Processing Diamond Materials for Improved Performance in Quantum Sensing and Power Electronics

Single-crystal diamond grown by chemical vapor deposition (CVD) is a strong candidate material for several emerging applications. The nitrogen-vacancy (NV) center found in diamond has proven to be the most promising platform for room temperature quantum sensing on the nanoscale. This optical technique can measure magnetic field, electric field, strain, and temperature. It takes advantage of a short-lived excited state with a high quantum efficiency of emission. While the physics of NV diamond sensing is established, the reliability and performance of NV diamond has been limited by batch-to-batch inconsistencies and impurities from their preparation. <br/> <br/>The combination of desirable electronic, mechanical, and thermal properties found in diamond also make it optimally suited as a semiconductor material for power electronics and devices operating in extreme environments. It is mechanically robust, chemically inert, non-toxic, with a high thermal conductivity and large carrier mobilities. However, this unique combination of characteristics also engender substantial fabrication difficulties not found in metals and traditional semiconductors. Additionally, the high temperatures and potentials power electronic diamond devices operate at can preclude use of traditional silicon fabrication methods and device components. For this reason, novel materials science processing methods must be developed to fully realize the potential of diamond for these applications.<br/> <br/>Here, we detail our CVD-grown diamond processing efforts to enhance its performance in quantum sensing and power electronics. We constructed a distillation apparatus that allows for treatment of diamond by refluxing perchloric acid without the need for a dedicated perchloric acid fume hood. A thorough spectroscopic investigation including photoluminescence, Raman, X-ray photoemission, energy-dispersive X-ray, and optically detected magnetic resonance spectroscopies to determine the effects of this procedure and subsequent thermal processing steps. As-received general-grade NV diamonds are found to have a layer of graphitic carbon and other impurities present which are largely removed through this processing. This results in an improvement in quantum sensing performance, including substantially longer T₂ and T₂^* times, and allows for the accurate measurement of the ionization energy of the long-lived ¹E singlet state. We also report the development of a processing method for the deposition of alumina on conductive diamond for use as a gate dielectric. We deposited 40-50 nm of Al₂O₃ on H-terminated or B-doped CVD-grown single-crystal diamond using both thermal and a plasma-assisted atomic layer deposition processes, after which it was subjected it to a variety of processing conditions up to 600 °C. Subsequently, metal electrodes were deposited and the electrical breakdown potential of the gate dielectric was determined. Coupled with thorough structural characterization, we revealed the conditions under which diamond devices can be processed and operated without damaging the fidelity of a deposited alumina gate dielectric. Collectively, these advances in diamond processing represent a step towards bringing this material closer to wide commercial applicability in sensing and power electronics.