Bui Huy

Effect of electrochemical etching solution composition on properties of porous SiC film

Porous amorphous SiC (a-SiC) layer with pore size in the nanometer region was fabricated on the a-SiC/Si substrates by the electrochemical etching method using HF/H2O/surfactant solution. Systematic study showed that the HF concentration in the etching solution (in the 1–73% region) strongly affects the structure (both the pore size and the pore density) of the porous a-SiC layer. It was also observed the changing of the photoluminescence properties of the porous a-SiC layer when its structure has been changed.

Silicon–Rich Silicon Oxide Thin Films Fabricated by Electro-Chemical Method

Porous silicon (PS) has attracted increasing research interest in basic physics as well as applications since 1990 when Canham reported on the efficient visible photoluminescence (PL) of porous silicon (Canham, 1990). Structurally, PS consists of many pores and silicon residuals and usually can be described as a homogeneous mixture of silicon, air and, even silicon dioxide. Based on porosity, PS can be classified into three types: nano, mesoand macro-pores. In the case of PS nano-pores, the size of both the silicon residuals and the air voids (pores) can be in the range of few nanometers. The exciton Bohr radius in Si is around 4.3 nm, so that quantum confinement can occur and change the electronic structure of those silicon nanocrystals. On the other hand, because the value of porosity is directly linked to the effective index of refraction of the PS layer, this layer appears as an effective medium, where the refractive index has a tunable value between the index of refraction of bulk Si and that of the air (pores). Those changes in the electronic structure and refractive index of PS when compared with bulk Si make it fascinating as both a low-dimensional material and an optical one. The considerable and controllable changes in the electronic structure and refractive index of PS fabricated by electrochemical anodization make it a promising material for photonics in comparison with bulk silicon and/ or pure silica. Using the oxidation process in O2 environment at high temperature, the PS samples become siliconrich silicon oxides (SRSO), which has high chemical instability and avoids the aging of the PS that is important condition for optical devices such as planar optical waveguides, optical interference filters, micro-cavities, etc (Bettotti et al., 2002). During the last decade, Erbium (Er)-doped silicon-rich silicon oxide has attracted much interest due to its big potential application in Si-based optoelectronic devices for telecom and optical sensors. The Er-ions implanted in SRSO materials produce light emission at around wavelength range of 1540 nm, which corresponds to minimum light absorption in silica-based glass fibers. In this regard, a lot of studies have been carried out to improve the luminescence efficiency of this material. Such studies have revealed that co-implantation of Er and O2 induce a strong enhancement in the Er-ions related emission at range of 1540 nm. In first case, samples were prepared by co-implanting Si and Er into silica thin films or co-sputtering Si, Er2O3 and SiO2 on the silicon substrate (Shin et al., 1995). In second case, samples were prepared by implanting Er-ions into SiO2 films containing Si-nanocrystals (nc-Si) and/or by Er-ion electrochemical deposition on silicon-rich oxide (SRSO) layers. The room temperature luminescence emission at the range of 1540 nm from Er-electrochemically doped porous

Porous silicon as a promising material for photonics

Electrochemical etching – a usual technique in nanotechnology – creates porous silicon with novel and useful properties. The considerable and controllable changes in the electronic structure and refractive index of porous silicon make it a promising material for photonics in comparison with bulk silicon. In this paper, we review as well as report on some interesting and unique properties of porous silicon material. In studying porous silicon as a low-dimensional material, we focus on the effect of the surface passivation of silicon nanocrystals on photoluminescence characteristics of such zero-dimensional crystals. As an optical material, we demonstrate the fabrication method and optical properties of the planar waveguide as well as the active waveguide and optical interference filters operated in infrared wavelengths. In addition, we investigated the effect of energy transfer from silicon nanocrystals to erbium ions in the erbium-doped porous silicon waveguide and also elaborate on the origins of the difference between the reflectivity spectra from fabricated filters and that of the simulation program.

Porous silicon as a low dimensional and optical material

The considerable and controllable changes in electronic structure and refractive index of porous silicon fabricated by electrochemical anodization make it become a promising material for photonics in comparison with bulk silicon. As the study of PS in terms of a low-dimensional material, we reviewed the effect of the surface passivation of silicon nanocrystals on photoluminescence spectra of such zero-dimensional crystals. In terms of an optical material, we show the fabrication method and optical properties of planar waveguide as well as active waveguide operated in the range of 1.54 μm wavelengths. We have also investigated the effect of energy transfer from silicon nanocrystals to erbium ions based on erbium-doped porous silicon waveguide.

Investigation of 1d Photonic Crystal Based on Nano-porous Silicon Multilayer for Optical Filtering

We present the fabrication, simulation, and measurements of 1D photonic crystal based on nano-porous silicon multilayer designed as an optical interference filter. Using electro-chemical etching with timely repeat steps of applied current densities, we fabricated a multilayer structure composed of alternating high- and low-index layer which achieved 90% power reflectivity at wavelength range of 1400-3000 nm. The simulation is relying on the Transfer Matrix Method (TMM) to design and predict the optical properties of nano-porous silicon multilayer as well as the relation between anodization parameters with reflection spectra. The measured reflection and transmission spectra of the nano-porous silicon multilayer show good agreement with simulation. This technique could provide a convenient and economical method to produce filters, cavities, and graded-index dielectric waveguides in the future.

Effect of Excitation Migration and Upconversion in Highly Erbium-doped Glass Micro-sphere Lasers

Excitation migration and upconversion process in the Erbium-doped silica-alumina glass microsphere lasers with concentrations of 2500-4000 ppm were investigated in detail. The experiment shows that under 976 nm excitation, the intense of up-conversion emission at 523, 546 and 657 nm, corresponding to the transitions 2H11/2 → 4I15/, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2, respectively, depends on the erbium content, migration of excitation and pump power. The excitation migration has strongly influenced on the threshold and Red shift of lasing wavelength and migration-assisted up-conversion process leads to degraded amplification performance of microsphere lasers made by silica-alumina glasses with different contents of Er-ions.

Fabrication and optical properties of erbium-doped silicon-rich oxide planar waveguides

In this article we describe the electrochemical method for fabricating Erbium-doped silicon-rich oxide (SRO) planar waveguides. The porosity, Er-ion concentration and the refractive index can be controlled by varying the current density (continuous or pulse currents) during the production process. The refractive index difference between the core and the cladding layers and the profile of SRO waveguides tested by m-line spectrometer and by FE-SEM. The photo-luminescent (PL) emission of Er-ions at 1550 nm in the SRO waveguides can be obtained even when the excitation wavelength was away from resonance absorption band of Er-ions. This result revealed that the observed emission at 1550 nm is possible due to the energy transfer from excitons confined in the nc-Si to Er-ions. The Er-doped SRO waveguides can be applied to optoelectronic devices compatible to Si-based integrated circuit technology.

Time-resolved luminescence spectrum and radiation recombination progress in surface and core of porous silicon

Time-resolved luminescence spectra (TRLS) of porous silicon (PS) in the delay time range of 10/sup -9/-10/sup -6/ s were investigated. The luminescence spectra include the blue zone with decay time of the order of nanoseconds and the red zone with longer decay time. Recombination mechanisms in the core and in the surface states were used to explain this experimental result. The existence of discrete peaks in the blue zone shows that the luminescence is due to nano-scale crystals.