An Ji

Electrical properties and thermal stability of Pd-doped copper nitride films

Pd-doped copper nitride films with Pd concentrations up to 5.6 at. % were successfully synthesized by reactive magnetron sputtering of metal targets. Higher concentration of Pd (>5.6 at. %) would deteriorate the quality of the deposits. XPS and XRD data strongly suggest that Pd atoms occupy the centers of the Cu3N unit cells rather than simply substituting for the Cu atoms. A reduction in the electrical resistivity by three orders of magnitude was observed when the Pd concentration increases from zero to 5.6 at. %. All the deposits with the Pd concentration up to 5.6 at. % exhibit n-typed conductivity behavior. The corresponding carrier concentrations increase by four orders of magnitude from 1017 to 1021u2009cm−3. Compared with the undoped copper nitride films, a weakly Pd-doped Cu3N films possess fine thermal stability in vacuum. And the decomposition product after annealing at 450u2009°C exhibits a good metallic behavior, indicating that it qualifies the fabrication of conduct wires or metallic structures for ...

Influence of the light trapping induced by surface plasmons and antireflection film in crystalline silicon solar cells

In this paper, silicon solar cells with Ag nanoparticles deposited on a SiO2 spacer were studied concentrating on the influence of the surface plasmon and the antireflection film. We experimentally found that the photocurrent conversion efficiency of the solar cell decorated by random arrays of self-assembled Ag nanoparticles increases firstly and decreases afterwards with increasing spacer thickness. Further investigations on the external quantum efficiency (EQE) illustrated this trend more clearly. It was also found that the effect of the surface plasmon on light absorption dominates over that of the antireflection film at the resonance wavelength which is an important factor determining the light trapping. Moreover, surface plasmon is determined by both the Si substrate and the SiO2 spacer. For self-assembled Ag particles on the surface of the solar cells in our experiments, appropriate spacer thickness (9-35 nm) could broaden the plasmon resonance, narrow the photocurrent suppression range, weaken the suppression amplitude and strengthen the gain at the resonance wavelength, while still providing antireflection effect.

Low temperature growth of amorphous Si nanoparticles in oxide matrix for efficient visible photoluminescence

We report a low temperature procedure for the fabrication of highly luminescent silicon nanoparticles in silicon-rich oxide films. A number density over 1012∕cm2 has been achieved for silicon particles of about 3nm in size by plasma-enhanced chemical vapor deposition at a substrate temperature of 30°C. Such deposits, when post-annealed at 500°C for 2 min, manifested a photoluminescence two orders of magnitude more intense than those samples grown at 250°C. Strong photoluminescence in the whole visible light range has been measured in samples prepared with this low-temperature procedure. The present results indicate the feasibility of fabricating silicon-based light-emitting devices with moderate processing temperatures.

Dielectric layer-dependent surface plasmon effect of metallic nanoparticles on silicon substrate

The electromagnetic interaction between Ag nanoparticles on the top of the Si substrate and the incident light has been studied by numerical simulations. It is found that the presence of dielectric layers with different thicknesses leads to the varied resonance wavelength and scattering cross section and consequently the shifted photocurrent response for all wavelengths. These different behaviours are determined by whether the dielectric layer is beyond the domain where the elcetric field of metallic plasmons takes effect, combined with the effect of geometrical optics. It is revealed that for particles of a certain size, an appropriate dielectric thickness is desirable to achieve the best absorption. For a certain thickness of spacer, an appropriate granular size is also desirable. These observations have substantial applications for the optimization of surface plasmon enhanced silicon solar cells.

Optimization of the Dielectric Layer Thickness for Surface-Plasmon-Induced Light Absorption for Silicon Solar Cells

In this study, we investigate the effect of dielectric layer thickness on light reflection due to random self-assembled Ag nanoparticles with diameters of less than 160 nm deposited on the Si substrate, indicating that a dielectric layer with an appropriate thickness is useful for reducing the amount of reflected light. In the short wavelength range, reflectivity is determined by the metallic plasmon and the SiO2 antireflection layer, and the effect of the surface plasmon dominates over the antireflection effect. In the long wavelength range, reflectivity decreases with increasing dielectric layer thickness and is determined by the oxide antireflection layer, while the effect of the surface plasmon is negligibly small. Moreover, the surface plasmon is affected by the SiO2 layer and Si substrate when the dielectric layer is thin; however, it is only determined by the SiO2 layer when the oxide layer is sufficiently thick. These observations have substantial applications for the optimization of surface-plasmon-enhanced silicon solar cells.

