Temperature variation of photoconductivity in the layered quasi one-dimensional compound TiS3: Semiconducting and unconventional behavior

Abstract

The layered quasi one-dimensional compound TiS3 is remarkable for its optical properties, especially, photoconductivity. Up to now, photoconductivity in TiS3 was studied only at room temperature. Here, we report photoconductivity, δσ, of the TiS3 whiskers in the temperature range of 5–300 K under irradiation in the near-infrared region. With a temperature decrease from room temperature down to T ∼ 100 K, δσ grows moderately, dominated by the variation of the mobility of the electrons. The estimates based on the values of δσ give the recombination time ∼3–25 μs at 300 K. The results show that above ∼100 K, TiS3 behaves as a semiconductor, where electron–hole pairs are excited across the gap, while the recombination goes through transitions of the excited electrons to a donor level with a long lifetime. Below 60 K, a drop of δσ is likely to reveal a phase transition of electrons into a collective state. Another feature in δσ( T) is seen around 17 K, resembling the temperature variation of the conductivity. This feature indicates a drop in the mobility of the electrons. While the behavior of δσ( T) is consistent with the transition of electrons into a collective state, it is strikingly different from δσ( T) of the known quasi one-dimensional conductors with charge-density waves.