Transport Properties of Cd- and Ni-Doped CuIn(S,Se,Te)₂-Based Semiconductors

Materials based on the chalcopyrite structure can form semiconductors with a wide range of properties. CuInX₂, where X is S, Se, or Te, can be tuned by doping on sites such as the Cu site or the In site to change the amount of carrier concentration. One use for semiconductors such as CuInX₂, with a wide array of doping options, is for thermoelectric applications. Thermoelectric materials are materials with the ability to convert thermal energy such as waste heat into useful electrical energy. By correctly doping CuInX₂, it could allow for a high thermoelectric figure of merit, ZT, to be achieved. In this study, 0, 0.1%, 1%, and 5% Cd or Ni was used to dope on the In site or the Cu site, respectively. All samples showed single phase chalcopyrite structures. CuInS₂ showed n-type behavior throughout the doping range with both Cd and Ni acting as n-type dopants. CuInTe₂ showed p-type behavior throughout the doping range with Cd acting as an electron donor and Ni acting as an electron acceptor. CuInSe₂ showed n-type behavior, which changed to p-type due to both Cd and Ni acting as acceptors. It is possible that higher concentrations of Cd and Ni could still improve the thermoelectric properties of CuInS₂ with a maximum of ZT = 0.1 upon 5% Cd doping and of CuInSe₂ with ZT = 0.27 upon 5% nickel doping. CuInTe₂ was much more efficient with small amounts of Cd improving the ZT from 0.35 to 0.4.