Effects of nitrogen incorporation in HfO₂ grown on InP by atomic layer deposition: An evolution in structural, chemical, and electrical characteristics

We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO₂ thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH₃ vapor (PDN) at 600 °C, an InN layer formed at the HfO₂/InP interface, and ionized NH_x was incorporated in the HfO₂ film. We demonstrate that structural changes resulting from nitridation of HfO₂/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO₂/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO₂/InP interfaces). Consequently, the tetragonal structure of HfO₂ transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO₂ and InP. During postdeposition annealing (PDA) in HfO₂/InP at 600 °C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO₂/InP structures at 600 °C, nitrogen incorporation in the HfO₂ film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (D_it) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO₂/InP increased the electron-barrier height to ∼0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V.