Photoluminescence Study Of Porous Silicon By Double Cell Anodic Electrochemical Etching

The microstructure (porosity, pore size, thickness, ect) and their luminescence properties of porous silicon are depended on their preparation methods and preparation conditions. So, the study of porous silicon preparation methods and preparation conditions is a basic ways to implement application.In this thesis, PS was obtained by anodic electrochemical etching. The dependence of visible photoluminescence(PL) of porous silicon and its microstructure on the anodization conditions(current density, etching time, and solution concentration) and after-treatments(cathodic reduction treatment, acid treatment, and cathodic reduction-acid treatment) were studied systematically. With Photoluminescence(PL) measure we analyzed those conditions effects on luminance of porous silicon. By means of Screen Electronic Microscope (SEM) we discussed the samples surface look and components.Experimental results indicated:(1) The effect of electrochemical anodization was on the microstructure and photoluminescence(PL) of porous silicon. The results showed:1) The increase of etching time and current density resulted in a blue shift of luminescence wavelength of porous silicon, photoluminescence intensity increased at the first, and then decreased.2) Concentration on the luminescence properties of porous silicon was more complex. With the increase of concentration, luminescence intensity increased, and then decreased. At the same time, luminescence peaks "red shift" and "blue shift" were existed. When HF concentration was small (<20%), luminescence peak was toward to low-energy with concentration'increase, "red shift"; when HF concentration was higher than 20%, luminescence peak was shifted to high-energy, "blue shift". Considering all the results, we got the optimized conditions of preparation porous silicon by electrochemical anodization:current density 50mA/cm2,time 45min, concentration V(Φ=40% HF-H2O):V(C2H5OH)=1:1. On other types of silicon chip, these conditions may not optimal. (2) In this paper, we have discussed the effects on luminance stability through different treatments to porous silicon. We adopted anodic etching to make porous silicon samples under different optimal conditions, after that, we treated those samples through cathodic reduction, acid treatment and cathodic reduction-acid treatment respectively in order to improve the samples'surface. Experiment results showed that the luminance efficiency of porous silicon was improved by cathodic treatment and acid treatment, and cathodic reduction-acid treatment was a useful treatment to improve luminance efficiency, which showed "blue shift" in luminance peaks, we also discussed its mechanism. We studied the luminance stability of porous silicon samples mainly untreated and by cathodic reduction-acid treatment in this paper. With excitation times'increase, PL intensity of porous silicon without treatment decayed exponentially, and finally stabilized; PL intensity with acid treatment decayed exponentially rapidly in lmin, and then increased slowly. We also discussed its action mechanism of porous silicon, and showed specific reasons in further study.