Deep acceptor states of platinum and iridium in 4H-silicon carbide

Band gap states of platinum and iridium in the hexagonal polytype 4H of silicon carbide are investigated by means of deep level transient spectroscopy (DLTS) in n- as well as p-type epitaxial layers. To establish a definite chemical assignment of band gap states to Pt and Ir the radioactive isotope ¹⁸⁸Pt was incorporated into 4H-SiC samples by recoil implantation. During the nuclear decay of ¹⁸⁸Pt via the unstable ¹⁸⁸Ir to the stable ¹⁸⁸Os, the concentration of band gap states is traced by DLTS whereby characteristic concentration changes lead to an unambiguous assignment of two band gap states to ¹⁸⁸Pt. The two levels are interpreted as one Pt-related defect structure with two different charge states in the band gap of 4H-SiC: a double-negative acceptor at 0.81 eV and a single-negative acceptor at 1.47 eV below the conduction band edge E_C. Iridium was found to generate one acceptorlike state (E_C−0.82 eV) in the band gap of 4H-SiC. Further, acceptor states at E_C−0.31 eV, E_C−0.41 eV, E_C−0.50 eV and donor states at E_V+0.60 eV, E_V+0.90 eV, E_V+1.09 eV (E_V is the valence band edge) are preliminarily assigned to defects involving osmium. It was found that recoil processes taking place during the nuclear decay may generate different complex structures related to Os. Therefore, the assignment to specific Os structures is not definite. The deep acceptor state of platinum is considered an interesting candidate for a compensating center close to the midgap position in 4H-SiC in order to produce semi-insulating SiC layers and control carrier lifetimes.