Study On Forming Mechanism And Photoluminescence Properties In Porous Silicon

The study of low dimension semiconductor is a very active field of research and has important technical applied promise. Simply prepared method, complex constructure characteristics and higher photoluminescence efficiency in porous silicon have attracted a lot of attention of investigators. Since Canham detected that porous silicon can emit visible light at room temperature in 1990, a lot of significative work have been done on its formation and radiation mechanism and the possibility of technical applied. Beale model, diffusion confinement model and quantum confinement effect model are used to explain how porous silicon comes into being. Many experimental results reveal that a great deal of nanocrystal silicon particles and cylinders with certain size distribution in porous silicon has complex constructure and hold the character of monocrystaline silicon, in which nanosilicon is order monocrystaline. Hydrogen, fluorin, carbon and oxygen are familiar elements in PS confirmed by different experiments. Porous silicon can radiate strong near infrared, visible and near ultraviolet light, but whole S band is most interested in. PS radiation mechanism has been discussed and investigated for many years and many theoretical models have been proposed to describe photoluminescence in porous silicon, for instance quantum confinement effect model, polysilanes model, siloxen and its derivant, surfacial states model and quantum confinement-light center model etc. In addition, study status of PS at present is addressed and applied problems in some fields are analyzed in this section.On the experimental side, research suggests that microstructure of PS (porosity, film thickness, aperture etc.) and its radiative properties are determined by prepared technics and conditions, so it is fundamentalapproach that investigate prepared method and conditions to promote the development of PS applied. At first, we prepared PS samples at room temperature by electrochemical method, photochemical method and pure chemical method and measured its PL spectrum separately. By compared setup, conditions, formed process and their PL spectra, their formed mechanism and PL spectrum characteristics are analyzed and explained. These three methods all can prepare PS, which radiate visible light at room temperature, but samples prepared by electrochemical method is uniformity relatively and the experiment has more repeatability, so it is extensively applied to prepare PS. Otherwise, free carriers play an important role in the process of film forming.Many experimental results and theoretical analysis diverge mostly because different conditions can seriously affect PL properties in porous silicon. In the third chapter, the influence of current density, solution concentration, erosion time and aging in ambient air on the PL spectra of PS suggests that peak would blue shift with current density increasing, and with erosion time and aging time prolonging; With the increasing of solution concentration, peaks would red shift when solution concentration less than 1:1 but blue shift when solution concentration greater than 1:1. Above phenomena can be explained by quantum confinement and light center model, but do not deny the action of Si-H bonding and defect on the surface in the process of photoluminescence.At present, radiation mechanism is still one of the primary problems in the study of PS. With the development of study and various measurement techniques, Si as major material in microelectronics field shows wide promise in photoelectronics field.