Additive manufacturing promises enormous geometrical freedom and the potential to combine materials for complex functions. The speed, geometry, and surface quality limitations of additive processes ...are linked to their reliance on material layering. We demonstrated concurrent printing of all points within a three-dimensional object by illuminating a rotating volume of photosensitive material with a dynamically evolving light pattern. We printed features as small as 0.3 millimeters in engineering acrylate polymers and printed soft structures with exceptionally smooth surfaces into a gelatin methacrylate hydrogel. Our process enables us to construct components that encase other preexisting solid objects, allowing for multimaterial fabrication. We developed models to describe speed and spatial resolution capabilities and demonstrated printing times of 30 to 120 seconds for diverse centimeter-scale objects.
Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials ...with high absorption coefficients are particularly promising for photodetection in energy-efficient optical links because of the potential to scale down the absorber size, and the resulting capacitance and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar junction phototransistor with a high current gain (53.6), bandwidth (7 GHz) and responsivity (9.5 A/W) using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The quantum efficiency-bandwidth product of 105 GHz is the highest for photodetectors on silicon. The bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
Volumetric additive manufacturing (VAM) promises a significantly improved regime of capabilities for 3D printing. Computed Axial Lithography (CAL) is a photopolymerization-based tomographic VAM ...process which constructs objects by projecting systematic illumination patterns into a container of photosensitive prepolymer as it rotates. This technique is used to demonstrate the manufacturing of parts that faithfully adhere to respective target geometries. A principled optimization approach is used to generate the illumination patterns by penalizing 3D dose constraint violations and is demonstrated to achieve better performance than a heuristic dose matching technique. 3D objects are experimentally fabricated using CAL, and excellent fidelity to target design is demonstrated on diverse exemplary geometries. Imperfections between design and resulting print are experimentally characterized using laser scanning measurements. Deviations below 1.05 mm are achieved (max standard deviation = 0.22 mm, absolute max mean deviation = 0.15 mm) on complex objects with extent of 20–40 mm that are all fabricated volumetrically in minutes.
Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single nanopillar ...photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a novel regrown core–shell p-i-n junction to improve device performance by eliminating shunt current paths, resulting in a high V OC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced broadband light absorption is also demonstrated over a wide spectral range of 400–800 nm.
Highly compact III–V compound semiconductor active nanophotonic devices integrated with silicon are important for future low power optical interconnects. One approach toward realizing heterogeneous ...integration and miniaturization of photonic devices is through nanowires/nanopillars grown directly on silicon substrates. However, to realize their full potential, the integration of nanowires/nanopillars with silicon-based electronics must be made scalable via precise control of nanopillar site and dimensions. Here we demonstrate the first electrical-pumped InGaAs/InP multiquantum-well (MQW) light emitting diodes (LED) using nanopillar array directly grown on a Si substrate with site control, with current conduction directly through the silicon. The growth is via catalyst-free, low-temperature metal organic chemical vapor deposition, which is CMOS compatible. We report excellent optical properties including long minority carrier lifetimes and room-temperature lasing under optical pumping. InGaAs/InP quantum wells are incorporated in the nanopillars in a core–shell growth mode, to obtain silicon transparent emission of ∼1510 nm with high internal quantum efficiency (∼30%). Despite its small footprint, a high output power (4 μW) was measured, and the device could be electrically biased to produce optical gain. CMOS-compatible site-controlled growth and electrically driven long-wavelength emission make the InP nano-LED an ideal component in advanced photonic integrated circuits.
We present a new platform based on suspended III-V semiconductor nanopillars for direct integration of optoelectronic devices on a silicon substrate. Nanopillars grown in core-shell mode with ...InGaAs/InP quantum wells can support long-wavelength Fabry-Pérot resonances at room temperature with this novel configuration. Experimental results are demonstrated at a silicon-transparent wavelength of 1460 nm, facilitating integration with silicon platform.
III-V optoelectronic device integration in a CMOS post-process compatible manner is important for the intimate integration of silicon-based electronic and photonic integrated circuits. The low ...temperature, self-catalyzed growth of high crystalline quality Wurtzite-phase InP nanopillars directly on silicon presents a viable approach to integrate high performance nano-optoelectronic devices. For the optical transmitter side of the photonic link, InGaAs quantum wells have been grown in a core-shell manner within InP nanopillars. Position-controlled growth with varying pitch is used to systematically control emission wavelength across the same growth substrate. These nanopillars have been fabricated into electrically-injected quantum well in nanopillar LEDs operating within the silicon transparent 1400–1550 nm spectral window and efficiently emitting micro-watts of power. A high quality factor (Q ~ 1000) undercut cavity quantum well nanolaser is demonstrated, operating in the silicon-transparent wavelength range up to room temperature under optical excitation. We also demonstrate an InP nanopillar phototransistor as a sensitive, low-capacitance photoreceiver for the energy-efficient operation of a complete optical link. Efficient absorption in a compact single nanopillar InP photo-BJT leads to a simultaneously high responsivity of 9.5 A/W and high 3dB-bandwidth of 7 GHz. For photovoltaic energy harvesting, a sparsely packed InP nanopillar array can absorb ~90% of the incident light because of the large absorption cross section of these near-wavelength nanopillars. Experimental data based on wavelength and angle resolved integrating sphere measurements will be presented to discuss the nearly omnidirectional absorption properties of these nanopillar arrays.
We propose a platform based on III−V compound semiconductor nanopillars monolithically integrated with silicon photonics. Nanopillars were grown in a process free of metal catalysts onto silicon at ...low temperature, and a bottom-up process was applied to define the photonic integrated circuit. Stimulated and spontaneous emissions from the nanopillars are direct coupled to silicon waveguides.
We demonstrate InP nanopillar bipolar junction phototransistors monolithically integrated on a Silicon substrate. With a responsivity of 4 A/W and bandwidth of 7.5 GHz, these receivers indicate a ...route towards efficient on-chip optical interconnects.
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