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.

Future expansion of computing capabilities relies on a reduction of energy consumption in silicon-based integrated circuits. A promising solution is to replace electrical wires with optical connections, for which a key component is a nanolaser that coherently emits into silicon-based waveguides to route information across a chip, in place of bulky off-chip devices. We report room temperature, sub-μm 2 footprint, quantum-well-in-nanopillar lasers grown directly on silicon and silicon-on-insulator (SOI) substrates that emit within the silicon-transparent wavelength range under optical excitation. The laser wavelength is controlled by changing the InGaAs quantum well thickness and alloy composition, quite independent of lattice mismatch with the InP barrier, a unique property of the 3D core-shell growth mode. We achieve excellent luminescence yield and low continuous wave transparency power due to the well-passivated InGaAs/ InP interfaces. These sub-μm 2 footprint long-wavelength lasers could enable optoelectronic integration and photon routing with silicon waveguides on the technologically relevant SOI platform.

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 VOC 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.

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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.

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, lowtemperature 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 sitecontrolled growth and electrically driven long-wavelength emission make the InP nano-LED an ideal component in advanced photonic integrated circuits.

A hybrid Monte Carlo-density matrix transport simulator is used to analyze the transport properties of resonant-phonon type terahertz quantum cascade lasers. By comparing calculated and experimental results, the importance of stimulated emission to the interpretation of experimental data is highlighted, particularly for devices based on diagonal radiative transitions. Finally, we discuss the absence of mode competition effects on transport.

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