Bernard Gelloz

Stable electroluminescence of nanocrystalline silicon device activated by high pressure water vapor annealing

Electroluminescence (EL) and electrical properties of nanocrystalline porous silicon (PS) diodes have been sufficiently improved by introducing high pressure water vapor annealing into the active PS layer. The EL emission is significantly enhanced without affecting the operating voltage. In addition, the fabricated device shows no degradations in both the EL intensity and the diode current density under a dc operation. The EL spectra coincide well with the photoluminescence ones. The obtained high EL performance is presumably caused by complete passivation of nanocrystalline silicon surfaces by thin tunnel oxides with mostly unstrained uniform network and little interfacial trapping defects.

Energy transfer in porous-silicon/laser-dye composite evidenced by polarization memory of photoluminescence

The optical properties of nanocomposites are studied for rhodamine B RhB dye molecules embedded in nanoscale porous silicon PS and porous silica P-silica. The samples are prepared by simple immersion of porous matrix substrates in RhB solutions. Fourier transform infrared spectroscopy suggests that RhB molecules fully penetrate into the porous matrix. Efficient photoluminescence has been observed in all experimental nanocomposites. The measurement of the polarization memory PM effect provides a clear evidence for the presence of an excitation energy transfer from PS to RhB molecules, in contrast to the PM behavior in RhB /P-silica composite.

Stabilized porous silicon optical superlattices with controlled surface passivation

We report on very effective stabilization of porous silicon optical devices through a chemical surface modification technique. Such a chemical treatment proves to alter the growth of native silicon oxide on pore surfaces and thus prevents the optical device from chemical aging. As an example, we apply this technique to one-dimensional freestanding optical superlattices made of five coupled microcavities. We demonstrate how the transmission resonances of the superlattice stabilize after treatment, which implies that refractive indices in the multilayer structure remain constant. The effectiveness of the chemical surface modification technique guarantees a long-life functionality of porous silicon-based optical devices.

Operation of nanosilicon ballistic electron emitter in liquid water and hydrogen generation effect

The usefulness of the ballistic emitter in liquid has been studied for nanocrystalline silicon (nc-Si) diode. Here the authors show that the nc-Si ballistic emitter operates well in liquid water, and that hydrogen gas is produced from the device surface only by electron incidence into water without using any counterelectrodes. The mechanism of direct hydrogen generation is discussed in relation to the interaction between energy-tunable hot electrons and water. The present result develops a concept of electron emission device as an active electrode in liquid. Advantageous features and the usefulness of this effect are also addressed.

Long-lived blue phosphorescence of oxidized and annealed nanocrystalline silicon

It is shown that an appropriate combination of thermal oxidation and high-pressure water vapor annealing for nanosilicon leads to efficient blue-band phosphorescence with a lifetime of several seconds. Based on spectroscopic analyses on both the temperature dependence of decay dynamics and the change in the peak wavelength with the excitation energy, the phosphorescence is related to luminescence centers in nanosilicon network embedded within high-quality oxide. By controlled oxidation, slow blue transitions via triplets are revealed in nanosilicon separately from the conventional fast band.

Thin Cu Film Deposition by Operation of Nanosilicon Ballistic Electron Emitter in Solution

A thin solid-film deposition scheme is presented based on electron injection from a planar ballistic cold emitter into a metal―salt solution. Under the emitter operation in CuSO 4 solutions without using any counter electrodes, thin polycrystalline Cu films are uniformly deposited on the emitting area due to the reduction of Cu 2+ ions at the interface. By using the device with patterned emission line windows, a thin Cu nanowire array can be fabricated in parallel. The effect presented here provides an advanced wet processing not only for metallization but also for the deposition of various thin solid films.

Highly Efficient and Stable Photoluminescence of Nanocrystalline Porous Silicon by Combination of Chemical Modification and Oxidation under High Pressure

A combination of high-pressure water vapor annealing (HWA) and chemical modification (CM) was used in order to fully passivate the nanocrystalline silicon surface of porous Si (PS) and electrochemically oxidized PS. The effects of these treatments on the surface chemistry are characterized by Fourier transform infrared spectroscopy in relation to the respective photoluminescence (PL) properties. The use of both HWA and CM enables a higher PL intensity than that of only HWA. The order in which the treatments are implemented greatly affects the final nanostructure and PL characteristics. The marked enhancement in PL efficiency by HWA was confirmed. PL efficiency is further improved by additionally performing CM, owing to further enhancement of surface passivation. The highest PL intensity was obtained when CM was performed before HWA. This may be explained by the enhanced surface passivation together with a better preservation of Si nanocrystals. For all the modified samples, PL stability was considerably enhanced compared with that of the reference sample.

Reduction in surface recombination and enhancement of light emission in silicon photonic crystals treated by high-pressure water-vapor annealing

We propose and demonstrate the application of high-pressure water-vapor annealing (HWA) to silicon photonic crystals for surface passivation. We find that the photoluminescence intensity from a sample treated with HWA is enhanced by a factor of ∼6. We confirm that this enhancement originates from a reduction in the surface-recombination velocity (SRV) by a factor of ∼0.4. The estimated SRV is as low as 2.1×103u2002cm/s at room temperature. These results indicate that HWA is a promising approach for efficient surface passivation in silicon photonic nanostructures.

Highly Enhanced Efficiency and Stability of Photo- and Electro-luminescence of Nano-crystalline Porous Silicon by High-Pressure Water Vapor Annealing

The effects of high-pressure water vapor annealing (HWA) on the photoluminescence (PL) of quantum-sized silicon materials have been studied for as-anodized or electrochemically oxidized heavily doped n-type porous Si (PS) and electrochemically oxidized p-type PS. PL efficiency and stability are markedly enhanced in all HWA-treated samples. PL peak wavelength remains almost unchanged except for n+-type PS in which a large redshift in the PL emission band was observed due to a structural nonuniformity in the depth direction. The high PL efficiency and stability of HWA-treated PS are attributed mainly to a suppression of nonradiative defect density by complete passivation of silicon nanocrystal surfaces. On the basis of these results, HWA is employed to improve the electroluminescence (EL) characteristics. The device fabricated using an HWA-treated anodized pn+ junction shows improved EL efficiency and stability.

Polarization properties of scattered light from macrorough surfaces

We have characterized macrorough surfaces by measuring angle-resolved Stokes parameters of scattering. The analysis of the parameters as a function of a virtual scattering angle shows that polarization properties of the scattering in the plane of incidence display a very strong dependence on the surface roughness. The method and results of this analysis have a significant impact on the application of light scattering to the inspection and process-evaluation industry.