Hee Jae Kang

Bio: Hee Jae Kang is an academic researcher from Chungbuk National University. The author has contributed to research in topics: Thin film & Band gap. The author has an hindex of 19, co-authored 86 publications receiving 993 citations.

Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

Abstract: The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS) HR-REELS with a primary electron energy of 03 keV revealed that the surface F center (FS) energy was located at approximately 42 eV above the valence band maximum (VBM) and the surface band gap width (EgS) was approximately 63 eV The bulk F center (FB) energy was located approximately 49 eV above the VBM and the bulk band gap width was about 78 eV, when measured by REELS with 3 keV primary electrons From a first-principles calculation, we confirmed that the 42 eV and 49 eV peaks were FS and FB, induced by oxygen vacancies We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies Finally, we calculated the secondary electron emission yields (γ) for various noble gases He and Ne were not influenced by the defect states owing to their higher ionization energies, but

Band gap and band offsets for ultrathin (HfO2)x(SiO2)1−x dielectric films on Si (100)

Abstract: Energy band profile of ultrathin Hf silicate dielectrics, grown by atomic layer deposition, was studied by using x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap energy only slightly increases from 5.52eV for (HfO2)0.75(SiO2)0.25 to 6.10eV for (HfO2)0.25(SiO2)0.75, which is much smaller than 8.90eV for SiO2. For ultrathin Hf silicate dielectrics, the band gap is mainly determined by the Hf 5d conduction band state and the O 2p valence band state. The corresponding conduction band offsets are in the vicinity of 1eV, which satisfies the minimum requirement for the carrier barrier heights.

Electronic and optical properties of Al2O3/SiO2 thin films grown on Si substrate

Abstract: The electronic and optical properties of Al2O3/SiO2 dielectric thin films grown on Si(1 0 0) by the atomic layer deposition method were studied by means of x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS) The band gaps of the Al2O3/SiO2 thin films before annealing and after annealing were 65 eV and 75 eV, respectively, and those of the γ-Al2O3 and α-Al2O3 phases were 71 eV and 84 eV, respectively All of these were estimated from the onset values of the REELS spectra The dielectric functions were determined by comparing the effective cross-section determined from experimental REELS with a rigorous model calculation based on dielectric response theory, using available software packages The determined energy loss function obtained from the Al2O3/SiO2 thin films before annealing showed a broad peak at 227 eV, which moved to the γ-Al2O3 position at 243 eV after annealing The optical properties were determined from the dielectric function The optical properties of the Al2O3/SiO2 thin films after annealing were in good agreement with those of γ-Al2O3 The changes in band gap, electronic and optical properties of the Al2O3/SiO2 thin films after annealing indicated a phase transition from an amorphous phase to the γ-Al2O3 phase after annealing

Band alignment of atomic layer deposited (ZrO2)x(SiO2)1−x gate dielectrics on Si (100)

Abstract: The band alignment of atomic layer deposited (HfZrO4)1−x(SiO2)x (x = 0, 0.10, 0.15, and 0.20) gate dielectric thin films grown on Si (100) was obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence band offset, and conduction band offset values for HfZrO4 silicate increased from 5.4 eV to 5.8 eV, from 2.5 eV to 2.75 eV, and from 1.78 eV to 1.93 eV, respectively, as the mole fraction (x) of SiO2 increased from 0.1 to 0.2. This increase in the conduction band and valence band offsets, as a function of increasing SiO2 mole fraction, decreased the gate leakage current density. As a result, HfZrO4 silicate thin films were found to be better for advanced gate stack applications because they had adequate band gaps to ensure sufficient conduction band offsets and valence band offsets to Si.

Reflection electron energy loss spectroscopy for ultrathin gate oxide materials

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Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells

Abstract: The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Abstract: Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Electronic and optical properties of Cu, CuO and Cu2O studied by electron spectroscopy

Abstract: The electronic and optical properties of Cu, CuO and Cu(2)O were studied by x-ray photoelectron spectroscopy (XPS) and reflection electron energy-loss spectroscopy (REELS). We report detailed Cu 2p, Cu LVV, O 1s and O KLL spectra which are in good agreement with previous results. REELS spectra, recorded for primary energies in the range from 150 to 2000 eV, were corrected for multiple inelastically scattered electrons to determine the effective inelastic scattering cross section. The dielectric functions and optical properties were determined by comparing the experimental inelastic electron scattering cross section with a simulated cross section calculated within the semi-classical dielectric response model in which the only input is Im(-1/e) by using the QUEELS-e(k,ω)-REELS software package. By Kramers-Kronig transformation of the determined Im(-1/e), the real and imaginary parts (e(1) and e(2)) of the dielectric function, and the refractive index n and extinction coefficient k were determined for Cu, CuO, and Cu(2)O in the 0-100 eV energy range. Observed differences between Cu, CuO and Cu(2)O are mainly due to modifications of the 3d and O 2p electron configurations.

Scaling the gate dielectric: materials, integration, and reliability

Abstract: In this paper a review of the more "fundamental" concerns regarding the scaling of the gate dielectric in the ultrathin regime is presented. Material issues are discussed pertaining to the integration of silicon oxynitride and oxide/nitride stacked layers and how such films might reduce or minimize boron penetration problems and address leakage current and reliability concerns. A methodology is presented to calculate device and chip lifetimes for MOS structures on the basis of data extracted from voltage- and temperature-accelerated measurements. Some integration issues regarding higher-k materials are also discussed because of their ability to solve the scaling problem. However, difficulties are involved in integrating them into a CMOS process flow.