Change in crystalline structure and band alignment in atomic-layer- deposited HfO₂ on InP using an annealing treatment

Changes in structural characteristics and band alignments of atomic-layer-deposited HfO₂ films on InP (001) as a function of annealing temperature and film thickness were investigated using various analytical techniques. After an annealing at temperatures over 500°C, the HfO₂ films were converted into a fully crystalline structure with a tetragonal phase with no detectable interfacial layer between the film and the InP substrate. In-P-O states, produced by interfacial reactions, were increased during the post deposition annealing (PDA) process and oxides were detected in the surface region of the HfO₂ film, indicating that In and P atoms had out-diffused. The E_g value of the as-grown HfO₂ film was found to be 5.80 ± 0.1 eV. After the PDA treatment, the optical band gap and valence band offset values were significantly affected by the interfacial oxide states between the HfO₂ film and InP substrate. Moreover, band bending in InP, due to negative space charges generated by an unstable P-rich interfacial state during atomic layer deposition process was decreased after the annealing treatment.