Defect States in ALD-HfO2 Films on InP Compound Semiconductor as a Function of Film Thickness

We investigated the chemical states and nature of the defect states below the conduction band edge of atomic-layer-deposition HfO₂ grown on InP substrates as a function of film thickness.  Changes in electronic structure of HfO₂ film on InP (001) as a function of film thickness were investigated using high resolution x-ray photoelectron spectroscopy (HR-XPS) and x-ray absorption spectroscopy (XAS). OK₁-edge absroption spectra of the HfO₂/InP showed the conduction band edge states in HfO₂ were increased when the film thickness was increased. DFT calculations and conductance results indicated that these conduction band defect states were caused by the oxygen point vacancy in HfO₂ related with Hf³⁺ states. Moreover, we found the mid-gap states within the InP band gap were caused by out-diffused InP substrate elements into the HfO₂ film. By the combination analysis of XAS, XPS, DFT, and conductance, we conclude that (i) the conduction band edge defect states were resulted from the oxygen point vacancy into the HfO₂ film, (ii) the mid-gap states within the InP band gap were resulted from the out-diffused P elements into HfO₂ film near the HfO₂/InP interface.