The Optical Properties Of Porous Silicon Microcavity Organic Light-emitting Materials, Mosaic

The discovery of strong visible light emission from porous silicon (PS) at room temperature has opened a door for seeking Si-based integrated optoelectronic devices. However, the photoliiminescence (PL) or electroluminesce (EL) peaks observed from single layer PS film are all broadened bands, which limit the potential application in optoelectronic devices. Porous silicon microcavity (PSM) is an efficient way to improve the emission properties of PS. By employing microcavity techniques, the wide-band emission can be narrowed due to modifying photon mode density. Usually PSMs are realized with P+-type substrates, unfortunately, the external quantum efficiency of PS formed on P+-type doped substrates is very low. In this dissertation, by employing pulsed anodic etching and increasing the viscosity in the electrolyte PSMs with a remarkable optical quality were realized on P-type substrates.Tri (8-hydroxyquinoline) aluminum (Alqs) is one kind of important organic electroluminesence material, but its broad spectrum, spanning the visible range, limits the application such as flat-panel displays. To narrow wide-band emission, in this dissertation, Alqs was embedded in PSMs fabricated by pulsed electrochemical etc-hing. The optical properties of the compound films were studied.In the first chapter, the PL characteristics, structure and formation of PSM were summarized.In the second chapter, experimental set-up and measurement instrument were introduced.The third chapter was about the preparation of PSM aging effects on PSM. Three portions were discussed in this chapter. Firstly, PSMs were prepared by the pulsed electrochemical etching method and the experimental conditions were optimized. Secondly, by employing pulsed anodic etching and increasing theviscosity in the electrolyte PSMs with a remarkable optical quality (FWHM=5nm) were realize with P-type substrates. This characteristic was comparable with that of PSMs realized on P+-type substrates. But the big advantage in this case was the high external quantum efficiency of PS formed on P-type substrates. However, when using ordinary dc etching, a large increase in viscosity caused layer inhomogeneity because of the sticking on the PS surface of the hydrogen gas bubbles evolving during the reaction. Thirdly, aging effects in PSMs were studied, which result in lumine-scence enhancement, resonance peak blue-shift and FWHM increasing. We proposed electrochemical oxidation as a method to control these effects. A signi-ficant suppression of peak shift and FWHM increasing due to aging is achieved.In the fourth chapter, the PL of the PS and PSMs with Alq3 in it was investigated. The PL of the PS embedded Alq3 was similar to that in liquid, but symmetry of the compound film was better and the peak exhibits blue-shift. With the number of molecular of Alq3 increasing, the maximum of the broad emission band exhibited red-shift and the emission intensity was increased; but the intensity was decreased when the conglomeration was too high. To narrow wideband emission Alq3 was embedded into PSMs. The spontaneous emission spectrum of Alq3 was drastically modified by microcavity effect. Compared with luminescence of a filled single PS layer, FWHM of filled PSMs was drastically reduced from 85nm to 15nm and the PL peak emission intensity was increased by a factor of 10. This makes a new way for Alq3 in application in electroluminescence.