Structural evolution and the control of defects in atomic layer deposited HfO2-Al2O3 stacked films on GaAs

Yu Seon Kang, Dae Kyoung Kim, Kwang Sik Jeong, Mann Ho Cho, Chung Yi Kim, Kwun Bum Chung, Hyoungsub Kim, Dong Chan Kim

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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 Al2O 3/HfO2/GaAs structures at 700 C, large amounts of Ga oxides were generated between the Al2O3 and HfO 2 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 Al 2O3/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/Al2O 3/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.

Original languageEnglish
Pages (from-to)1982-1989
Number of pages8
JournalACS Applied Materials and Interfaces
Volume5
Issue number6
DOIs
Publication statusPublished - 2013 Mar 27

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All Science Journal Classification (ASJC) codes

  • Materials Science(all)

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