Papers by Keyword: Porous Silicon (PS)

Abstract: We report the structural and photoluminescence properties of CdTe/Porous silicon (PS) composite system prepared by chemical vapor deposition. The XRD pattern accord with the standard pattern of cadmium telluride of the samples was evaluated and the morphology of CdTe particles was characterized by scanning electron microscopy. The composite sample gives a strong luminescence and the mechanism of photoluminescence with CdTe/PS has also been discussed.

Abstract: We have measured photoluminescence of porous silicon which is electrochemically prepared on single crystal silicon wafer with co-implantation of Ar+ and N+ ions. The results show that the photoluminescence intensity of porous structure of co-implanted silicon was enhanced that we attribute these to the enhanced formation of porous silicon microstructure induced by ion implantation and from the analysis by scanning electron microscopy, it is demonstrated that the different density of the pores with different doses ion implantation

Abstract: We report the structural and optical properties of a-Al2O3 film grown on porous silicon substrate using sol-gel method. The results indicated that a-Al2O3 film were grown after it sintering at 1200 °C for 1 hour and the scanning electron microscopy image shows the a-Al2O3 film has a nanostructure. From the photoluminescence spectrum, it shows that a narrow purple emission peak. This proved porous silicon is a good substrate to grow a-Al2O3 film.

Abstract: Mechanical degradation of mobile silicon components of complex MEMS reduces device reliability and operation time. Although the considerable wear of the surface micromachined poly-crystalline elements can be decreased by substitution of crystalline-silicon-based equivalent, there is still room for further improvement in device durability. The demonstration device is the recently presented 3D crystalline silicon micro-turbine formed by the combination of proton beam writing (PBW) and subsequent selective porous silicon (PorSi) etching. Similarly to the DRIE (deep reactive ion etching) process the novel technique is capable to provide elements of vertical walls of high aspect ratio. The 3D silicon components were uniformly covered with LPCVD Si3N4 protective layer. The Si3N4 coating improves the chemical and mechanical properties; strength, hardness and chemical resistance. The elaborated processing technology can easily be adapted for deposition of protective materials of superior properties, e.g. TiN and DLC (diamond like carbon). Present work describes alternative hard coating technique integrated in the MEMS processing sequence. The feasibility of the proposed technique is demonstrated by preliminary qualitative wear tests.

Abstract: The special physicochemical environment caused by sonic-vacating provides an important outlet for the preparation of highly efficient luminescent porous silicon films. Experimental results show that sonic—chemical treatment is an effective technology for the improvement of the microstructure of porous silicon, and the luminescent efficiency and stability thereof. Luminescent porous silicon films, prepared by ultrasonic—enhanced anode electrochemical etching, display better qualities than the samples prepared by conventional methods widely used at present. This ultrasonic—chemical effect roots in sonic—vacating, i.e. the generation, formation and rapid collapse of bubbles in the etching solution. In the process of the porous silicon being etched, the escape rate and caving-in of hydrogen bubbles in the pores is increased as a result of the work of the ultrasonic waves, which is helpful to the vertical etching of the pores.

Abstract: MEMS technology requires low cost techniques to permit large scale fabrication for production. Porous silicon (PS) can be used in different manner to replace standard expensive etching techniques like DRIE (Deep Reactive Ion Etching). To perform same process quality as the latter, one need to understand how different parameters can influence porous silicon properties. We investigate here local formation of macroporous silicon on 2D and 3D silicon substrates. The blank substrate is a low doped (26–33 Ω cm) n type 6 inches silicon wafer. Then, an in situ phosphorus-doped polycrystalline silicon (N+ Poly-Si) is deposited on a thermal oxide layer to delimit the regions to be etched. Porous silicon is obtained afterwards using electrochemical anodization in a hydrofluoric acid (HF) solution. The effect of the temperature process on Si-HF electrochemical system voltamperometric curves, macropores morphology and electrochemical etch rates is more specifically studied. Moreover, permeation of porous substrates to hydrogen is studied after various anodization post-treatments such as KOH and HF wet etching or after a thin gold layer deposition used as current collector in micro fuel cells.

Abstract: The microstructures of electrochemically-deposited copper control electrode on semiconducting porous silicon films were investigated with scanning electron microscopy. Our results showed that smooth control electrode could be grown in areas far from the edge of porous silicon film while irregular electrode was formed on the circular edge of porous silicon films. The self-similarity of the electrochemically-deposited copper control electrode was analyzed in details.

Abstract: Cu-Si nanocomposites formed by an immersion displacement deposition of Cu into porous silicon (PS) matrix have been experimentally studied. SEM and AES were used to investigate the structure and elemental composition of Cu-Si samples. The top part of the Cu-PS samples is shown to demonstrate the following structure: large faceted Cu grains at the top, a porous fine-grained copper film underneath the large grains, and the copper pointed rods extended from the surface into the PS layer. The top part of the silicon skeleton of the PS layer is converted into the copper by the etching followed by Cu displacement deposition. The porosity of the porous layer and displacement deposition times are found to form Cu-Si nanocomposites of various structures and various Cu-Si contents because of various extent of the silicon skeleton transformation into copper.

Abstract: For ordered porous silicon, the Born potential and phonon Green’s functions are used to investigate its Raman response, while the electronic band structure and dielectric function are studied by means of a sp3s* tight-binding supercell model, in which periodical pores are produced by removing columns of atoms along [001] direction from a crystalline Si structure and the pores surfaces are passivated by hydrogen atoms for the electronic band structure calculations. This supercell model emphasizes the interconnection between silicon nanocrystals, delocalizing the electronic and phononic states. However, the results of both elementary excitations show a clear quantum confinement signature, which is contrasted with that of nanowire systems. In addition, ab-initio calculations of small supercells are performed in order to verify the tight-binding results. The calculated dielectric function is compared with experimental data. Finally, a shift of the highest-frequency Raman peak towards lower energy is observed, in agreement with the experimental data.

Abstract: To investigate the optical properties in non-periodic dielectric systems, we study here the reflection of light from nanostructured porous-silicon-based period doubling heterostructures. The multilayered systems are fabricated in such a way that the optical thickness of each layer is one quarter of 650nm. The results for the optical reflectance are presented and compared with that of Fibonacci, Thue-Morse, and random structures fabricated under the same conditions. Numerical simulation for the reflectance along the lines of the transfer matrix approach is performed. In addition, optical reflection from Gaussian porous silicon multilayers is also briefly discussed. We find that porous silicon Period Doubling dielectric multilayers could demonstrate the optical properties similar to the classical periodic Febry-Perot interference filters with one or multiple resonant peaks, but with an advantage of having total optical thickness much lesser than that of the periodic structures.