This Phase II Small Business Innovation Research project will deliver an innovative hydrogen passivation technique for improving manufacturability and performance of HgCdTe infrared detectors. Photon-Assisted Hydrogenation (PAH) causes the substrate to be hydrogenated by simultaneous exposure to hydrogen gas and ultra-violet (UV) light which allows hydrogen to diffuse into and become a permanent part of the substrate. In Phase I the feasibility of PAH for the fabrication of high-performance near-infrared HgCdTe avalanche photodiode (APD) arrays on large-area silicon wafers was demonstrated. In Phase II PAH will be optimized for fabrication of HgCdTe infrared sensors from a variety of sources.
The PAH process will not only create a new product line of high-performance HgCdTe/Si-based APDs, but may also provide a means to effect significantly higher yields, and thus lower costs for all manufacturers of HgCdTe-based detectors. PAH technology will enable all HgCdTe infrared device manufacturers to grow on Silicon wafers, significantly reducing the cost of these high value systems, and making them more generally available for a broad range of currently unaffordable applications, including civil transport, aviation, medical and robotic vision systems. Derivatives of the this technique may be applied to the manufacture of a variety of other optoelectronic semiconductor devices requiring passivation to mitigate defects.
Hydrogenation of silicon solar cells and other silicon based electronic devices has been known for years as a way to de-activate defects and enhance performance. In this project we have investigated the usefulness of hydrogenation for improving devices based on compounds composed of mercury cadmium and tellurium. These types of compounds find usefulness, for example, in infrared detectors, imaging systems and solar cells. But they are often prone to defects that occur during growth of the materials and which degrade the performance of the device. Hydrogenation is a promising way to overcome many of the problems that can occur as a result of these defects. Hydrogenation involves activating molecular hydrogen, so that the molecular bond is broken, with the individual hydrogen atoms separating from each other, diffusing into the material, and binding to the defects in the material. The bonding of hydrogen to defects often times deactivates them so that their detrimental effects on device performance are eliminated or reduced. Conventional methods of hydrogenation include hydrogen electric glow discharge, hydrogen cracking on a hot filament, and other means by which the surface is bombarded with hydrogen ions or atoms. But because many of the compounds in this study are much more fragile than silicon, they do not hold up well to the aggressiveness of a glow discharge environment or direct ion bombardment. Instead we have developed a process of photo assisted hydrogenation (PAH), in which ultraviolet light (UV) is used to activate hydrogen and thereby initiate the hydrogenation. This process was found to be much more benign to the material surface than ion bombardment methods, while still being effective at hydrogenation. Another advantage of the photo assisted technique is the ability to achieve selective area hydrogenation by use of a shadow mask that shields regions of a wafer from the UV wherever it is desired to hydrogenate only certain parts of a wafer. This selectivity can be useful, for example, if a wafer contains different kinds of devices, some of which will benefit from hydrogenation while others might be harmed. In this project we used both selective area hydrogenation and broad area hydrogenation in collaboration with several device manufacturers. The results showed very definitive positive results in many, though not all, of the applications investigated. By learning which applications can benefit from hydrogenation, and by developing recipes for the different applications we have begun commercializing the technology.
