title: Structural evolution and the control of defects in atomic layer deposited HfO2-Al2O3 stacked films on GaAs.
abstract: The structural characteristics and interfacial reactions of bilayered dielectric stacks of 3 nm HfO2/2 nm Al2O3 and 3 nm Al2O3/2 nm HfO2 on GaAs, prepared by atomic layer deposition (ALD), were examined during film growth and the postannealing process. During the postdeposition annealing (PDA) of the Al2O3/HfO2/GaAs structures at 700 °C, large amounts of Ga oxides were generated between the Al2O3 and HfO2 films as the result of interfacial reactions between interdiffused oxygen impurities and out-diffused atomic Ga. However, in the case of the HfO2/Al2O3/GaAs structures, the presence of an Al2O3 buffer layer effectively blocked the out-diffusion of atomic Ga, thus suppressing the formation of Ga oxide. Microstructural analyses showed that HfO2 films that were deposited on Al2O3/GaAs had completely crystallized during the PDA process, even at 700 °C, because of the Al2O3 diffusion barrier. Capacitance-voltage measurements showed a relatively large frequency dispersion of the Al2O3/HfO2/GaAs structure in accumulation capacitance compared to the HfO2/Al2O3/GaAs structure due to a higher interface state density. Conductance results revealed that the Al2O3 buffer layer on GaAs resulted in a significant reduction in gap states in GaAs. The induced gap state in the Al2O3/HfO2/GaAs structure originated from the out-diffusion of atomic Ga into the HfO2 film. Density functional theory calculations supported this conclusion.
authors: Institute of Physics and Applied Physics, Yonsei University, Seoul, 120-749, Korea.
authors: Yu-Seon
authors: YS
authors: Kang
authors: Dae-Kyoung
authors: DK
authors: Kim
authors: Kwang-Sik
authors: KS
authors: Jeong
authors: Mann-Ho
authors: MH
authors: Cho
authors: Chung Yi
authors: CY
authors: Kim
authors: Kwun-Bum
authors: KB
authors: Chung
authors: Hyoungsub
authors: H
authors: Kim
authors: Dong-Chan
authors: DC
authors: Kim