Fully lithography independent fabrication of nanogap electrodes for lateral phase-change random access memory application

A nanogap electrode fabrication method was developed and nanogap electrode as small as 17 nm was achieved based on sacrificial spacer process and conventional lithography. We have transferred this method to lateral phase-change random access memory (PCRAM) device fabrication. The electrical characterizations of 4.6u2002μm gap width using conventional lithography and 88 nm width based on this technology are shown. It is found that the threshold voltage and the dc power consumption are remarkably decreased due to nanogap electrode process. Our method cannot only improve the fabrication efficiency of PCRAM but also be easily transferred to other nanoelectronics applications.

Visible light emission from innate silicon nanocrystals in an oxide matrix grown at low temperature

Silicon nanocrystals with well-controlled sizes below 5.0xa0nm at a number density up to 1012xa0cm−2 were directly grown in hydrogenated silicon oxide films by plasma-enhanced chemical vapour deposition using SiH4, O2 and H2 as the precursor. For the immediate formation of silicon nanocrystals in deposits on a cold substrate, high-density hydrogen ions have to be maintained in the plasma. These innate silicon nanocrystals are found to be well isolated from each other and dispersed uniformly throughout the deposits. Intense visible photoluminescence was measured at room temperature from such samples, with the photon energy at about 1.67xa0eV being indifferent to the variation in particle size. The photoluminescence features can find a qualitative explanation in the nearly stabilized electronic states of silicon nanocrystals by Si = O surface-passivation.

Electron transport characteristics of silicon nanowires by metal-assisted chemical etching

The electron transport characteristics of silicon nanowires (SiNWs) fabricated by metal-assisted chemical etching with different doping concentrations were studied. By increasing the doping concentration of the starting Si wafer, the resulting SiNWs were prone to have a rough surface, which had important effects on the contact and the electron transport. A metal-semiconductor-metal model and a thermionic field emission theory were used to analyse the current-voltage (I-V) characteristics. Asymmetric, rectifying and symmetric I-V curves were obtained. The diversity of the I-V curves originated from the different barrier heights at the two sides of the SiNWs. For heavily doped SiNWs, the critical voltage was one order of magnitude larger than that of the lightly doped, and the resistance obtained by differentiating the I-V curves at large bias was also higher. These were attributed to the lower electron tunnelling possibility and higher contact barrier, due to the rough surface and the reduced doping concentration during the etching process.

A self-aligned process for phase-change material nanowire confined within metal electrode nanogap

A self-aligned fabrication process is presented by which phase-change material nanowire (NW) perfectly confined within metal electrode nanogap based on electron-beam lithography and inductively coupled plasma etching process. Lateral phase-change random access memory device fabrication is demonstrated by this process with Ge2Sb2Te5 NW confined within 39 nm tungsten electrode nanogap and the electrical characterizations are illustrated. It is found that the threshold current is only 2 μA and the dc power consumption is remarkably low. The process is simple, flexible and achieves localization filling. In addition, the process can be easily transferred to other types of phase-change and nanoelectronics materials.

Selective and lithography-independent fabrication of 20 nm nano-gap electrodes and nano-channels for nanoelectrofluidics applications

A new method has been developed to selectively fabricate nano-gap electrodes and nano-channels by conventional lithography. Based on a sacrificial spacer process, we have successfully obtained sub-100-nm nano-gap electrodes and nano-channels and further reduced the dimensions to 20 nm by shrinking the sacrificial spacer size. Our method shows good selectivity between nano-gap electrodes and nano-channels due to different sacrificial spacer etch conditions. There is no length limit for the nano-gap electrode and the nano-channel. The method reported in this paper also allows for wafer scale fabrication, high throughput, low cost, and good compatibility with modern semiconductor technology.