@article{min_yoo_sohn_ko_cho_chung_lee_2010, title={Behavior of strain at a thin Ge pile-up layer formed by dry oxidation of a Si0.7Ge0.3 film}, volume={518}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2009.07.145}, abstractNote={The change of strain in Si0.7Ge0.3 films was investigated with medium energy ion scattering (MEIS). Si was removed in the films by selective oxidation at 800 °C, resulting in the formation of a Ge pile-up layer on the surface. The relaxation and the thickness of the pile-up layer were closely related to the oxidation time. MEIS data demonstrated that relaxation of the Ge layer in the depth direction occurred partially, and that the rates of relaxation decreased with depth. In addition, the rate of relaxation increased with the oxidation time. Lastly, the relaxation of the Ge layer affected the strain of the remaining Si0.7Ge0.3 substrate.}, number={8}, journal={THIN SOLID FILMS}, author={Min, B. -G. and Yoo, J. -H. and Sohn, H-C. and Ko, D. -H. and Cho, M. -H. and Chung, K-B and Lee, T. -W.}, year={2010}, month={Feb}, pages={2065–2069} }
 @article{gundogdu_lucovsky_chung_kim_nordlund_2009, title={Application of non-linear optical second harmonic generation and X-ray absorption and spectroscopies to defect related properties of Hf silicate and Hf Si oxynitride gate dielectrics}, volume={86}, ISSN={["1873-5568"]}, DOI={10.1016/j.mee.2009.03.004}, abstractNote={Three different Hf oxide based dielectrics have emerged as viable candidates for applications in advanced ULSI devices. This article focuses on two of these: (i) phase separated Hf silicates with (i) 70-85% nano-crystalline HfO2 with a nano-grain size <2nm, and 15-30% ~2nm non-crystalline SiO2 inclusions, and (ii) Hf Si oxynitride alloys, the most promising of which has a composition, (HfO2)0.3(SiO2)0.3(Si3N4)0.4 designated as 3/3/4 Hf SiON. X-ray absorption spectroscopy has been applied to identification of defect associated with vacancy structures in phase separated silicates, and network disruption defects in the Hf Si oxynitrides. Optical second harmonic generation is introduced in this article for the first time as a non-invasive approach for detecting macroscopic strain, that is shown to be absent in these low defect density dielectrics, the phase separated Hf silicates, and Hf Si oxynitrides, but present in HfO2 films, and Hf silicates with lower HfO2 content, e.g., the 40% HfO2 film of this article.}, number={7-9}, journal={MICROELECTRONIC ENGINEERING}, author={Gundogdu, K. and Lucovsky, G. and Chung, K-B. and Kim, J. -W. and Nordlund, D.}, year={2009}, pages={1654–1657} }
 @article{kim_cho_cho_chung_suh_ko_an_kim_lee_2009, title={Changes in the structure of an atomic-layer-deposited HfO2 film on a GaAs (100) substrate as a function of postannealing temperature}, volume={95}, ISSN={["0003-6951"]}, DOI={10.1063/1.3182702}, abstractNote={The effects of postannealing temperature on the crystal structure and energy band gap (Eg) values of atomic-layer-deposited HfO2 films grown on a GaAs (100) substrate were investigated. In postannealed HfO2 films prepared using a rapid thermal annealing (RTA) process in a N2 ambient at temperatures over 600 °C, the initially produced, partially crystallized HfO2 film changed into a well-ordered crystalline structure with no detectable interfacial layer between the film and the GaAs substrate. In the case of a RTA prepared at 700 °C, the thickness of the film was relatively increased compared to that of an as-grown film. Changes in the depth profile data related to stoichiometry and electronic structure after the annealing treatment indicated that Ga oxide is formed within the HfO2 film during the RTA. The formation of Ga oxide in the film significantly affected the Eg values, i.e., the Eg changed from 5.5 for an as-grown film to 4.7 eV for a film annealed at 700 °C.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Kim, C. Y. and Cho, S. W. and Cho, M. -H. and Chung, K. B. and Suh, D. C. and Ko, D. -H. and An, C. -H. and Kim, H. and Lee, H. J.}, year={2009}, month={Jul} }
