The effect of etching temperature on the photoluminescence emitted from, and the morphology of, p-type porous silicon

The temperature at which silicon is electrochemically etched has been found to influence the structure and photoluminescence properties of porous silicon. Decreasing the temperature increased both the current efficiency of the dissolution process and the porosity of the resulting porous layer. Furthermore, a blue-shift was observed in the photoluminescence indicating that the decreased temperature allowed smaller nanocrystals to be formed. An analysis of temperature dependence of the pore initiation and propagation models currently available in the literature failed to yield a satisfactory explanation for the decrease in the average size of the nanocrystals indicated by the results presented in the present paper. Therefore it was proposed that at lower temperature smaller nanocrystals are stabilized due to a combination of their reduced solubility and the increased viscosity of the diffusion layer that leads to a higher localized concentration of silicon ions, thereby allowing smaller nanocrystals to be in equilibrium with their surroundings. The fact that previous authors did not observe blue-shifting highlights the importance of the composition of the etching solution in controlling the quality of the porous silicon produced.