Low Doped SiC Epiwafers for Room Temperature, Ultrafast, and Radiation Hard Sensors

Silicon-based sensors are widely used in high energy and heavy ion collider experiments but suffer from high susceptibility to bulk radiation damage. To extend lifetime and reliability, Si-based detectors must be cooled to very low temperatures to increase its radiation hardness requiring bulky and complex cooling systems. The robust electronic, thermal, and radiation hardness properties of SiC makes the prospect of SiC-based detectors an appealing alternative. Where Si detectors commonly operate below 0 °C, the wide bandgap energy, low intrinsic carrier concentration, and high thermal conductivity of SiC allow devices to theoretically operate at temperatures upwards of 300 °C without cooling requirements. Furthermore, the intrinsically high atomic displacement energy of SiC provides resistance to radiation damage caused by neutrons and heavy charged particles responsible for the generation of charge trapping and generation centers. However, SiC processing technology has more complex requirements than that of Si such as high growth and processing temperatures, stoichiometry control, managing polytype competition, and expensive substrate manufacturing processes. Consequently, SiC processing still requires advancement to fully realize the benefits of its robust materials properties for certain applications of radiation detection. For high energy physics in particular, detectors of low ionizing energy particles require thick active regions to ensure the number of excitons generated is significantly higher than the equivalent noise charge generated by the detector read-out circuit system. Furthermore, detector active regions require high purity, low defect, and homogenous single crystals to achieve full charge collection, low leakage current, and good energy resolution. The combination of these requirements poses the greatest challenge for SiC epitaxial growth processes as it relates to end-use performance of high energy physics detectors. Mainstream Engineering will develop an ultrahigh purity epitaxy process based on our proven high growth rate, low-defect halide-CVD epitaxy process of thick 4H-SiC n- drift layers for ultrahigh voltage power electronics devices. Modifications to our standard growth process will include the use of ultrahigh purity (UHP) precursors and in situ purification of carrier gases, implementation of pre-growth reactor conditioning such as in situ halogen purification and high temperature baking, and tuning epitaxy process parameters such as C/Si ratio, temperature, and pressure. We will also demonstrate a post-epi charge carrier lifetime enhancement process. By instituting these supplemental strategies, we will target growth of epilayers to thicknesses of 50-75 µm at growth rates = 100 µm/hr with intrinsic doping concentrations = 5x1013 cm-3 and carrier lifetimes of ~ 10 µs. Electronic grade SiC represents an important technological enabler across several research, commercial, and industrial sectors including green energy, automotive, HV energy transport/smart-grid, and extreme environment sensors applications. The technology developed as a result of this program will contribute to enabling higher performance, faster, lighter, smaller, more efficient and lower cost power electronics systems for commercial users.