 @article{seo_bellenger_chung_houssa_meuris_heyns_lucovsky_2009, title={Extrinsic interface formation of HfO2 and Al2O3/GeOx gate stacks on Ge (100) substrates}, volume={106}, ISSN={["1089-7550"]}, DOI={10.1063/1.3204026}, abstractNote={The extrinsic interfaces present at the HfO2∕GeOx∕Ge and Al2O3∕GeOx∕Ge gate stacks are investigated. The effective trapped charge density, estimated from hysteresis in capacitance-voltage characteristics, is higher for HfO2 than for Al2O3, implying qualitatively different charge trapping sources in each dielectric. Spectroscopic ellipsometry and medium energy ion scattering measurements reveal that HfO2 deposition induces the formation of a thicker germanate (intermixed) layer at the HfO2∕GeOx interface, where nonstoichiometric Ge-rich GeOx having significantly low bandgap (∼1.8eV) is present. In contrast, Al2O3 deposition leads to an abrupt and thinner O-rich GeOx interfacial layer without Ge-rich GeOx phase. The proposed band alignment indicates that Ge-rich GeOx layer at HfO2∕GeOx arises a significant band potential well trapping, while O-rich GeOx layer in Al2O3∕GeOx is responsible for a relatively lower charge trapping at band potential well. The combined results strongly suggest that the control of the GeOx interface layers is crucial to reduce the high charge trapping at high-κ∕GeOx∕Ge gate stacks.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Seo, H. and Bellenger, F. and Chung, K. B. and Houssa, M. and Meuris, M. and Heyns, M. and Lucovsky, G.}, year={2009}, month={Aug} }
 @article{chung_lucovsky_lee_cho_jeon_2009, title={Instability of incorporated nitrogen in HfO2 films grown on strained Si0.7Ge0.3 layers}, volume={94}, ISSN={["0003-6951"]}, DOI={10.1063/1.3077014}, abstractNote={The interfacial characteristics and thermal stability of nitrided HfO2 films grown on strained Si0.7Ge0.3 layers were investigated by medium energy ion scattering, high-resolution x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure. N incorporation of HfO2 films grown on Si0.7Ge0.3 layers was strongly related to the diffusion of Si and Ge from strained Si0.7Ge0.3 layers in the interfacial region between HfO2 films and Si0.7Ge0.3 layers by the annealing treatment in NH3 ambient. The chemical states of SiOxNy and GeOxNy were formed in the interfacial region by N incorporation, and SiOxNy was dominant chemical states rather than that of GeOxNy. However, the incorporated N was not stable, which was mostly diffused out during the postnitridation annealing in a N2 ambient. The instability of incorporated N through the additional annealing treatment extensively caused the change in the structure of HfO2.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Chung, K. B. and Lucovsky, G. and Lee, W. J. and Cho, M. -H. and Jeon, Hyeongtag}, year={2009}, month={Jan} }
 @article{chung_lee_kim_cho_moon_2009, title={Nucleation Behavior of Atomic Layer Deposited SiO2 for Hf-Silicate Films}, volume={156}, ISSN={["0013-4651"]}, DOI={10.1149/1.3098496}, abstractNote={The nucleation and growth of SiO 2 , as a function of surface condition, was investigated using in situ medium-energy ion-scattering analysis. The amount of SiO 2 required for saturation on the thermal oxide and on the chemical oxide was found to be 0.75 and 3.84 X 10 14 Si/cm 2 , respectively. The growth of SiO 2 on the initial HfO 2 surface increased as a function of HfO 2 coverage and growth when the HfO 2 coverage over 1 monolayer (ML) becomes saturated when the coverage of SiO 2 is ∼7 X 10 14 Si/cm 2 , which corresponds to a coverage of 1 ML SiO 2 . The nucleation of SiO 2 greatly depends on the initial surface conditions. In addition, the nucleation of SiO 2 has a tendency to become saturated, regardless of the initial surface conditions.}, number={5}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Chung, Kwun-Bum and Lee, W. J. and Kim, C. Y. and Cho, Mann-Ho and Moon, Dae Won}, year={2009}, pages={G43–G47} }
 @article{seo_chung_long_lucovsky_2009, title={Preparation of Native Oxide and Carbon-Minimized Ge Surface by NH4OH-Based Cleaning for High-k/Ge MOS Gate Stacks}, volume={156}, ISSN={["1945-7111"]}, DOI={10.1149/1.3212848}, abstractNote={The native oxide and carbon-contaminant-minimized Ge surface with ammonium hydroxide (NH 4 0H)-based cleaning for high-k/Ge metal-oxide-semiconductor (MOS) gate stack application is reported. Furthermore, the carbon-free interfacial Ge-oxide layer preparation on the cleaned Ge surfaces was also studied. The thickness of GeO 2 on Ge surface before, during, and after different cleaning processes was evaluated by the spectroscopic ellipsometry measurements. The HF rinsing step in the cyclic HF/deionized water cleaning was not effective for a removal of native GeO 2 because it cannot form the soluble species by a chemical reaction in the low pH HF solution. A cyclic NH 4 OH-based cleaning results in a minimum residual GeO 2 at 3 and 8 A on Ge(111) and (100), respectively. The fast regrowth of GeO 2 on cleaned Ge surfaces under air exposure was observed, regardless of the cleaning methods. However, Auger electron spectroscopy spectra showed less amount of carbon on Ge surfaces with NH 4 OH-based cleaning than HF-based cleaning. The small amount of residual carbon after NH 4 OH-based wet cleaning was completely removed by O 2 plasma for a very thin ( ∼10 A) surface oxidation in the remote plasma-enhanced chemical vapor deposition chamber.}, number={11}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Seo, H. and Chung, K. B. and Long, J. P. and Lucovsky, G.}, year={2009}, pages={H813–H817} }
