Room-Temperature Mid-, and Far-Infrared Absorption and Electrical Properties of Intercalated GaSe and TlInS2 Crystals

We report room-temperature measurements of the mid- and far-IR absorption throughout the 400 – 4000 cm−1 and 10 – 700 cm−1 spectral ranges and the resistivity of layered p-GaSe and p-TlInS2 intercalated with Li+. Intercalation was performed by immersing Bridgman grown crystals in 0.5 M solutions of LiCl in distilled water at ambient conditions. The crystal structure and the stoichiometry of the grown crystals were determined by X-ray diffraction and XRF methods. It is shown that intercalation does not change the frequency of the IR-, and Raman active low-frequency “rigid layer” mode (GaSe), the space symmetry group or the lattice parameters of the crystals. It was found that for both crystals, the resistivity versus time dependencies are nearly the same. Three ranges in the resistivity-intercalation time dependencies were explained qualitatively. The resistivity increase due to intercalation was explained by assuming that the intercalated lithium ions act as ionized donors and compensate the host p-type crystal. The highest degree of compensation for GaSe and TlInS2 crystals was achieved after intercalation during 12 and 10 days, respectively.