Young K. Park

Memory window of highly c-axis oriented ferroelectric YMnO3 thin films

YMnO3 thin films have been sputtered with different O2 partial pressures from 0% to 20%. Only the YMnO3 sputtered without O2 can be crystallized along (001) c-axis orientation after annealing at 870 °C. Mixing 10%–20% O2 partial pressure in the sputtering ambient, the excess Y2O3 in the YMnO3 films suppresses the c-axis oriented crystallization. Effects of crystallization on the ferroelectric properties of Pt/YMnO3/Y2O3/Si (MEFIS) and Pt/YMnO3/Si (MFS) gate capacitors have been investigated. The memory window of the MEFIS capacitor is enhanced by the c-axis oriented crystallization of the YMnO3.YMnO3 thin films have been sputtered with different O2 partial pressures from 0% to 20%. Only the YMnO3 sputtered without O2 can be crystallized along (001) c-axis orientation after annealing at 870 °C. Mixing 10%–20% O2 partial pressure in the sputtering ambient, the excess Y2O3 in the YMnO3 films suppresses the c-axis oriented crystallization. Effects of crystallization on the ferroelectric properties of Pt/YMnO3/Y2O3/Si (MEFIS) and Pt/YMnO3/Si (MFS) gate capacitors have been investigated. The memory window of the MEFIS capacitor is enhanced by the c-axis oriented crystallization of the YMnO3.

Effects of Bi-Pt alloy on electrical characteristics of Pt/SrBi2Ta2O9/CeO2/Si ferroelectric gate structure

Interface morphology and electrical properties of Pt/SrBi2Ta2O9(SBT)/CeO2/Si ferroelectric gate structure are characterized by considering the interactions among Bi, O, and Pt atoms during annealing process. It is found that the interfacial roughness of the Pt/SBT might be reduced during the annealing at 800 °C because the bottom side of the Pt electrode reacts with Bi atoms outdiffused from the SBT and the Bi–Pt alloys are molten at 765 °C, and the metallic Bi atoms are consumed by forming Bi oxide. Additionally, the capacitance and memory window of the ferroelectric gate structure annealed at 800 °C decrease to 69% and 80% of those values of the as-deposited gate structure, respectively, due to the additional capacitance and the voltage drop at the low dielectric Bi-oxide capacitor. In contrast, the leakage current characteristics are improved by two orders of magnitude after annealing at 800 °C for 30 min.

Dependence of carbon incorporation on crystallographic orientation of GaAs and AlGaAs grown by metalorganic chemical vapor deposition using CBr4

The electrical properties of CBr4-doped GaAs and Al0.3Ga0.7As epilayers grown on GaAs substrates with various surface crystallographic orientations from (100) toward (111)A were investigated. Carbon incorporation into GaAs and AlGaAs epilayers was performed by atmospheric pressure metalorganic chemical vapor deposition using CBr4. The electrical properties of the epilayers showed a strong crystallographic orientation dependence. With an increase of the surface offset angle, the hole concentration of CBr4-doped GaAs and AlGaAs epilayers rapidly decreased showing a hump at (311)A. The trend of the hole concentration dependence on the offset angle was not changed with growth temperatures in the range of 550–650 °C. Carbon incorporation is much higher in AlGaAs than in GaAs.

Temperature-dependent Hall analysis of carbon-doped GaAs

The temperature dependence of the electrical properties, such as hole concentration, Hall mobility and resistivity of carbon-doped GaAs epilayers over a wide range of doping levels has been investigated. The carbon-doped GaAs epilayers have been grown by low pressure metalorganic chemical vapor deposition. The electrical properties have been obtained by Hall measurements. Experimental data on the carrier mobility, Hall effect, and resistivity over a wide temperature range have been analyzed and possible scattering mechanisms have been explained. Our experimental data show that the ionized impurity scattering tend to be dominant at temperatures below 100 K, while the lattice scattering as well as the ionized impurity scattering plays an important role at temperatures above 100 K. The dependence of the electrical on the doping levels has also been studied. In the case of heavily C-doped GaAs, the mobility curves are nearly flat at temperatures below 100 K and the mobility decreases as temperature increases above 100 K. The reason is that the degenerate conduction occurs at high doping level. The degenerate conduction begins at the hole concentration of about 2 × 1018 cm−3 at 77 K and at room temperature.

MASKLESS SELECTIVE EPITAXIAL GROWTH ON PATTERNED GAAS SUBSTRATES BY METALORGANIC CHEMICAL VAPOR DEPOSITION

Maskless one-step selective CCl4-doped GaAs epilayers have been grown on patterned GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition. The growth technique has potential for realizing a well-defined quantum confinement structure and lateral structure device. Round shaped CCl4-doped GaAs epilayer was selectively grown inside a U-groove and on the sidewalls of a mesa with a significant lateral growth rate enhancement, whereas no growth was observed outside U-groove and on top of the mesa.

