IDENTIFICATION OF DEEP BANDGAP STATES IN 4H-SIC AND 6H-SIC BY RADIOTRACER DLTS AND PAC-SPECTROSCOPY

Bandgap states of the transition metals Ti, V, and Cr were identified in n-type 4H- and 6H-SiC by radio-tracer Deep Level Transient Spectros copy (DLTS), The radioactive impurities V-46 (decay to Ti-48, T-1/2 = 16.0 d) and Cr-51 (decay to V-51. T-1/2 = 27.7 d) were recoil implante d after (p.n) nuclear reactions. From repeated DLTS measurements revea ling the nuclear decay constants of the elemental transmutations invol ved Ti-, V-, and Cr-related deer levels could be deduced: in 4H-SiC in the upper part of the bandgap two Ti-levels (at 0.13 and 0.17 eV), th ree Cr-levels (at 0.15, 0.18 and 0.74 eV) and one V-level (at 0.97 eV) , which is assigned to the postulated V acceptor state, In 6H-SiC only two V-levels (at 0.71 and 0.75 eV) and one Cr-level (at 0.54 eV) exis t, no deep Ti-level was found. The Perturbed Angular Correlation Spect roscopy (PACS)-studies on the probe atoms In-111, Cd-111, and Hf-181 r eveal electric field gradients (EFG) due to different noncubic lattice sites as well as complex formation with defects and impurities. In he avily N-doped samples a distinct In-111-N-pair is formed, in the case of Cd-111 an analogous Cd-N-pair as well as a complex of one Cd- and t wo N-atoms are observed. (C) 1998 Elsevier Science B.V.