Measurements of Neutron Induced Surface and Bulk Defects in 4H Silicon Carbide

摘要

The effects of neutron irradiation was investigated in both n- and p- type 4H silicon carbide. Photoluminescence (PL), deep level transient spectroscopy (DLTS), and Hall effect measurements where used to observe optical and electrical characteristics and identify changes in basic material properties. The material was irradiated using an open pool research reactor. Highly doped n- and p-type materials (ND-NA (caret) 1.2E17 and NA-ND (caret) 1.5E18 cm-3 respectively) were chosen to aid in device fabrication. The material demonstrated no measurable effect to 1 MeV neutrons at fluences of up to 1E14 n/ cm2 and devices were unable to be constructed when exposed to fluences greater then 1E16 n/cm2. The effective suppression of the near bandgap zero phonon PL luminescence lines was shown as a function of increasing neutron fluence, and attributed to the dislocation of neutral nitrogen donors. Deep level defects sites also developed and where shown to increase in density with increased neutron fluence. Hall measurements generally agreed with theoretical expectations but failed to yield conclusive results. Capacitance rollover was observed near 510 K beginning with fluences of around 5E15 n/cm2. Irradiated devices also showed unexpectedly permanent degradation after hour-long exposure to temperatures exceeding 600K during DLTS measurements.