Papers by Author: Giuseppe Bertuccio

Abstract: The achievement of nuclear detectors in Silicon Carbide imposes severe constraints on the electronic quality and thickness of the material due to the relatively high value of the energy required to generate an electron-hole pair (7.8 eV) in this material compared to the value for Si (3.6 eV). In this work, 4H-SiC charged particle detectors were realised using epitaxial layers of n-type doping as active region. The thickness of the epilayer is always below 80 μm with a net doping concentration in the range of 8 x 1013 to 1016 cm-3. These properties allowed the fabrication of Schottky diodes that operate well as radiation detectors. At low doping concentration, the epilayer is totally depleted at quite low reverse bias (≈ 50 V), thereby obtaining the maximum active volume.

Abstract: The design and the experimental results of some prototypes of SiC X-ray detectors are presented. The devices have been manufactured on a 2’’ 4H-SiC wafer with 115 m thick undoped high purity epitaxial layer, which constitutes the detection’s active volume. Pad and pixel detectors based on Ni-Schottky junctions have been tested. The residual doping of the epi-layer was found to be extremely low, 3.7 x 1013 cm-3, allowing to achieve the highest detection efficiency and the lower specific capacitance of the detectors. At +22°C and in operating bias condition, the reverse current densities of the detector’s Schottky junctions have been measured to be between J=0.3 pA/cm2 and J=4 pA/cm2; these values are more than two orders of magnitude lower than those of state of the art silicon detectors. With such low leakage currents, the equivalent electronic noise of SiC pixel detectors is as low as 0.5 electrons r.m.s at room temperature, which represents a new state of the art in the scenario of semiconductor radiation detectors.

Abstract: An n-type 8° off-axis <0001> 4H-SiC epitaxial wafer was processed. The n-type epilayer had doping and thickness of, respectively, ~3 × 1015 cm-3 and ~5 μm. p+/n diodes with not terminated junctions were constructed by a selective area implantation process of 9.2 × 1014 cm-2 Al+ ions at 400°C. The diodes had areas in the range 2×10-4 -1×10-3 cm2. The Al depth profile was 6×1019 cm-3 high and 164 nm thick. The post implantation annealing process was done in a high purity Ar ambient at 1600°C for 30 min. The diode current-voltage characteristics were measured in the temperature range 25-290°C. Statistics of 50-100 measurements per device type were done. The fraction of diodes that could be modeled as abrupt junctions within the frame of the Shockley theory decreased with increasing area value, but was always > 75%. The ideality factor was > 2 only at temperatures > 200°C and bias values < 1 V. The leakage current was extremely weak and remained of the order of 10-9 Acm-2 at 70°C and 500 V reverse bias. 4% of the diodes reached the theoretical voltage breakdown that was 1030 V. The surface roughness of un-implanted and implanted regions after diode processing was, respectively, 2 nm and 12 nm.

Abstract: High performance SiC detectors for ionising radiation have been designed, manufactured and tested. Schottky junctions on low-doped epitaxial 4H-SiC with leakage current densities of few pA/cm2 at room temperature has been realised at this purpose. The epitaxial layer has been characterised at different dose of radiations in order to investigate the SiC radiation hardness. The response of the detectors to alpha and beta particle and to soft X-ray have been measured. High energy resolution and full charge collection efficiency have been successfully demonstrated.

Abstract: The damage produced by 2 MeV protons on a 4H-SiC Schottky diode has been investigated by monitoring the charge collection efficiency as the function of the ion fluence. A new algorithm based on the Shockley-Ramo-Gunn theorem has been developed to interpret the experimental results. The fitting procedure provides a parameter which is proportional to the average number of active electrical traps generated by a single ion, which can be profitably used to estimate the radiation hardness of the material.