Visible Electroluminescence from Al-Porous Silicon Reverse Bias Diodes Formed on the Base of Degenerate N-Type Silicon

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Abstract
We demonstrate current induced visible light emission from Schottky junctions between aluminium electrodes and porous silicon formed by electrochemical etching of degenerate n+ -type silicon. HF concentration and anodizing current were chosen to yield preparation conditions in the transition region between electropolishing and porous silicon formation regimes. The light emitting diodes were formed by magnetron sputtering of aluminum on the porous silicon surface. Visible electroluminescence (EL) was recorded when dc or ac voltages larger than 4 V were applied between the aluminium electrodes. The visible EL appears in the dark, at the edge of the electrodes at a reverse bias of 5-6 V. The intensity of emitted light increases with applied voltage; at applied bias higher than 7 V the light emitted was observable by the naked eye at normal daylight. Compared to forward bias solid state contact porous silicon devices, the structure has an increased stability (after 100 hours of continuous operation under a 7 V reverse bias, no appreciable modification was observed in emission intensity). The main features of this electroluminescence are very similar to the ones observed under avalanche breakdown of silicon p-n junctions.

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