CHANGES IN LUMINESCENCE PROPERTIES OF POR OUS SILICON LAYER DUE TO ANODIC-OXIDATION

A porous silicon layer (PSL) was prepared on p-type single crystal Si (100) wafer with sin electrochemical etching in ethanol solution of 12 .6 wt% HF. An anodic oxidation of PSL until 500 V (SHE) in 0.1 M KNO3 ethylene glycol solution was performed to improve visible photolumines cence (PL) properties of PSL. Moreover, an electroluminescence (EL)emi tted from PSL during anodic oxidation was measured to understand anodi c oxidation mechanism of PSL. The TEM image and FTIR spectra have indi cated that PSL as prepared consists of Si nanoparticles with a diamete r of 2 nm - 5 nm and the Si nanoparticles are covered with silicon hyd rides, SiHx. At the initial stage of anodic oxidation of PSL where the potential remains a low value, silicon hydrides on Si nanoparticles a re firstly oxidized to elemental Si and simultaneously an EL with a pe ak wavelength of 800 - 710 nm is emitted from the PSL. In the subseque nt oxidation region where the potential rises linearly with time, Si n anoparticles are oxidized to SiO2 and simultaneously an EL with two pe ak wavelength of 650 and 530 nm is emitted from the PSL. The origins o f these EL emission sources were explained by using an electronic band model of Si/SiHx/solution interfaces or Si/SiO2/solution interfaces T he PL spectra of PSL as prepared have a peak wavelength of 660 nm. The PL intensity increases and the PL spectra shifts toward short wavelen gth as anodic oxidation of PSL proceeds. It has been discussed by usin g the electronic band model that the decrease in surface state density of Si nanoparticles due to anodic oxidation would enhance significant ly the PL intensity, The above results support that the quantum confin ement effect is operative in the visible PL of PSL subjected to anodic oxidation.