Neutron Reflectometry of Buried Monatomic Hydrogen Layer at the Hetero-Interface in a Highly Mismatched Sr and H-terminated Si(111)

Abstract

Strontium (Sr) is a well-known template on Si for a highly-desirable transistor gate material SrTiO₃. Sr layers are grown epitaxially on hydrogen-terminated Si(111) surface despite the large lattice mismatch of 12%. However, there are still many unclear points concerning the specific interface structure. We need to study how the buried monatomic hydrogen layer behaves to manage the large mismatch. In order to clarify its buried hetero-interface structure related to monatomic hydrogen layer, Si-H bonding states are in situ monitored during Sr growth by Multiple Internal Reflection Fourier Transform Infrared (MIR-FTIR) spectroscopy, and the buried hetero-interface between Sr layer and Si(111) surface is investigated by ex situ neutron reflectometry (NR). FTIR has shown change of Si-H bonding states caused by the Sr growth at the initial monolayer growth stage. Furthermore, we have found the difference in neutron reflectivity profiles between the Sr layers grown on H- and D-terminated Si substrates. These results suggest the existence of buried monatomic hydrogen layer at the hetero-interface acting as an effective component of interface structure to manage the high lattice mismatch.