Reduced PIC fabrication cost by one-step method

Serial Arrayed Waveguide Grating enables higher resolution wavelength separation. Traditional AWGs split the optical signal into multiple parallel paths each with a different path length. This new approach creates the different path lengths by splitting the signal into essentially one long path in which the different channels are periodically split off the main path in the desired fraction. This has the net result of requiring much less space on-chip for comparable optical path differences. In traditional AWG, there are multiple parallel optical paths, each with a different engineered path-length. For high resolution, you want many different parallel paths and large differences in path length between the paths. To design this on a photonics chip requires significant area. The serial AWG creates a single path, equivalent to the longest path in the parallel AWG and split off fractions of the optical signal at various points along the way to create the equivalent path lengths. Serial Arrayed Waveguide Grating re-uses the same path instead of needing independent parallel paths.

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.

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.

This innovation represents an alternative method to skip several of the conventional fabrication steps, using a mask designed to allow molecules in a sputtering plume to pass through openings engineered in the mask. This causes material to go where desired, without photoresist, and without selective etching, thus simplifying the process, reducing cost, chemical waste; and increasing throughput. This method masks areas that do not need deposited material, causing local deposition instead. The shape and size are within tolerance. No etching steps, no photoresist patterning, and no metal removal is necessary. Other than planarization, selective deposition has replaced every step in the conventional process, accomplishing the same result in 8 steps instead of 19. The technology can be easily used to fabricate custom chips and specialized sensors and devices that use the group III-V and II - VI semiconductor materials.

This technology is an integrated hybrid crystal LED display device that can emit red, green, and blue colors on one single wafer. Todays LEDs are built with many compound semiconductors with type-I direct bandgap energies of two different crystal structures. While Red, Orange, Yellow, Yellowish Green LEDs are commonly made with III-V semiconductor alloys of Aluminum Gallium Indium Phosphide (AlGaInP) and Aluminum Gallium Indium Arsenide (AlGaInAs) with cubic zinc blende crystal structures, the higher energy colors such as green, blue, purple, and Ultra-Violet(UV) LEDs are made with III-Nitride compound semiconductor of AlGaInN alloys with hexagonal wurtzite crystal structures. Because the atomic crystal structures are different for red LED and green/blue LEDs, the integration of these semiconductor LEDs as individual R, G, B pixels on one wafer was almost impossible or very difficult so far.