Radiation detection using fully depleted 50 μm thick Ni-4H-SiC epitaxial layer Schottky diodes with ultra-low concentration of Z_(1/2) and EH_(6/7) deep defects

摘要

Recent advances in the development of thick 4H-SiC epitaxial layers for the fabrication of surface barrier radiation detectors have been paving the way for their use in highly penetrating radiation detection. Challenges still exist to achieve full depletion all the way to the epi-layer width, while maintaining a low leakage current at high reverse bias conditions. We report the fabrication of high-resolution and low leakage current Schottky barrier alpha particle detectors with a large active area of 11 mm~2 on 50 μm thick n-type 4H-SiC epitaxial layers, which can be fully depleted. The detectors were cut out of large substrates of 100 mm diameter with a micropipe density ＜1 cm~(-2) in the epi-layers. Mott-Schottky plots obtained from the capacitance-voltage measurements revealed an effective doping concentration of 1.9 × 10~(14)cm~(-3). A parallel plate capacitor model implied that a reverse bias of ～440V was needed to achieve a full-depletion width (50 μm). The current-voltage characteristics demonstrated a very low leakage current of 0.45 nA at a reverse bias of -450 V, which is low enough for the detector to be operated at full-depletion bias. In fact, pulse height spectroscopy using a ~(241)Am alpha source, with the detector biased at -120 V, exhibited a well-resolved alpha spectrum with an energy resolution of 0.8% for the alpha peak corresponding to 5486 keV. This energy resolution was maintained consistently up to a full-depletion bias of -440 V. The ultra-stable performance of the detector has been attributed to the remarkably low concentration of carrier lifetime affecting deep-level defects like Z_(1/2) and EH_(6/7), which were found to be of the order of 10~(12) cm~(-3) or less using capacitance mode deep-level transient spectroscopy measurements.