1T-TiSe2-δ: a Se-vacancy induced p-type semiconductor
黃松勳1,2*, 殳國俊1, 白偉武1, 劉祥麟2, 周方正1,3,4
1Center for Condensed Matter Science, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Taiwan Normal University, Taipei, Taiwan
3National Synchrotron Radi Radiation Research Centeration Research Center, Hsinchu, Taiwan
4Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan
* presenting author:Song-Hsun Huang, email:syuyahui@gmail.com
The normal state properties (semimetal vs. semiconductor) of 1T-TiSe2 have been the subject of debate. We performed the systematic study with controlled Se vacancy levels, indicating this controversy could be due to the neglected factor of severe Se loss during the crystal growth. The charge density wave (CDW) state emerging below ~200 K was most pronounced in samples of δ ~ 0.12, corresponding to one to two Se atoms missing per closely packed seven-TiSe6 octahedral unit in hexagonal shape, and leading to the earlier proposed 2 × 2 × 2 CDW in 3D. Furthermore, the anomalous resistivity ρ(T) peak between 100-200 K showed the onset of a CDW phase near ~200 K with a carrier type changing from p- to n-type. An interpretation based on a semiconductor with a p-type doped impurity band and a molecular orbital model was proposed to explain the evolution of Se vacancy level and temperature dependence of electronic structural changes for 1T-TiSe2, from the low doping semiconducting behavior to the heavily doped dirty semiconductor showing n-type conduction similar to a metal. Supporting evidences for the existence of Se vacancy have been provided by the integrated chemical and physical property analyses including electron microprobe analysis (EPMA), scanning tunneling microscopy (STM), resistivity, Hall coefficient, and magnetic susceptibility.

Keywords: TiSe2, CDW