HCDS is a precursor for a variety of industrial applications, including electronics and semiconductors, aerospace industry, solar cells, and fiber optics, however manufacturing of high purity HCDS is still a challenge that require extensive HCDS technology expertise and chemistry know-how. Altogen Chemicals, a Texas-based manufacturer of HCDS provides high purity HCDS for specific industry applications. There are three purity grades which develop during the processes leading up to the manufacture of polysilicon: low, high, and ultrahigh. Low purity is high in metallic contamination and tends to degrade and decrease efficiency and reliability. High and ultrahigh pure HCDS, on the other hand, have been refined to the point metallic impurities measure approximately 1 ppb. Thin films for solar and microchip applications, as well as base glass for fiber optics, require high to ultrahigh purity. The capture and distilling of HCDS is extremely beneficial to silicon based industries due to the ability to refine the chemical to the ultrahigh purity necessary for semiconductors and microelectronics.
Amorphous thin film solar cells (a-Si) are produced via the Siemens process, and layering is performed via plasma enhanced chemical vapor deposition method (PECVD). As in standard CVD, HCDS is employed in PECVD to enhance electrical conductivity and mitigate oxidation. The advantages of a-Si are that unlike a rigid crystalline cell, a-Si cells can be fabricated for a variety of flexible applications such as fabric integration in backpacks, shade cloth, and rollouts on rooftops that cannot support weight of traditional panels. Purity levels in the substrate also affect the efficiency of a-Si cells. The MG and EG are factors to be considered. EG a-Si is produced by hydrogenation (a-Si:H), a method that introduces hydrogen into the HCDS reaction gas phase of PECVD into a stacked layer of silicon. This process allows the cell to absorb up to 90% of sunlight hitting it as these layers become excited by the influx of photons flowing through them. The current drawback to a-Si is that the cells tend to degrade at a faster rate than crystalline cells in high temperature environments, thereby reducing their overall efficiencies. Research into hydrogen diluted silane gas and ways to trap light in active optic layers is ongoing to resolve this issue.
Silicon has proven to be the ideal substrate as the basis for fiber optic production. Just as photons need to be manipulated in stacked a-Si:H to enhance efficiency, they also need to be manipulated in stacked fiber optics to increase electrical conductivity. The PECVD method is employed in the production of fiber optics due to the ability to control uniformity of the deposition and allow for layering of the substrate. Reaction and carrier gases are required and HCDS has been utilized as a precursor in this process. HCDS promotes crystalline growth on a substrate, a necessary step in fiber optic fabrication to form the nanotubes required to transport electrons through the layers.
Another form of deposition that has been utilized is atomic layer deposition (ALD). This process allows for controlling the thickness of the film at sub-nanometer levels. Although this process results in enhancements of electrical transport through the layers, the high temperature requirement for deposition is very limiting. Research in this area is ongoing and shows great promise for the future.
There is much interest in alternative energy production and storage solutions in response to global economic, environmental, and geopolitical concerns. Fuel cells hold the promise of delivering on both, making them economical and convenient to produce and use energy. Fuel cells are comprised of cathodes, anodes, and an electrolyte which generate electric energy through a chemical reaction involving hydrogen and oxygen (and possibly other chemicals depending on the type of membrane used). The byproduct is water. There are three types of polymer electrolyte membranes (PEMs): proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMCFs), and alkaline membrane fuel cells (AMFCs). PEMFCs seem to be getting the most attention, and with good reason as the research shows PEMFCs perform better under higher temperatures, pressure, and humidity than the other cells.
Micromachining of fuel cells based on a silicon substrate and incorporating thin film deposition has been undertaken. Because fuel cell technologies are still in their infancy and mainly at the research stages, the field results are yet to be seen. However, because of the ability of silicon to enhance electrical selectivity, withstand high temperatures, and are stable, the promise is there that this will be a cost effective, safe alternative to toxic chemicals utilized in other PEMs. With regard to HCDS application, after thoroughly reviewing the available literature, it is unclear whether HCDS is incorporated into this production system. However, based on the chemical’s successes in other micromachining fabrications utilizing a silicon substrate and deposition, it would be a viable choice and research into its use in this application is thus recommended.