Abstract:
Silicon Carbide is a wide bandgap semiconductor with excellent physical and opto-electrical properties. Among these excellent properties are its radiation hardness, high temperature operation and high electric field breakdown. SiC can therefore be used in the fabrication of electronic devices capable of operating in harsh environments, e.g. radiation detectors. Like any other semiconductor, the success of SiC in device fabrication depends on elimination of defects that are detrimental to desired devices or controlled introduction of desired energy levels. The first step in so doing is understanding the defects that are either found in as grown material, introduced during device fabrication or introduced during device operation.
In this study nickel ohmic and Schottky contacts were resistively fabricated on n-type 4H-SiC with a net doping density of 4 × 1014 cm-3. Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and Laplace-DLTS measurement techniques were used to electrically characterize the fabricated Schottky diodes. The diodes were then irradiated with low energy electrons, alpha particles and protons. The characterization measurements were repeated after irradiation to evaluate the effect of irradiation on the electrical properties of SiC.
It was observed from I-V measurements that electron, alpha particle and proton irradiations do not significantly affect the rectification of Ni/SiC Schottky contacts. C-V measurements indicated that the free carrier removal rate is higher for alpha particle irradiation as compared to electron irradiation. The irradiated diodes were annealed in argon ambient and significant recovery in the free carrier concentration was observed below 600 °C. The free carrier concentration of proton irradiated Schottky contacts, which was decreased to below detection levels was also partly recovered after heat treatment of up to 400 °C. DLTS and Laplace-DLTS measurements revealed the presence of four defect levels in as-grown 4H-SiC. These defects have been labelled E0.10, E0.12, E0.17 and E0.69 where the subscripts indicate the activation energies of the respective defects. Electron, alpha particle and proton irradiations were observed to induce three more defect levels with activation energies of 0.42 eV, 0.62 eV and 0.76 eV. Additionally, these irradiations were also observed to enhance the concentration of level E0.69. All the radiation induced defects were annealed out at temperatures below 600 °C. In proton irradiated diodes, another defect with activation energy of 0.31 eV was observed after annealing the irradiated diodes at 625 °C.
