OXYGEN-ASSOCIATED DEFECTS NEAR SI-SIO2 INTERFACES IN POROUS SI AND THEIR ROLE IN PHOTOLUMINESCENCE

Porous is comprised of nanometer-scale crystallites of Si which, on ex posure to the atmosphere, become surrounded by thin oxide layers. It h as been proposed that the red room temperature luminescence in this ma terial is primarily due to defects at or near the interface between th e crystallites and the thin oxide. We report here the observation of t wo electron spin resonance (ESR) active oxygen-centric defects; one in nominally unoxidized porous Si and the second in material which has b een oxidized for a short period of time. The first is a variant of the thermal donors observed in crystalline Si and the second is the EX ce nter observed in thin layers of SiO2 on crystalline Si. These two cent ers are thought to have similar cores, a Si vacancy surrounded by four Si-O linkages, with the primary difference in the surrounding lattice (Si vs SiO2). The ESR intensity of the EX center is related to the ph otoluminescence intensity and may be directly involved in the luminesc ence process.