No Correlation Between Porous Silicon Photoluminescence and Surface Hydrogen Species

The photoluminescence (PL) of porous silicon has been attributed to quantum confinement, amorphous silicon, or surface species such as hydrogen, polysilanes or siloxene. Our research has tested the early claims that surface hydrogen is responsible for PL. Our initial studies examined the effect of thermal annealing on surface hydrogen and PL in situ in an ultrahigh vacuum chamber. The results showed that the PL decreased between 450–550 whereas H2 was desorbed from surface SiH2 species between 500–575 K. There was no direct correlation between the PL and the loss of SiH2 surface species. Our most recent investigations have monitored PL and surface hydrogen species as a function of HF etching time for electrochemically anodized porous silicon samples that were not initially photoluminescent. While the surface hydrogen species continually decreased versus HF etching time, the photoluminescence did not appear until after HF etching times of 20–80 minutes depending on initial sample porosity. These results again illustrated that there is no direct correlation between the PL and surface hydrogen species.