Date of Award
Open Access Dissertation
Krishna C. Manda
Epitaxial 4H-silicon carbide (4H-SiC) is an essential semiconductor material for the development of harsh environment radiation detectors due to its excellent electrical and thermal properties and resistance to radiation damage, opening the door for a wide variety of applications in NASA space missions, nuclear safeguards, and nuclear energy. However, the low atomic numbers of its constituent atoms Si (Z = 14) and C (Z = 6) make 4H-SiC nearly transparent to most neutrally charged radiation which can only be compensated using thicker active volumes.
In this dissertation, Ni/n-4H-SiC Schottky barrier diode (SBD) radiation detectors are fabricated for the first time on 250 µm thick 4H-SiC epitaxial layers—the thickest epilayers used for radiation detection to date. The detectors were found to have low leakage current densities-800 V and benchmark 5486 keV alpha particle energy resolutions of1/2.
Further studies were conducted to characterize the effects of harsh environment conditions on the properties of the detectors. First, temperature variation of the leakage current at elevated temperature was studied by temperature-dependent current voltage (IV-T) measurements on 150 µm epitaxial layers which revealed that traps such as Z1/2 and EH6/7 and low barrier patches in spatial geometry of the metal-semiconductor (M-S) interface can produce excess leakage current compared to thermionic emission-diffusion (TED) theory. Next, the effect of neutron irradiation up to fluences of 1013 cm-2 was studied using 250 µm epilayers. Detector energy resolution was shown to degrade with increasing fluences which was correlated with the formation of three new deep levels at 0.8, 1.2, and 1.8 eV below the conduction band. These levels were found to correspond to—based on density functional theory calculations with hybrid pseudopotentials—silicon displacement-related defects formed from the collision of fast neutrons (> 1 MeV) with the silicon nucleus.
Kleppinger, J. W.(2022). Epitaxial 4H-SiC Radiation Detectors for Harsh Environment Applications. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6735