Iodine doping of p-type topological insulators*

We report on the systematic iodine (I) doping of the `intrinsically' \textit{p}-type $2^{nd}$ generation topological insulator (TI) Sb$_2$Te$_3$. Iodine will introduce additional holes into the system and thus pull the Fermi level $E_F$ `down' from the Dirac point. Further, at a sufficient hole density, particle correlation effects are also expected to emerge. Iodine was incorporated into Sb$_2$Te$_3$ using two methods: (i) post-growth vapor exposure of crystals grown by the Vapor-Liquid-Solid (VLS) technique and (ii) \textit{in-situ} doping of crystals grown in a modified Bridgman setup. The first method is self-limiting and only up to 2 at\% iodine is entered, however the \textit{in-situ} doping allowed us to increase iodine content up to 20\%. Detailed XRD Rietveld refinement analysis of the doped crystals doping indicates that for the I-content greater than 10\% the rhombohedral structure is modified to reflect some extent of the I-Te and I-Sb bonding. We find that iodine doping affects the large diamagnetic susceptibility, particularly at low magnetic fields. Our measurements of Hall resistivity confirm that under doping resistivity remains \textit{p}-type. The contrasting effects of the iodine doping into the intrinsically \textit{n}-type Bi$_2$Se$_3$ will be presented.