Study On Photoelectric Function And Application Of Porous Silicon Electrode

Porous silicon (PS) is a new type silicon-based material developed in recent years, which has different properties compared with the crystalline silicon materials. Porous silicon can emit luminescence efficiently across the whole range from the near infrared, through the visible region, to the near UV region. This characteristic makes it possible to fabricate light-emitting devices and solve the key problem of the optoelectronic integrated circuit (OEIC), opening up the bright future for the very large integrated circuit (VLIC).Bulk silicon, with indirect band gap of 1.12 eV, doesn't emit visible light at room temperature. With a broad and likely direct band gap, porous silicon has a different band structure from that of the bulk silicon. Thus the porous silicon can emit visible light at room temperature. Several methods commonly used in preparing porous silicon have been reviewed. Photoluminescence and electroluminescence (EL) properties of porous silicon in literature are summarized. Qualitative description has been presented for the prevalent mechanisms proposed to explain the bright PL and EL. The main contents are as following:1. Treatment of the porous silicon by H2O2 solutionThis study modifies the components for the electrolyte solution by adding H2O2 during electrochemically etching. Metallurgical microscope showed that porous silicon surface is relatively smooth, dense, uniform, and the oxidation of nano-particles is relatively small. An enhancement of photoluminescence from the modified porous silicon has been observed. Scanning electron microscopy (SEM) images indicated that there are more detached zones in the modified porous silicon surface than in generally etched porous silicon samples. The photoluminescent intensity is directly proportional to the bonds of Si-O and Si-O-Si, which were detected by Fourier transform infrared spectra (FTIR). The enhancement of photoluminescent intensity of the porous silicon might attributed to the decrease of the surface states, which are non-radiation recombination centres, caused by hanging bonds on the as-prepared porous silicon due to the formation of Si/SiOx (x≤2) interface.2. The effects of adding titanium sol during forming and photoelectric performance of the porous siliconThe common way for the production of porous silicon (PS) is the anodic etching of Si wafers in ethanol-hydrogen fluoride solution. This study modifies the components for the electrolyte solution by adding a titanium sol (Ti sol) during electrochemically etching. Ti sol was prepared by mixing tetra-butyl titanate (Ti(OBu)4) with anhydrous ethanol and a little water. An enhancement of photoluminescence from the modified porous silicon has been observed. Fourier transformed infrared (FTIR) spectra showed that antisymmetrical and symmetrical stretching of methylene C-H modes emerges at 2854 and 2928 cm-1 for the modified porous silicon sample. Scanning electron microscopy (SEM) images indicated that there are more detached zones in the modified porous silicon surface than in generally etched porous silicon samples.. X-ray photoelectron spectroscopy (XPS) has detected oxygen, carbon and silicon as the main compositions on the surface of the modified porous silicon. The surface of the porous silicon prepared with Ti sol showed better photoelectrochemical characteristics.3. Photoelectrical Properties of TiO2/PS ElectrodePhotoelectrical Properties of porous silicon (PS) electrode and TiO2/PS electrode were studied. PS was formed by etching n type silicon photo-electrochemically, then the surface of porous silicon was modified by TiO2. Scanning electron microscopy (SEM) images indicated that the surface of TiO2/PS electrode has a layer of uniform TiO2 film. A reduction of photoluminescence from the modified porous silicon has been observed. Fourier transformed infrared (FTIR) spectra showed that the Si-O mode emerges at 1100 cm-1 for the TiO2/PS electrode has clearly reduced because of the existence of Ti. The surface of the porous silicon prepared with Ti sol showed better photoelectrochemical characteristics. Photoelectrochemical effects of the fabricated PS structures were measured by photocurrent-potential relationship. As a result, TiO2/PS electrode showed better photoelectrochemical characteristics. TiO2/PS electrode showed high photocurrent/dark-current ratio and good photoelectrochemical characteristics annealed at 500℃for 1 h.4. Photoelectrical Properties of TiO2/Ag/PS ElectrodeTiO2/Ag/PS electrode was formed by etching n type silicon photo-electrochemically, then the surface of porous silicon was modified by TiO2 and silver nitrate solution. Scanning electron microscopy (SEM) images indicated that the surface of TiO2/Ag/PS electrode clearly has three layer construction. According to theⅠ-Ⅴrelationship and time-current curve, the photocurrent of TiO2/Ag/PS electrode was stabile with the irradiated time, so TiO2/Ag/PS electrode showed good photoelectrochemical stability. However, the heterojunction structure had been destroyed partly, so the photoelectric response of the TiO2/Ag/PS electrode was lower than that of the TiO2/PS electrode. TiO2/Ag/PS electrode showed high photocurrent/dark-current ratio and good photoelectrochemical characteristics annealed at 600℃.