Deep acceptor states of platinum and iridium in4H-silicon carbide

Abstract

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 $0.81\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and a single-negative acceptor at $1.47\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below the conduction band edge ${E}_{C}$. Iridium was found to generate one acceptorlike state $({E}_{C}\ensuremath{-}0.82\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ in the band gap of $4H\mathrm{-SiC}$. Further, acceptor states at ${E}_{C}\ensuremath{-}0.31\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, ${E}_{C}\ensuremath{-}0.41\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, ${E}_{C}\ensuremath{-}0.50\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and donor states at ${E}_{V}+0.60\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, ${E}_{V}+0.90\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, ${E}_{V}+1.09\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (${E}_{V}$ 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 $4H\text{\ensuremath{-}}\mathrm{SiC}$ in order to produce semi-insulating $\mathrm{SiC}$ layers and control carrier lifetimes.