OBSERVATION OF OPTICAL CAVITY MODES IN PHOTOLUMINESCENT POROUS SILICON FILMS

Uniform layers of porous Si have been produced that show fine structure in their photoluminescence (PL) spectra characteristic of longitudinal optical cavity modes. This mode spacing can be modified in a predictable way by immersing the porous Si layer in heptane, which changes the average refractive index of the porous Si layer. The 5 mu m thick cavity is generated by a photoelectrochemical etch of single-crystal (100) p-Si wafers (3 mA/cm(2), 9 C/cm(2), irradiated with 57 mu W/cm(2) of 500 nm light for the duration of the etch). Electron micrographs show that the layer is homogeneous on a submicron scale and that the Si/porous Si and porous Si/air transitions are abrupt (<0.5 mu m). On thinner porous Si films, optical interference leads to a significant distortion of the emission spectrum. The relevance of interference-induced spectral changes to measurements of the intrinsic emission spectrum of porous Si is discussed.