SPECTROSCOPIC INVESTIGATION OF ELECTROLUMINESCENT POROUS SILICON

Light-emitting porous silicon films have been obtained by anodic etchi ng p-type Si samples in a HF-ethanol solution. Porous Si samples effic iently luminesce at room temperature in the visible region. A degradat ion of the luminescence intensity with time is observed. Micro-Raman s pectroscopy of free-standing porous silicon layers indicates phonon co nfinements as well as a strong laser heating effects. The surface chem ical composition and the effect of electron-beam irradiation has been investigated through Auger spectroscopy. The Si LVV Auger transition d ominates the spectrum, even in aged samples. The Si line shape gives e vidence of a covalent bond between the porous Si surface atoms and som e adsorbed species. A prolonged electron irradiation results in a stro ng variation of the surface chemical composition, with an anomalous ca rbon accumulation. Gold thin films have been deposited on the porous S i surface to form metal-semiconductor junctions. Schottky diodes with large rectifying ratio, ideality factor, and series resistance are obt ained. When the junction is forward biased, electroluminescence is obs erved. Electroluminescence degrades with time while the current does n ot. When the junction is reverse biased a significant photocurrent is obtained. The results are discussed in the framework of the surface st ate emission model for the luminescence.