The effects of a combination of thermal oxidation at various temperatures and high-pressure water vapor annealing (HWA) on the luminescence and structural characteristics of nanocrystalline porous Si (PSi) have been investigated. The influences of initial PSi porosity and excitation power have also been studied. Strong, stable, and single-band blue emission was obtained when PSi was first treated by thermal oxidation above 800 C and then by HWA. This blue emission can coexist with the conventional red emission band of Si nanocrystals when PSi is not sufficiently oxidized. The blue emission may originate from localized states in the Si oxide or at the silicon/ oxide interface. HWA very efficiently boosts the emission from these localized states by increasing the quality of the oxide network. This result is useful for the realization of short-wavelength Si-based optoelectronic devices.

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To enhance the usefulness of ballistic hot electron injection into solutions for depositing thin group-IV films, a dripping scheme is proposed. A very small amount of SiCl 4 or GeCl 4 solution was dripped onto the surface of a nanocrystalline Si (nc-Si) electron emitter, and then the emitter is driven without using any counter electrodes. It is shown that thin Si and Ge films are deposited onto the emitting surface. Spectroscopic surface and compositional analyses showed no extrinsic carbon contaminations in deposited thin films, in contrast to the results of a previous study using the dipping scheme. The availability of this technique for depositing thin SiGe films is also demonstrated using a mixture SiCl 4 +GeCl 4 solution. Ballistic hot electrons injected into solutions with appropriate kinetic energies promote preferential reduction of target ions with no by-products leading to nuclei formation for the thin film growth. Specific advantageous features of this clean, room-temperature, and power-effective process is discussed in comparison with the conventional dry and wet processes.

An alternative wet process for depositing thin Si and Ge films is presented based on the ballistic electron injection into solutions. A nanocrystalline silicon (nc-Si) diode, composed of a thin Au (10 nm), nc-Si layer (~1 µm), polycrystalline silicon, and n + -Si substrate, operates as a surface-emitting active cold cathode in solutions. When driven alone in SiCl 4 and GeCl 4 solutions without using any counter electrodes, quasi-ballistic electrons generated in the nc-Si layer and ejected from the outer surface directly reduce Si and Ge ions followed by the deposition of thin amorphous Si 4+ and Ge 4+ films on the emitting surface with neither byproducts nor contaminations. Based on the structural and compositional characterizations of deposited Si and Ge films, the specific features of this deposition mode are discussed in comparison with the conventional dry process.

The presence of a magnetic field during anodization of Si in HF solution can drastically influence the resulting porous Si morphology. The effect of the strength of the magnetic field was investigated. The magnetic field enables the realization of non-percolating straight pores of diameters from 100 nm with n+-type Si to several micrometers for p-type Si, through depths as large as 100 μm, without any lithographic or pore initiation process. There is a clear enhancement of the pores aspect ratio when increasing the magnetic field strength, which enhances the collection of holes at the pore tips with respect to lateral pore walls. Thick, well-defined free-standing membranes can also been fabricated for applications such as bio-scaffold and filters.