 @article{lucovsky_chung_kim_norlund_2009, title={Spectroscopic differentiation between O-atom vacancy and divacancy defects, respectively, in TiO2 and HfO2 by X-ray absorption spectroscopy}, volume={86}, ISSN={["0167-9317"]}, DOI={10.1016/j.mee.2009.03.005}, abstractNote={Defect state features have been detected in second derivative O K edge spectra for thin films of nano-crystalline TiO2 and HfO2. Based on soft X-ray photoelectron band edge spectra, and the occurrence of occupied band edge 4f states in Gd(Sc,Ti)O3, complementary spectroscopic features have been confirmed in the pre-edge (<530 eV) and vacuum continuum (>545 eV) regimes of O K edge spectra. Qualitatively similar spectral features have been obtained for thin films of HfO2 and TiO2, and these have been assigned to defect states associated with vacancies. The two electrons/removed O-atom are not distributed uniformly over the TM atoms defining the vacancy geometry, but instead are localized in equivalent d-states: a d2 state for a Ti monovacancy and a d4 state for a Hf divacancy. This new model for electronic structure provides an unambiguous way to differentiate between monovacancy and divacancy arrangements, as well as immobile (or fixed) and mobile vacancies.}, number={7-9}, journal={MICROELECTRONIC ENGINEERING}, author={Lucovsky, G. and Chung, K-B and Kim, J. -W. and Norlund, D.}, year={2009}, pages={1676–1679} }
 @article{suh_ko_cho_chung_2009, title={Study of Hafnium Silicate Treated with NO Gas Annealing}, volume={54}, ISSN={["1976-8524"]}, DOI={10.3938/jkps.54.637}, abstractNote={The physical and the electrical properties of nitrided hafnium-silicate lms treated with NO gas annealing were investigated using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption ne structure and capacitance-voltage measurements. We con rmed that nitrogen incorporation during the NO gas annealing treatment enhanced the thermal stability of Hf silicate. The suppression of phase separation was observed in hafniumsilicate lms with high nitrogen contents. Moreover, small hysteresis changes were observed in the C-V curves. The negative shift of the threshold voltage was caused by the incorporation of nitrogen in the hafnium silicate lms.}, number={2}, journal={JOURNAL OF THE KOREAN PHYSICAL SOCIETY}, author={Suh, Dong Chan and Ko, Dae-Hong and Cho, Mann-Ho and Chung, Kwun Bum}, year={2009}, month={Feb}, pages={637–642} }
 @article{suh_cho_lee_ko_chung_cho_2009, title={The Effect of NH3 on the Interface of HfO2 and Al2O3 Films on GaAs(100) Surfaces}, volume={12}, ISSN={["1944-8775"]}, DOI={10.1149/1.3193534}, abstractNote={We investigate the effects of heat-treatment under NH 3 ambient on the formation of Ga-O at the interface between GaAs and high-k dielectric materials deposited by atomic layer deposition. Compared with the heat-treatment under N 2 ambient, the monochromatic X-ray photoelectron spectroscopy analysis reveal that the formation of Ga-O is greatly suppressed under NH 3 ambient for HfO 2 on GaAs. However, the same experiments for Al 2 O 3 on GaAs show that the effect is negligible. We examine the different reaction mechanisms of the NH 3 nitridation processes for two different high-k dielectric materials on GaAs.}, number={10}, journal={ELECTROCHEMICAL AND SOLID STATE LETTERS}, author={Suh, Dong Chan and Cho, Young Dae and Lee, Yongshik and Ko, Dae-Hong and Chung, Kwun Bum and Cho, Mann-Ho}, year={2009}, pages={H376–H377} }
 @article{cho_kim_moon_chung_yim_ko_sohn_jeon_2008, title={Change in the interfacial reaction of Hf-silicate film as a function of thickness and stoichiometry}, volume={129}, ISSN={["0021-9606"]}, DOI={10.1063/1.2955461}, abstractNote={Medium energy ion scattering and high-resolution transmission electron microscopy are used to investigate the depth of the interfacial reaction of Hf-silicate film. The interfacial reaction is critically affected by the film thickness and the mole fraction of HfO2 in silicate film. The interfacial compressive strain generated at the surface of the Si substrate is dependent on the film thickness during the postannealing process in film with a thickness of ∼4nm. Finally, the phase separation phenomenon demonstrates critically different behaviors at different film thicknesses and stoichiometries because the diffusion of Si from interface to surface is dependent on these factors. Moreover, the oxidation by oxygen impurity in the inert ambient causes SiO2 top formation.}, number={3}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Cho, M. -H. and Kim, C. Y. and Moon, K. and Chung, K. B. and Yim, C. J. and Ko, D. -H. and Sohn, H. C. and Jeon, Hyeongtag}, year={2008}, month={Jul} }
