Growth and Characterization of Germanium-based type I Clathrate Thin Films Deposited by Pulsed Laser Ablation

Thin films of clathrate material have been grown using the laser ablation technique on a variety of substrates. Films deposited on silicon substrates exhibited a significant deficiency of Ga and Ge while the stoichiometry was preserved in films deposited on quartz, sapphire, and glass substrates. Ablation characteristics of the clathrate target for laser radiation at three different wavelengths in the UV, visible and IR were studied. The UV and IR laser wavelengths produce low ablation thresholds and high growth rates. Crystalline films were obtained above a growth temperature of 400C. Conductivity measurements on the films at low current injection (<40 μA) showed semiconducting behavior. At high currents the films demonstrated a semiconductor-to-metal transition for temperatures lower than 150 K.