Leakage current characteristics and the energy band diagram of Al/ZrO2/Si0.3Ge0.7 hetero-MIS structures

Zirconium oxide (ZrO2) films have been deposited on Ge-rich SiGe heterolayers at 150 degrees C by the microwave plasma enhanced chemical vapour deposition (PECVD) technique using zirconium tetra-tert-butoxide. The possible conduction mechanisms in deposited ZrO2 films have been investigated at both room and high temperature. It is found that the conduction mechanism is dominated by Schottky emission at a low electric field (E < 1.2 MV cm(-1)). The intrinsic barrier height between Al and ZrO2 was found to be 0.83 eV. The trap-assisted Poole-Frenkel conduction mechanism is found to take place at a relatively high electric field (E > 1.2 MV cm(-1)). The extracted trap energy is about 0.78 eV from the conduction band of ZrO2. It is shown that the current in ZrO2 films exhibits strong temperature dependence at a low electric field. The trapping behaviour of the charge carriers in thin ZrO2 gate dielectric stacks during constant gate voltage stress of metal-oxide-semiconductor capacitors has also been investigated.