Deep acceptor states of platinum and iridium in4H-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 $\mathrm{Pt}$ and $\mathrm{Ir}$ the radioactive isotope ${}^{188}\mathrm{P}\mathrm{t}$ was incorporated into $4H\mathrm{-SiC}$ samples by recoil implantation. During the nuclear decay of ${}^{188}\mathrm{P}\mathrm{t}$ via the unstable ${}^{188}\mathrm{I}\mathrm{r}$ to the stable ${}^{188}\mathrm{O}\mathrm{s}$, 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 ${}^{188}\mathrm{P}\mathrm{t}$. The two levels are interpreted as one $\mathrm{Pt}$-related defect structure with two different charge states in the band gap of $4H\mathrm{-SiC}$: a double-negative acceptor at $0.81\mathrm{eV}$ and a single-negative acceptor at $1.47\mathrm{eV}$ below the conduction band edge $E_C$. Iridium was found to generate one acceptorlike state $(E_C-0.82\mathrm{eV})$ in the band gap of $4H\mathrm{-SiC}$. Further, acceptor states at $E_C-0.31\mathrm{eV}$, $E_C-0.41\mathrm{eV}$, $E_C-0.50\mathrm{eV}$ and donor states at $E_V+0.60\mathrm{eV}$, $E_V+0.90\mathrm{eV}$, $E_V+1.09\mathrm{eV}$ ($E_V$ 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 $\mathrm{Os}$. Therefore, the assignment to specific $\mathrm{Os}$ 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