The technology of 3D bioprinting has gained significant interest in biomedical engineering, regenerative medicine, and the pharmaceutical industry. Providing a new scope in tissue and organ printing, 3D bioprinters are becoming commercialized for biological processes. However, the current technology is costly, ranging from USD$9,000-$30,000 and is limited to customized extrusion methods. Multiple microfluidic pump systems for bioink extrusion are commercially available at USD$30,000. Additionally, the use of Cartesian systems for 3D printing restricts the user to three axes of movement and makes multi-material modeling a challenge. Consequently, it was proposed to design a cost effective robotic 3D bioprinting system, compatible with peptide bioinks which were developed at KAUST Laboratory for Nanomedicine. The components of the system included a programmable robotic arm, an extruder for bioprinting, and multiple microfluidic pumps. The extruder was designed using a coaxial nozzle made of three inlets and one outlet. The programmable microfluidic pumps transported the peptide bioink, phosphate buffer saline (PBS) and human skin fibroblast cells (in cell culture media solution) through the nozzle to extrude a peptide nanogel thread. Model cell structures were printed and monitored for a period of two weeks and subsequently found to be alive and healthy. The system was kept well under a budget of USD$3,500. Future modifications of the current system will include adding a custom bioprinting arm to allow multi-material printing which can fully integrate and synchronize between the pumps and the robotic arm. This system will allow the production of a more advanced robotic arm-based 3D bioprinting system in the future.
In this paper, a thermally induced dielectric strain on quantum well intermixing (QWI) technique is employed on tensilestrained InGaP/InAlGaP laser structure, to promote inter-diffusion, in conjunction with cycle annealing at elevated temperature. A bandgap blueshift as large as large as ~250meV was observed for samples capped with a single and bilayer of the dielectric film (1μm-SiO2 and 0.1μm-Si3N4) and annealed at a high temperature (700-1000oC) for cycles of annealing steps. Samples subjected to this novel QWI technique for short duration and multiple cycle annealing steps shown a high degree of intermixing while maintaining strong photoluminescence (PL) intensity, narrow full wave at half maximum (FWHM) and good surface morphology. Laser devices fabricated using this technique, lased at a wavelength of 608nm with two facet power of ~46mW, indicating the high quality of the material. Our results show that thermal stress can be controlled by the engineering dielectric strain opening new perspectives for QWI of photonics devices.
We report a simultaneous amplified emission from InAs-based self-assembled quantum dot and quantum well in a multistack dot-in-a-well superluminescent light-emitting diode (SLD) for application in broadband sources. A combination of atomic force microscopy, photoluminescence of the test structures, and optoelectronic characterization of SLD is used to obtain an emission bandwidth of ∼292 nm covering O–S communication band (including 850-nm band) and a maximum continuous power of ∼1.33 mW at room temperature.
We achieved considerable laser diode (LD) improvement after annealing InGaP/InAlGaP laser structure at 950°C for a total annealing time of 2 min. The photoluminescence intensity is increased by 10 folds and full-wave at half-maximum is reduced from ∼30 to 20 nm. The measured LDs exhibited significantly reduced threshold current (Ith), from 2 to 1.5 A for a 1-mm long LD, improved internal efficiency (ηi), from 63% to 68%, and increased internal losses αi, from 14.3 to 18.6 cm−1. Our work suggests that the use of strain-induced quantum well intermixing is a viable solution for high-efficiency AlGaInP devices at shorter wavelengths. The advent of laser-based solid-state lighting (SSL) and visible-light communications (VLC) highlighted the importance of the current findings, which are aimed at improving color quality and photodetector received power in SSL and VLC, respectively, via annealed red LDs.
We increased the Al content in the single quantum well InGaP/InAlGaP laser by strain-induced quantum well intermixing, and obtained a considerable enhancement (close to ten-fold increase) in the photoluminescence (PL) intensity. Among the annealing process investigated, we achieved lasing at 638 nm in conjunction with reduction in the lasing threshold current by close to 500 mA in a moderately intermixed laser. Lasing in orange color, as well as spontaneous emission in the yellow and green color regime, were also achieved by extending the annealing conditions. The significance of the current work became apparent when one considers that achieving these tunable wavelengths by increasing the Al content in quantum wells during epitaxy growth leads to severe lattice-mismatch and poor material quality. Hence, our Al "drive-in" intermixing process is a viable approach for forming Al-rich InAlGaP quantum well, which is essential for realizing efficient optoelectronic devices in the "green-yellow-orange gap".
