Dongping Wu

Surface-energy triggered phase formation and epitaxy in nanometer-thick Ni1−xPtx silicide films

The formation of ultrathin silicide films of Ni1-xPtx at 450-850 degrees C is reported. Without Pt (x=0) and for t(Ni)= 4 nm, polycrystalline NiSi films form and agglomerate at lower temperatures f ...

Density functional theoretical determinations of electronic and optical properties of nanowires and bulks for CdS and CdSe

The authors present density functionaltheoretical results of electronic and optical properties of wurtzite-type CdS and CdSesemiconductornanowires and bulks. The results show that quantum confinement will increase the energy gap, decrease the dielectric function, change the sign of birefringence, and increase the absolute value of birefringence at low-frequency region, as the dimensions of CdS and CdSe are reduced from the bulk to a nanowire with diameter of several nanometers. The optical spectral peaks of CdSenanowires show redshifts as compared with the corresponding ones of CdSnanowires.

Low-temperature switching fatigue behavior of ferroelectric SrBi2Ta2O9 thin films

The ferroelectric hysteresis and fatigue behavior over a wide temperature range from 290 to 50 K for SrBi2Ta2O9 thin films with Pt electrodes on silicon substrates, prepared by metalorganic decomposition (MOD) and pulsed-laser deposition (PLD), are investigated. It is found that given a fixed electrical field amplitude, the coercivity of all films increases with decreasing temperature T. The saturated hysteresis loop easily obtained for the MOD-prepared thin films has its remnant polarization enhanced with decreasing T, but the PLD-prepared samples exhibit minor loops whose remnant polarization decays with decreasing T. While the films prepared by MOD exhibit improved fatigue resistance at low T, significant fatigue effect at low T is observed for the films prepared by PLD. Although we cannot rule out the effect of strain, the experimental results can be explained by competition between pinning and depinning of domain walls, which are dependent of temperature and defect charges.

Ultra-shallow junctions formed using microwave annealing

Microwave annealing is shown to be viable for achieving low thermal budget formation of ultra-shallow junctions. Regrowth of a 10 nm thick amorphous Si layer that is generated during a Ge amorphization process prior to BF2 or As dopant implantation proceeds at rates up to 0.53 nm/min for BF2 and up to 0.33 nm/min for As at 370 °C. The fraction of electrical activation for implanted dopants is as high as 13% for BF2 and 32% for As with negligible diffusion at 540 °C.

A graphene field-effect capacitor sensor in electrolyte

The unique electronic properties of graphene are exploited for field-effect sensing in both capacitor and transistor modes when operating the sensor device in electrolyte. The device is fabricated using large-area graphene thin films prepared by means of layer-by-layer stacking. Although essentially the same device, its operation in the capacitor mode is found to yield more information than in the transistor mode. The capacitor sensor can simultaneously detect the variations of surface potential and electrical-double-layer capacitance at the graphene/electrolyte interface when altering the ion concentration. The capacitor-mode operation further facilitates studies of the molecular binding-adsorption kinetics by monitoring the capacitance transient.

Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing

Microwave annealing (MWA) is investigated as an alternative technique to rapid thermal processing with halogen lamp heating (RTP) for low-temperature silicide formation on epitaxially grown Si0.81Ge0.19 layers. Phase formation, resistivity mapping, morphology analysis, and composition evaluation indicate that the formation of low-resistivity NiSi1−xGex by means of MWA occurs at temperatures about 100 °C lower than by RTP. Under similar annealing conditions, more severe strain relaxation and defect generation are therefore found in the remaining Si0.81Ge0.19 layers treated by MWA. Although silicidation by microwave heating is in essence also due to thermal effects, details in heating mechanisms differ from RTP.

A theoretical investigation of hyperpolarizability for small GanAsm (n+m=4–10) clusters

In this paper, the second and third order polarizabilities of small Ga(n)As(m) (n + m=4-10) clusters are systematically investigated using the time dependent density functional theory (TDDFT)6-311+G* combined with the sum-over-states method (SOSTDDFT6-311+G*). For the static second order polarizabilities, the two-level term (beta(vec.2)) makes a significant contribution to the beta(vec) for all considered Ga(n)As(m) clusters except for the Ga3As4 cluster. And, for the static third order polarizabilities, the positive channel (gamma(II)) makes a larger contribution to gamma(tot) than the negative channel (gamma(I)). Similar to the cubic GaAs bulk materials, the small Ga(n)As(m) cluster assembled materials exhibit large second order (1 x 10(-6) esu) and third order susceptibilities (5 x 10(-11) esu). The dynamic behavior of beta(-2omega; omega, omega) and gamma(-3omega; omega, omega, omega) show that the small Ga(n)As(m) cluster will be a good candidate of nonlinear optical materials due to the avoidance of linear resonance photoabsorption.

On Different Process Schemes for MOSFETs With a Controllable NiSi-Based Metallic Source/Drain

This paper focuses on different silicidation schemes toward a controllable NiSi-based metallic source/drain (MSD) process with restricted lateral encroachment of NiSi. These schemes include thickness control of Ni, Ni-Pt alloying, and two-step annealing. Experimental results show that all the three process schemes can give rise to effective control of lateral encroachment during Ni silicidation. By controlling tNi, NiSi-based MSD metal-oxide-semiconductor field-effect transistors (MOSFETs) of gate length LG = 55 nm are readily realized on ultrathin-body silicon-on-insulator substrates with 20-nm surface Si thickness. With the aid of dopant segregation (DS) to modifying the Schottky barrier heights of NiSi, both n- and p-type MSD MOSFETs show significant performance improvement, compared to reference devices without DS.

TDHF-SOS treatments on linear and nonlinear optical properties of III-V semiconductor clusters (Ga3As3, Ga3Sb3, In3P3, In3As3, In3Sb3)

Abstract We employ an ab initio time-dependent Hartree–Fock (TDHF) formalism combined with sum-over-states (SOS) method to calculate the linear and nonlinear optical properties of direct semiconductor clusters. The obtained electronic absorption spectra predict a variety of the spectral shapes and peak positions and an increase of the second-order nonlinear optical response with an increase of V-group ionic radius in the title clusters. Charge transfers from the π bonding to π antibonding orbitals between III and V group atoms make a significant contribution to the second-order polarizability.

First-principles study: size-dependent optical properties for semiconducting silicon carbide nanotubes

Using first-principles calculations, we investigate the effect of tube size on optical properties of the zigzag, armchair, and chiral SiC nanotubes. The results indicate that the optical spectra of SiC nanotubes are dependent on the diameter and chirality, and that optical anisotropy is observed for different light polarizations. For a given chirality of SiCNTs, redshifts or blueshifts of the peaks in the dielectric function and energy loss function with increasing tube diameter are possible due to the competition between the size effect and pi orbitals overlapping, and the shifts become smaller as the tube diameter increases. The unusual optical properties of semiconducting SiC nanotubes present an opportunity for applications in electro-optical devices.