Facet Evolution of Al0.5Ga0.5As/GaAs Multilayers Grown on Mesa-Patterned GaAs Substrate

Facet evolution of (511)A of Al0.5Ga0.5As/GaAs multilayers grown on a mesa-patterned GaAs substrate by metalorganic chemical vapor deposition has been investigated. The time development equation of the growth morphology together with the bond density model was introduced to analyze the facet evolution. The facets at the concave surface on the mesa-patterned GaAs substrate during the growth process were evolved toward the growth surface with the highest growth rate. The facets having the highest growth rate were analyzed as a function of the surface migration length. The calculated results show that the highest growth rate in the surface plane of (511)A occurred at the concave surface on a mesa-patterned GaAs substrate with a surface migration length of larger than 1.5 µm.

Large supercell molecular dynamics study of defect formation in hydrogenated amorphous silicon

Abstract We have performed molecular dynamics simulations of the defect formation associated with the Staebler–Wronski (SW) effect in a-Si:H using 224 and 231 atom supercells and employing semiempirical Si–Si and Si–H total energy functionals. The role of hydrogen in the defect formation within the bond breaking model of the SW effect has been investigated for both large supercells. The results suggest that, within this model, H can be important in weakening the normal Si–Si bonds which break to produce defects in the SW effect.

Improvement in diffusion barrier properties of PECVD W-N thin film by low energy BF2+ implantation

The structural and electrical properties of BF2+ implanted PECVD tungsten nitride thin film were investigated. After BF2+ implantation with 40keV and 1 X 1017 B ions/cm2, W-B+-N layer was formed at the surface region of W-N films. The ternary layer maintained the microcrystalline state and prevented nitrogen out-diffusion form W-N thin film after annealing at 800 degrees C for 30 min. The overall electrical resistivity of W-B+-N/W-N thin film is 200 (mu) (Omega) cm, which is higher than that of W-N thin film because of forming the ternary phase. BF2+ implanted tungsten nitride thin film improved thermal stability against Cu diffusion more than W-N thin film.

Effects of PECVD W-N diffusion barrier on thermal stress and electrical properties of Cu/W-N/SiOF multilevel interconnect

Effect of plasma enhanced chemical vapor deposition W-N diffusion barrier on characteristics of Cu based multilevel interconnect with fluorine doped silicon oxide (SiOF) was investigated. AFM results show that surface roughness of Cu film on the SiOF/Si increases 7.27 angstrom to 78.82 angstrom, whereas that of the Cu on the W-N/SiOF/Si, exhibiting smoother surface, increases from 12.49 to 45.31 angstrom after annealing at 500 degrees C for 30 min. Also, the resistivity of Cu/W-N/SiOF/Si system is lower than that of Cu/SiOF/Si after post-annealing. The stress evolution during the annealing at 200-500 degrees C reveals that the Cu and SIOF films have tensile stresses and the W-N film has low compressive stress. Therefore, Cu/W-N/SiOF/Si interconnect has lower tensile than that of Cu/SiOF/Si due to the low compressive stress of the W-N. C-V measurements show that in the Cu/SiOF/Si capacitor the threshold voltage shifts to -0.5 V after annealing at 500 degree C for 30 min. These results mean that the Cu atoms are diffused into the SiOF after post annealing and these Cu atoms act as positive ions in the SiOF. However, in the Cu/W-N/SiOF/Si the W-N prevents the diffusion of Cu atoms into the SiOF and the out diffusion of F from the SiOF.

Effect of atomic bond structure on crystallographic orientation dependence of carbon doping in GaAs

The effect of atomic bond structure at the deposition surface on the crystallographic orientation dependence of carbon doping in GaAs was studied. Carbon doping into GaAs epilayers was performed by atmospheric pressure metalorganic chemical vapor deposition using extrinsic carbon sources of carbon tetrachloride (CCl4) and carbon tetrabromide (CBr4). Epitaxial growths were done on the exact (100) and four different misoriented GaAs substrates with orientations of (511)A, (311)A, (211)A, and (111)A. The electrical properties were measured by van der Pauw Hall analysis at room temperature. Electrically active concentrations in excess of 1×1019 cm−3 were obtained so that 4 and CBrCCl4 were demonstrated as efficient p-type dopant sources for carbon doping into GaAs. The dependence of hole concentration on the offset angle of CCl4-doped and CBr4-doped GaAs shows the same tendency, whereas the trend of carbon doping from intrinsic carbon doping technique is different from our results. In particular, the hole con...