In this paper, a novel strain-induced quantum well intermixing (QWI) technique is employed on InGaP/InAlGaP material system to promote interdiffusion via application of a thick-dielectric encapsulant layer, in conjunction with cycle
annealing at elevated temperature. Broad area devices fabricated from this novel cost-effective QWI technique lased at
room-temperature at a wavelength as short as 608nm with a total output power of ~46mW. This is the shortest-
wavelength electrically pumped visible semiconductor laser, and the first report of lasing action yet reported from post-
growth interdiffused process. Furthermore, we also demonstrate the first yellow superluminescent diode (SLD) at a
wavelength of 583nm with a total two-facet output power of ~4.5mW - the highest optical power ever reported at this wavelength in this material system. The demonstration of the yellow SLD without complicated multiquantum barriers to
suppress the carrier overflow will have a great impact in realizing the yellow laser diode.
We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO2 and Si3N4 films, HfO2 and SrTiO3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO2 capped sample. Likewise, investigation of TiO2, Al2O3, and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ∼1060─1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green–yellow–orange coherent light generation, as well as addressing photonic integration via area-selective, and postgrowth bandgap engineering.
Semiconductor nanostructures have generated tremendous scientific interests as well as practical applications stemming from the engineering of low dimensional physics phenomena. Unlike 0D and 1D nanostructures, such as quantum dots and nanowires, respectively, 2D structures, such as nanomembranes, are unrivalled in their scalability for high yield manufacture and are less challenging in handling with the current transfer techniques. Furthermore, due to their planar geometry, nanomembranes are compatible with the current complementary metal oxide semiconductor (CMOS) technology. Due to these superior characteristics, there are currently different techniques in exfoliating nanomembranes with different crystallinities, thicknesses and compositions. In this work we demonstrate a new facile technique of exfoliating gallium nitride (GaN) nanomembranes with novel features, namely with the non-radiative cores of their threading-dislocations (TDs) being etched away. The exfoliation process is based on engineering the gallium vacancy (VGa) density during the GaN epitaxial growth with subsequent preferential etching. Based on scanning and transmission electron microscopies, as well as micro-photoluminescence measurements, a model is proposed to uncover the physical processes underlying the formation of the nanomembranes. Raman measurements are also performed to reveal the internal strain within the nanomembranes. After transferring these freely suspended 25 nm thin GaN nanomembranes to other substrates, we demonstrate the temperature dependence of their bandgap by photoluminescence technique, in order to shed light on the internal carrier dynamics.
In this paper we report on the multi-section gain and absorption analysis of strain engineered molecular beam epitaxy
(MBE) grown GaAs and InGaAs capped bilayers. The InGaAs capped bilayer quantum dot (QD) lasers extends the
room temperature lasing wavelength to 1.45 μm. The spectral measurement of gain demonstrates that net modal gain is
achieved beyond 1.5 μm at room temperature. Analysis of the temperature and current density dependence gain
characteristics of a GaAs capped bilayer sample indicate that the temperature sensitivity of threshold current around
room temperature is due to phonon assisted thermal escape of carriers from the QDs.
Quantum Dot lasers exhibit the novel phenomenon of dual state lasing where population inversion can be achieved on
two optical transitions within the dots. In principle this might occur if a phonon bottleneck exists to impede relaxation of
carriers from the higher energy state. Here we present an alternative explanation whereby different lasing modes
compete for carriers and are spatially separable. Evidence comes from a comparison of electrical and optical
measurements made on the devices. The evolution of a particular lasing mode depends on diffusion of carriers between
dots and we show how, using an equivalent circuit model, this is consistent with our measurements.
In this paper a multiple description coding (MDC) that uses more than one multiple description scalar quantizer
(MDSQ) is presented. The MDSQ merging constraints for joint decoding of descriptions obtained using side
quantizers from different MDSQs are presented. In this way, the bit streams from the side quantizers resulting
in significantly different rate-distortion properties are jointly decoded as opposed to that of two bit streams
of similar rate-distortion performances obtained using a single MDSQ. Rate distortion performances of joint
decoding of different description combinations obtained from multiple MDSQs outperforms those obtained from
a single MDSQ. Robustness of the proposed approach evaluated under packet erasure channel is higher than
that of the conventional approach. In addition to high robustness, we also demonstrate how this scheme is
extended to successive side quantizer bin merging that is used to achieve robust quality scalability within an
MDC framework.
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