Description: Silicon Carbide deep UV detectors can achieve large gains, high signal-to-noise ratios and solar-blind operation, with added benefits of smaller sizes, lower operating voltages, radiation hardness, ruggedness and scalability. SiC UV APDs implementation is challenging due to some material defects, relatively not-well modeled device operation, and very high absorption coefficients near 200nm wavelengths. The objective of this proposed work is to extend the state-of-the-art in UV sensors by: a) developing SiC deep UV detectors, and b) improving their responsivity down to near 200nm wavelengths. We plan to accomplish this goal by using the SiC UV APD design simulator developed in Phase I, and making further improvements as we introduce new design concepts to improve the responsivity utilizing novel design and fabrication techniques tof the critical n+ top contact layer on the APD to reduce charge recombination in the UV absorption layer. We will develop unique fabrication techniques to improve surface quality of the SiC APD structure. This effort will be led by Auburn University, which has developed state-of-the-art fabrication methodologies and capabilities for SiC MOSFETs, in collaboration with CoolCAD who will design the devices and the implantation process. Our main effort will focus on generating a built-in surface field by creating a steep doping profile right at the surface. Since steep dopant gradients necessary to create a field within 40nm of the surface are not feasible using epitaxial growth techniques for SiC, we will develop implantation and dopant activation sequences, and backend processing techniques to achieve this goal. By creating a field in the deep UV absorption layer (~40nm), we will reduce the initial recombination of electron-hole pairs created by the UV photons and increase current reaching the multiplication region of the APD.

Benefits: Characteristics such as visible-blind operation and potentially 1E15 factor lower dark current than Silicon make SiC based detectors especially attractive for the many UV and EUV needs expressed in NASA's future missions. These programs include the Global Atmospheric Composition Mission (GACM) for monitoring atmospheric ozone and related gasses as well as the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission for monitoring aerosols, ozone, air pollution and coastal ecosystems. In addition, the Geostationary Operational Environmental Satellite (GOES-S) will require instruments to monitor UV from solar flares and the Sun's atmosphere, as well as the Sun's extreme UV radiation. According to the Heliophysics Roadmap of 2009, EUV Avalanche Photo detectors will be necessary for imaging very low intensity UV radiation in order to amplify extremely low photon flux UV signals. The low dark current of wide band-gap SiC APDs will help to realize low flux UV detectors, where detecting flux rates as low as six photons per second are being sought. SiC APD's will operate at relatively low voltages compared to PMTs. By utilizing solid state technology, wide bandgap based UV spectrometers will offer a lightweight and small volume instrument option for use in space vehicles. In summary, SiC APDs will provide benefits to NASA for many years by expanding its imaging capabilities into the EUV regime with higher resolutions and enhanced signal-to-noise ratios.

Non-NASA commercial applications include UV spectrometry for the military, the semiconductor industry, as well as the food processing and healthcare industries where bacterial sterilization, identification, and classification, are important. A particular unique application that can take further advantage of the wide bandgap of SiC detectors, in addition to solar-blindness and low noise qualities, is their applicability to high temperature operation. High temperature applications can include monitoring of UV in rocket plumes and jet engines. Fires in jet engines are of safety concern to the U.S. Air Force and commercial airplane manufacturers. We plan to develop relationships with firms that develop and market sensors, such as Integrated Micro Sensors of Houston, Texas, in an effort to partner with them to license or market high temperature UV sensors that are a unique outcome of this R&D effort. Deep UV detectors are also one of the enabling technologies for UV Non-Line-of-Sight (NLoS) communication networks that have the added benefit of data security.