Crystallization of HfO₂ in InAs/HfO₂ core–shell nanowires

We report the impact of deposition parameters on the structure of HfO₂ covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO₂ deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO₂ regions was investigated by high-resolution transmission electron microscopy (TEM) and x-ray diffraction. Compared to the deposition on planar Si substrates, the formation probability of crystalline HfO₂ on InAs NWs is significantly enhanced. Here, even 3 nm thick films deposited at 250 °C are partly crystalline. Similarly, a low deposition temperature of 125 °C does not result in completely amorphous 10 nm thick HfO₂ films, they contain monoclinic as well as orthorhombic HfO₂ nanocrystals. Combining HfO₂ and Al₂O₃ into a laminate structure is capable of suppressing the formation of crystalline HfO₂ grains. (paper)