SURFACE-STRUCTURES AND PHOTOLUMINESCENCE MECHANISMS OF POROUS SI

The position of the valence hand maximum, the Si 2p core level and the SiL(II,III) threshold of porous Si (PS) have been simultaneously measured using a synchrotron radiation photoemission technique. The measured surface optical gap is strongly correlated to the photoluminescence (PL) peak energy, indicating that the surface atomic configuration is related to the PL origin. Freshly prepared PS exhibits a monohydride surface and contains almost no oxygen. The amount of surface oxygen does not correlate with the PL intensity. From these results, it is concluded that oxide compounds including siloxene are excluded from the candidates for the PL origin. Thus, surface oxides of PS act as secondary effects in the PL mechanisms and well-qualified surface oxidation is concluded to lead to efficient electron-hole confinement. Surface energy-band diagrams of freshly prepared PS and partially oxidized PS have been analyzed using the valence, core and total yield spectra. These band diagrams are explained well in terms of band quantization induced by quantum-sized crystallites formed in the surface region of PS.