J. Y. Cheng

Structure and properties of epitaxial Ba0.5Sr0.5TiO3/SrRuO3/ZrO2 heterostructure on Si grown by off‐axis sputtering

We report the growth and characterization of epitaxial Ba0.5Sr0.5TiO3/SrRuO3/ZrO2 on Si for potential charge storage applications. Both Ba0.5Sr0.5TiO3 (BST) and SrRuO3 (SRO) are grown (110)‐oriented on yttrium‐stabilized ZrO2 (YSZ) (100)‐buffered Si. These films show a high degree of crystallinity with minimal interdiffusion at the interfaces as evidenced from x‐ray diffraction, Rutherford backscattering, and transmission electron microscopy. Studies on the in‐plane crystallographic relations between the layers revealed an interesting rectangle‐on‐cube epitaxy between BST/SRO and YSZ. The dielectric constant and loss tangent of the BST dielectric layer are 360 and 0.01 at 10 kHz, respectively. The leakage current density is lower than 4×10−7 A/cm2 at 1 V. A strong frequency dependence on both dielectric constant and loss tangent is observed in 1–10 MHz frequency range. This is attributed to the effect of a series resistance in the measurement loop, which is likely related to the bottom SrRuO3 electrode.

Liquid‐crystal orientational bistability and nematic storage effects

A new class of nematic liquid‐crystal storage effects with potential display applications is described. We have developed structures, produced by special surface alignment patterns, exhibiting bistable configurations. Switching between states has been demonstrated with both electric and magnetic fields. The movement of disclinations and the topological distinction between states play essential roles in bistable switching. The properties of the bistable states and a proposed switching mechanism are described.

The liquid‐crystal alignment properties of photolithographic gratings

The liquid‐crystal alignment properties of gratings with a 1–10‐μm period are described. Experiments are presented to compare the roles of interfacial interactions and surface topography in determining alignment. It is shown that grooves are neither necessary nor always sufficient to produce alignment. Interfacial forces can give rise to strongly pinned alignment, governed by various biases applied during the first appearance of long‐range order at the interface.

THE MECHANISM OF IRON GETTERING IN BORON-DOPED SILICON

High‐energy B implantation was used to introduce gettering layers into float‐zone Si wafers contaminated with 2×1014 Fe/cm3. Secondary ion mass spectrometry shows that about 5% of the Fe contamination is collected at the 4 μm deep peak of a 4×1014/cm2, 3.3 MeV B implant after annealing at 1000 °C for 1 h. Deep level transient spectroscopy demonstrates that increasing the gettering B dose from 4×1012 to 4×1014/cm2 reduces the Fe concentration from 3×1012 to below ∼1010/cm3 in the 1–3 μm deep region from the surface, indicating very efficient gettering. Measurements of the Fe depth profile imply that the depletion of Fe near the gettering layer occurs upon cooling down from 1000 °C. The gettering behavior can be qualitatively understood in terms of a Fermi‐level‐enhanced pairing reaction between Fe and B.

FORMATION OF EXTENDED DEFECTS IN SILICON BY HIGH ENERGY IMPLANTATION OF B AND P

The extended defects induced in silicon by high energy implantation (1.5 MeV B and 2.6 MeV P) have been investigated by plan‐view and cross‐sectional transmission electron microscopy studies and defect etching measurements. The threading dislocations were identified to be long dislocation dipoles generated in the region of the ion projected range which grew up to the surface. The formation of threading dislocations is shown to have a strong dependence on the implantation dose and O concentration. After 900 °C annealing, a high density of threading dislocations was formed for B and P implants in a dose range of 5×1013–2×1014 cm−2 and 5×1013–3×1014 cm−2, respectively. The threading dislocation density in B‐implanted Czochralski Si substrates was found to be much higher than that in B‐implanted epitaxial Si substrates. This difference is attributed to the strong pinning effect of oxygen immobilizing dislocations in Czochralski substrates. Because P impurities are also efficient at pinning dislocation motion ...

A nematic liquid crystal storage display based on bistable boundary layer configurations

We describe a new twisted nematic liquid crystal display effect exhibiting bistable equilibrium states under an applied field. Each state is characterized by a boundary layer configuration whose properties provide for optical differentiation of the states. The basic principles, optics, and switching properties of this device are discussed.

A scanning electron microscope study of columnar topography and liquid‐crystal alignment on obliquely deposited oxide surfaces at low rates

We present direct evidence of a columnar topography in obliquely deposited oxide films prepared by thermal and electron beam deposition at low rates. Column size, chaining, and inclination will be described and the correlations with liquid‐crystal surface tilt alignment discussed.

Low resistance Ohmic contact scheme (∼μΩ cm2) to p-InP

A low resistance Pd/Sb/Zn/Pd Ohmic contact based on the solid phase regrowth principle has been investigated to p-InP. Contact resistivity as low as ∼2×10−6 Ω cm2 has been obtained for samples annealed at 500 °C for 1 min. The Ohmic behavior can be rationalized by the formation of a heavily doped surface layer or a heterojunction. The InSb phase responsible for the observed low resistivity is identified using the x-ray diffraction technique.

Threshold and switching characteristics of a bistable nematic liquid‐crystal storage display

The electrical switching characteristics of a bistable liquid‐crystal storage display is described, including the response times, switching mechanism, and a field dependence that exhibits several threshold effects. The origins and properties of these thresholds are discussed in relation to their utility in matrix‐addressing applications.

Ohmic contact formation mechanism of the Au/Ge/Pd/n‐GaAs system formed below 200 °C

We report the ohmic contact formation mechanism of the low resistance (∼1×10−6 Ω cm2) Au/Ge/Pd contact to n‐GaAs annealed at 175 °C. Cross‐sectional transmission electron microscopy and Rutherford backscattering spectrometry were utilized in this study. It is found that the solid phase regrowth process, interdiffusion between Au and Ge, and the enhancement of the conductivity of the excess Ge layer are responsible for the observed low contact resistivity.