 @article{lee_cho_chung_lee_kim_choi_chung_moon_2008, title={Effects of reoxidation on band alignment in N-incorporated SiON films as a function of sequential thermal annealing in NO and NH3}, volume={93}, ISSN={["1077-3118"]}, DOI={10.1063/1.2955835}, abstractNote={The effects of reoxidation on the band structure of N-incorporated SiON films were investigated as a function of thermal treatment in NO and NH3. Reoxidation-associated changes in band gap and valence band offset of the N-incorporated SiON films prepared by sequential thermal annealing in both NO and NH3 were less than those observed for the nitrided film prepared by thermal annealing in only NH3. The differences in band-alignment characteristics of the nitrided films that resulted from use of different nitridation methods were strongly related to the depth distribution of N and the chemical states of N bonded to Si.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Lee, W. J. and Cho, M. -H. and Chung, K. B. and Lee, Y. S. and Kim, D. C. and Choi, S. Y. and Chung, U. I. and Moon, J. T.}, year={2008}, month={Jul} }
 @article{kim_cho_cho_chung_an_kim_lee_ko_2008, title={Interfacial reaction of atomic-layer-deposited HfO2 film as a function of the surface state of an n-GaAs (100) substrate}, volume={93}, ISSN={["1077-3118"]}, DOI={10.1063/1.2996261}, abstractNote={The characteristics of interfacial reactions and the valence band offset of HfO2 films grown on GaAs by atomic layer deposition were investigated by combining high-resolution x-ray photoelectron spectroscopy and high-resolution electron transmission microscopy. The interfacial characteristics are significantly dependent on the surface state of the GaAs substrate. Polycrystalline HfO2 film on a clean GaAs surface was changed to a well-ordered crystalline film as the annealing temperature increased, and a clean interface with no interfacial layer formed at temperatures above 600°C. The valence band offset of the film grown on the oxidized GaAs surface gradually increased with the stoichiometric change in the interfacial layer.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Kim, C. Y. and Cho, S. W. and Cho, M. -H. and Chung, K. B. and An, C. -H. and Kim, H. and Lee, H. J. and Ko, D. -H.}, year={2008}, month={Nov} }
 @article{chung_seo_long_lucovsky_2008, title={Suppression of defect states in HfSiON gate dielectric films on n-type Ge(100) substrates}, volume={93}, ISSN={["0003-6951"]}, DOI={10.1063/1.3005422}, abstractNote={Defect states in HfO2 and HfSiON films deposited on Ge(100) substrates were studied by spectroscopic ellipsometry (SE) and x-ray absorption spectroscopy (XAS). In addition, structural and compositional changes in these films were examined via medium energy ion scattering (MEIS). SE and XAS experiments revealed two distinct band edge defect states, located at 1.7±0.1eV and at 2.7±0.1 below the conduction band edges of these films. The number of defect states in HfO2 increased noticeably following postdeposition annealing (PDA), whereas in HfSiON, it showed only small increases following the same treatment. MEIS measurements showed that Ge diffusion into HfO2 films was enhanced significantly by PDA as well; however, this effect was less pronounced in the HfSiON films. The suppression of defect state enhancement in HfSiON films was correlated with lower levels of Ge diffusion and increased structural stability with respect to HfO2.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Chung, K. B. and Seo, H. and Long, J. P. and Lucovsky, G.}, year={2008}, month={Nov} }
 @article{eom_hwang_kim_cho_chung_2008, title={Thermal annealing effects on the atomic layer deposited LaAlO3 thin films on Si substrate}, volume={11}, ISSN={["1944-8775"]}, DOI={10.1149/1.2916437}, abstractNote={The changes in film structure of amorphous atomic layer deposited LaAlO 3 thin films after thermal annealing were examined by medium-energy ion-scattering measurements and angle-resolved X-ray photoelectron spectroscopy. Thermal annealing induces Si-rich LaSiO and Al-deficient LaAl x Si y O z layers on a few monolayers of SiO 2 . Al atoms do not participate in silicate formation during annealing. Instead, they migrate toward the film surface, which induces nonhomogeneity in the films along the vertical direction. The concentrations of Al and La on the film surface increase and decrease, respectively, as a result of Si diffusion from the substrate and silicate formation.}, number={7}, journal={ELECTROCHEMICAL AND SOLID STATE LETTERS}, author={Eom, Dail and Hwang, Cheol Seong and Kim, Hyeong Joon and Cho, Mann-Ho and Chung, K. B.}, year={2008}, pages={G33–G36} }