Experimental evidence for luminescence from silicon oxide layers in oxidized porous silicon.

Abstract

A systematic study of the dependence of photoluminescence from porous silicon (PS) on oxidation extent and measurement temperature is given. Oxidation of PS samples at room temperature up to 200 \ifmmode^\circ\else\textdegree\fi{}C results in photoluminescence spectra with maxima centered around 1.7 eV. The photoluminescence maxima shift with temperature 10--300 K always toward the 1.7-eV position. These results conflict with predictions of the quantum confinement model for PS luminescence, but can be explained by assuming that several types of luminescence center outside nanoscale Si units in PS are responsible for the luminescence, and that their relative contributions to luminescence change with oxidation extent and measurement temperature. The luminescence centers with luminescence wavelength around 700 nm in ${\mathrm{SiO}}_{\mathit{x}}$ layers, covering the nanoscale silicon particles or on the interfaces of nanoscale Si/${\mathrm{SiO}}_{\mathit{x}}$ in PS, dominate after sufficient oxidation and their luminescence depends on measurement temperature to a lesser extent than other types of luminescence center do. \textcopyright{} 1996 The American Physical Society.