Changes in the structure of an atomic-layer-deposited HfO2 film on a GaAs (100) substrate as a function of postannealing temperature

Abstract

The effects of postannealing temperature on the crystal structure and energy band gap (Eg) values of atomic-layer-deposited HfO2 films grown on a GaAs (100) substrate were investigated. In postannealed HfO2 films prepared using a rapid thermal annealing (RTA) process in a N2 ambient at temperatures over 600 °C, the initially produced, partially crystallized HfO2 film changed into a well-ordered crystalline structure with no detectable interfacial layer between the film and the GaAs substrate. In the case of a RTA prepared at 700 °C, the thickness of the film was relatively increased compared to that of an as-grown film. Changes in the depth profile data related to stoichiometry and electronic structure after the annealing treatment indicated that Ga oxide is formed within the HfO2 film during the RTA. The formation of Ga oxide in the film significantly affected the Eg values, i.e., the Eg changed from 5.5 for an as-grown film to 4.7 eV for a film annealed at 700 °C.