ProPerties Of Photolumlnescence In Porous Silicon

The development of semiconductor photo-electronics has been dominated by III-V compound semiconductors such as GaAs and InP which are good at emitting light but are more expensive than silicon and are hard to integrate into silicon microchips, primarily due to the direct energy band gap available in many important III-V materials. In contrast, the development of Si-based photo-electronics has been severely limited by the fundamental band-structure limitation: a small and indirect band gap of 1.1 eV at room temperature. The observation of visible-light emission from porous Si has begun to revitalize silicon's role as a material for optical electronics. The discovery that porous silicon (PS) can emit visible light at room temperature has aroused great interests because of its potential applications in the areas of optoelectronics and display system. However, the luminescence mechanism of PS is still a controversial problem.Electrochemical anodization method is the typical approach for preparing uniformly PS, which show intense PL in the visible wavelength region. The PS structure can be fabricated by simply anodizing bulk Si in an HF-based solution. The approach used in this paper is two-cell approach. Based on the applications in the future, this paper has in detail studied the formation mechanism, photoluminescence (PL) and temperature dependence of PL in porous silicon. After having summarized previous studies in chapter one, we present the research results for formation process and PL of PS in chapter two. The PS morphology and its optical properties strongly depend on the anodization parameters, such as anodization time, HF concentration,anodization current density, and illumination condition etc. the formation mechanisms of porous silicon are discussed at the same time. We believe porous silicon made of n-Si has different formation mechanism from that of p-Si.The temperature dependence measurement of the PL is generally considered as an important method to reveal the luminescence mechanism of PS. The property of PL from PS has been investigated in chapter three. It is found that the peaks from the high porosity samples show a red shift with increasing temperature, the peaks from the low porosity ones show a blue shift, others with moderate porosity are independent of temperature. And the emission intensity increases with decreasing temperature until reaching an intensity maximum at the intermediate temperature, and then decreases at lower temperature. Many experimental results which conflict with predictions of the quantum confinement model for PS luminescence have been analyzed at the same time. The SiOx layer covering the nanoscale silicon is believed to play an important role in PL of PS. PS has at least two kinds of different PL spectra in the nanoscale silicon and the SiOx layer. The reason why PL in PS is dependent upon temperature is that relative contributions to PL of the two PL spectra change with temperature. Finally, a new model based on quantum confinement effect is put forward to account for experimental facts as stated above.In chapter four this paper presents problems and expectation of porous silicon's application in some fields in the future.