Performance-Improved Vertical Ni/SiO₂/4H-SiC Metal–Oxide–Semiconductor Capacitors for High-Resolution Radiation Detection

Abstract

We report the fabrication of vertical metal–oxide–semiconductor (MOS) detectors with the highest energy resolution ever reported. The MOS detectors have been fabricated on 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick n-type 4H-SiC epitaxial layers by growing a silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer thermally prior to contact deposition. The MOS detectors exhibited leakage currents two orders of magnitude lower than that observed in a Schottky barrier detector (SBD) fabricated on similar 4H-SiC epilayers. The MOS detectors exhibited a much higher energy resolution of 0.4% compared to 0.8% observed in an SBD for 5486-keV alpha particles although both the devices showed a high charge collection efficiency (CCE) of 96% when exposed to the alpha particles. Capacitance mode deep-level transient spectroscopy (C-DLTS) revealed the presence of “lifetime killer” <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{Z}_{\mathrm {1/2}}$ </tex-math></inline-formula> defects in similar concentrations in both the devices, and however, the corresponding capture cross section in the SBD has been observed to be one order of magnitude higher compared to the MOS detector, and instead of EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6/7</sub> center seen in the SBD, the MOS device showed the presence of EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> center. The higher resolution of the MOS device is attributed to the lower leakage current and difference in defect configurations observed between the two devices. The MOS detector showed a positive polarity C-DLTS peak with an activation energy of 1.22 eV, which is likely due to the nonnegligible impedance of the back contact because of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer. The present study opens the great potential of other wide bandgap semiconductor-based vertical MOS detectors, which can be fully depleted for high-resolution X-/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -ray detection.