Integrated Multi-Color Light Emitting Device Made With Hybrid Crystal Structure

III-nitride devices are commonly made on sapphire substrates today for various commercial electronic and optoelectronic applications. Thus, this innovation relates directly to the combination of devices on opposite sides of the sapphire substrate. One possible device combination is to have LEDs one side and solar cells on the other, such as for displays.

The new fabrication method is an electron lithography scheme enabling monolithic integration of multiple photonic devices on a single PIC. The technology was demonstrated by integrating both a widely-tunable distributed Bragg reflector (DBR) and distributed feedback (DFB) lasers on the same substrate. By controlling the central gap width and etch depth along the laser mirror length (shown in the figure below) the reflectivities can be tuned and the desired laser characteristics can be achieved without additional lithography cycles. Initially demonstrated on an indium phosphide substrate with DBR and DFB elements, the platform technology shows promise for various other materials and devices like III-V and II-VI semiconductors, silicon-on-insulator (SOI), and planar lightwave circuits (PLCs). With this versatility, the invention described here can streamline PIC production across diverse applications. Proof-of-concept results showcase the lithographic technique’s ability to produce high-performance photonic devices with side-mode suppression ratios over 50 dB (figure on the right) and output powers exceeding 5 mW. These metrics, combined with the lithographic simplicity, highlight the technology’s potential to reduce costs and accelerate PIC manufacturing. Please note that NASA does not manufacture products itself for commercial scale.

The NASA innovation is based on a tessellation algorithm to break up a curved surface into identically sized equilateral surface polygons. Tessellation is a term used in mathematics that describes the process of deconstructing a surface into non-overlapping shapes with no gaps. Using this NASA innovation enables a curved-surface truss structure to be designed and built using all identical module and strut components. A key feature of this innovation is the use of a “multi-nut” connector, which enables curved surface truss structures to be assembled from identical truss modules. Uniform truss modules with customizable multi-nut connectors can be used to construct a curved-surface structure. The algorithm is a design approach for any size or surface shape. The NASA innovation represents a major breakthrough due to: • Versatility to a variety of planar and curved structure shapes (cylinder, sphere, etc.) • Ability to change the shape simply by updating the “multi-nut” connectors • Commonality of truss modules and components • Ease of assembly • Efficiency of construction and weight • Robotic assembly and servicing. In addition to a range of space related applications – mirrors, antennas, habitats, storage containers, etc. – the innovation is also directly applicable to general terrestrial assembly of systems with curvature, including for example sports stadiums, airports, aquariums, convention centers, or bridges.

NASA researchers have developed the PAPA technology to increase the efficiency of the thin-film solar array assembly process, significantly decreasing assembly time and labor costs associated with manufacturing large scale solar arrays. Traditional solar cell assembly is a labor intensive, multi-step, time-consuming process. This manual assembly will not be possible in a space environment. To enable solar array assembly in space, PAPA leverages robotic automation to distill the traditional assembly method into four fully automated steps: applying adhesive to block substrate, placing the solar cells using a vacuum tool attached to a universal robotic arm, printing the interconnects and buses to connect the cells, and applying a protective cover. The PAPA technology is compatible with a variety of thin-film solar cells, including 3D printed cells (essential for future in-space manufacturing of arrays) and terrestrial manufacturing methods. As solar cell technologies mature, PAPA will be able to incorporate advancements into the paneling process. NASA researchers have begun to employ PAPA solar array fabrication and estimate savings of $300-$400/watt. For extraterrestrial assembly of solar panels the size of a football field or larger, PAPA could result in savings of approximately $500 million; a substantial cost savings driven by standardization and efficiency in the solar array assembly process. By demonstrating increases in assembly efficiency, time and cost savings, and passing multiple environmental exposure tests, the PAPA lab protype has completed the final phases of technology development and is ready for scale-up and commercialization.

This NASA Glenn innovation is a novel multi-junction photovoltaic cell constructed using selenium as a bonding material sandwiched between a thin film multi-junction wafer and a silicon substrate wafer, enabling higher efficiencies. A multi-junction photovoltaic cell differs from a single junction cell in that it has multiple sub-cells (p-n junctions) and can convert more of the sun's energy into electricity as the light passes through each layer. To further improve the efficiencies, this cell has three junctions, where the top wafer is made from high solar energy absorbing materials that form a two-junction cell made from the III-V semiconductor family, and the bottom substrate remains as a simple silicon wafer. The selenium interlayer is applied between the top and bottom wafers, then pressure annealed at 221°C (the melting temperature of selenium), then cooled. The selenium interlayer acts as a connective layer between the top cell that absorbs the short-wavelength light and the bottom silicon-based cell that absorbs the longer wavelengths. The three-junction solar cell manufactured using selenium as the transparent interlayer has a higher efficiency, converting more than twice the energy into electricity than traditional cells. To obtain even higher efficiencies of over 40%, both the top and bottom layers can be multi-junction solar cells with the selenium layer sandwiched in between. The resultant high performance multi-junction photovoltaic cell with the selenium interlayer provides more power per unit area while utilizing a low-cost silicon-based substrate. This unprecedented combination of increased efficiency and cost savings has considerable commercial potential. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.