Time evolution of surface species during the ALD of high-k oxide on InAs

Understanding the reaction mechanisms involved during the early stage of atomic layer deposition (ALD) of HfO₂ on InAs is a key requirement for improving interfaces in III-V semiconductor-based devices. InAs is an excellent candidate to outperform silicon regarding speed and power consumption, and combined with HfO₂, it gives promise for a new generation of ultra-fast MOSFETs. However, an improved interface quality and in-depth understanding of the involved surface species are needed. Here, we use in situ and operando ambient pressure XPS to follow in real-time the reaction mechanisms which control the ALD chemistry. Besides the removal of all unwanted oxide from the III-V, the same oxygen atoms are found to form HfO_x already from the first half-cycle. In contrast to the standard ALD model, no hydroxyl groups are needed on the InAs surface. Furthermore, we observe an insertion reaction forming unexpected surface species. The second ALD half-cycle allows the immediate removal of all organic species leaving behind a uniform HfO₂ layer partially terminated by hydroxyl groups. We find that prolonged exposure times upon both half-cycles guarantee a sharp InAs/HfO₂ interface. Such an improved interface is an important step towards fast and sustainable III-V semiconductor-based electronics.