecule-like charge distribution enabling anomalous spin configurations. In contrast to the conventional-biexciton complex with a net spin of s =0, the hybrid-biexciton exhibits s =±3, leading to completely different photoluminescence signatures in addition to drastically enhanced charge carrier-binding energies. Consequently, the biexcitonic cascade via the dark exciton can be enhanced on the rise of temperature as approved by photon cross-correlation measurements. Artificial atoms usually constitute an orbital structure for trapped charge carriers. Here, Hönig et al . demonstrate that polarization fields and large charge carrier masses can dilute the common orbital conception and find a hybrid-biexciton molecule that enables anomalous spin configurations.

We report on the progress made in the development of 1550 nm vertical-cavity surface-emitting lasers (VCSELs) for data transmission applications. These lasers were grown using molecular beam epitaxy and manufactured through wafer fusion. Such devices exhibit high speed and high optical output power, benefitting from GaAs-based mirrors and an InP-based active region. We investigate their static and dynamic performance in order to optimize for long-distance fiber-optic communication. We achieved record data rates of 40 Gbps across 1 m single-mode optical fiber with a single-mode power exceeding 3.8 mW by using signal pre-emphasis. Long-distance tests show, that these VCSELs are capable of transmitting more than 27 Gbps across a 2 km single-mode fiber, and can achieve as low as 600 fJ energy consumption per bit transferred.

The review is focused on reporting about design optimizations of the long-wavelength (LW) vertical-cavity surface-emitting laser (VCSELs) with an aperture formed by regrown (buried) tunnel junctions, pioneered by Amann et al from the Technical University of Munich and Vertilas GmbH. Ultra-low-cost solutions for the above 10 Gbps data rates were realized for a short-cavity (SC) design (with one semiconductor and one dielectric mirror) intended for the 1300–1550 nm range. A modified SC design was also used for 2D VCSEL arrays applied as a short wave infrared illuminator. Cost-effective ultra-high modulation rates (larger than 40 Gbps) were realized for the ultra SC design (with hybrid and dielectric mirrors), suitable for telecommunication and datacom. Since the current tuning range of LW VCSELs is significantly larger than that of distributed feedback edge-emitting lasers, Amann et al developed SC InP-based VCSELs design dedicated for gas detection (in the 1.8–2.3 μ m range). Tunable micro-electromechanical systems VCSELs have also been employed, as well as GaSb-based VCSELs. The latter ones are presently limited in use due to their low modal gain in the VCSEL geometry. The design of 1300–1550 nm wafer-fused (WF) VCSELs grown by metal-organic chemical vapor deposition was primarily developed by Kapon et al from the Swiss Federal Institute of Technology/BeamExpress SA. This approach allowed full-wafer processing and met Telcordia compliant qualifications. The design of WF VCSELs grown by industrial molecular-beam epitaxy has been implemented by the team of the present authors and demonstrated promising applications for intra-data-center connections. Trumpf Photonic Components announced the mass production of InP-based VCSELs above 1300 nm. Sony Semiconductor Solutions Corporation has been demonstrated 1380 nm range WF VCSELs. InP-based VCSELs design from Corning Inc. can also be adopted for under organic light-emitting diode display applications or as a short wave infrared illuminator.

Record energy efficiency of 97 fJ bit −1 of 940 nm single mode VCSELs for four level pulse amplitude modulation at 100 Gbps across 100 meters of OM5 multimode lensed fiber at 25 °C is demonstrated. This value is, to the best of our knowledge, the best energy efficiency at such large modulation rates and distances reported in literature so far. As compared to previous VCSEL designs of us, the number and the design of the mirrors and quantum wells are optimized and the peak gain/ distributed Bragg reflectors max transmission is set to −15 nm. Employing these VCSELs in next generation data centers will reduce considerably their power budget, which is controlled by the energy efficiency of the optical interconnects.