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One of the most important properties of the porous silicon is its strong visible photoluminescence. However the intensity and the shape of the photoluminescence is changing as the sample ages, due to absorption of oxygen and hydrogen in the skeleton of the porous layer. This is why a good passivation for the porous silicon is crucial in order to fabricate a stable and reliable device with well-defined characteristics. Porous silicon was exposed to an ultrasonic treatment in order to increase the photoluminescence intensity and to passivate the layer. In this work we show that the ultrasound treatment increases the photoluminescence intensity by a factor of 2–3 in a very short period of time (10 min). Long ultrasound treatment results in a smaller increase of the photoluminescence intensity but dramatically slows the aging process of the porous silicon. We believe that the ultrasonic treatment introduces some energy to the porous silicon, allowing the traps in the skeleton to be repopulated. In this process, the deeper traps get occupied while the shallower traps are kept free, allowing the photoluminescence to increase and the aging process to decay. [ABSTRACT FROM AUTHOR]

Porous silicon formed on polished p-type (100) silicon wafers was subjected to a NF3/UV photo-chemical treatment at 300 °C and 400 °C at 60 Torr. When the treated porous silicon surface contacted with the ambient air at room temperature two amazing effects were observed: (i) a drastic increase of the s-band photoluminescence by 1–2 orders of magnitude; (ii) spontaneous room temperature growth of crystalline silicon dioxide SiO2. The growth of crystalline silicon dioxide was demonstrated by AFM and SEM images and proved by X-ray diffraction. A tridymite orthorhombic configuration of SiO2 was found. The size of the crystallites reached several micrometer after a few days aging at room temperature. The size and density of the crystals can be affected by the NF3 treatment temperature as well as by slight heating (75 °C) during aging. The rapid growth of the SiO2 layer is supposed to be due to the NF3/UV photo-thermal etching of the as-formed native oxide, as well as to the cleaning and enrichment of the porous silicon surface with fluorine. The latter can induce a catalytic action on the crystallization process. The formation of a better interface between porous silicon and the oxide (PS/SiO2) as compared to the not treated porous silicon covered by the non-stoichiometric SiOx (x ≉ 1) layer is claimed to cause a strong photoluminescence enhancement. [ABSTRACT FROM AUTHOR]

In the last ten years the interest in porous silicon electro-optics devices has been growing due to the promise to integrate VLSI silicon technology with optical input and output signals. The optical signals that do not have the delays of the RC electrical wires could help the VLSI chip to communicate much faster with its adjacent chips. The monolithic integration of the opto-electronic interface is a big challenge but would have the advantage of creating a complete system on the chip. The ability to control the refractive index of the porous silicon both in the lateral and in the longitudinal direction makes the material very attractive for electro-optics components like: filters, mirrors, wave-guides, and couplers. The multiplexers and demultiplexers being exhibited here are applications that could be used for example in VLSI for distributing synchronizing clocks without RC delay or focusing more then one signal to a single detector. The usage of porous silicon in the standard VLSI technology allows the designer more flexibility in choosing the optical properties of the required layers in a specific application. [ABSTRACT FROM AUTHOR]