Electroluminescence and photovoltaic effects of anodically fabricated metal/porous Si/Si sandwich structures based on ntype ultravioletporous Si

The use of silicon based light emitting diodes may completely solve the problem of low compatibility of optoelectronics elements and silicon chip. At present time the most suitable kinds of Si-LEDs are monocrystal and porous silicon avalanche LEDs. They have advantages such as long operation lifetime (> 10000 hours), continuous spectrum, which allows to filter RGB colors, operation voltages (< 12 V), extremely sharp voltage-current characteristic, nanosecond response time, and high high operation current densities (up to 8000 A/cm 2 in pulse mode). Rather low energy efficiency (< 1%) is not so significant for near to eyes (NTE) microdisplays. These advantages open a way to design a high performance and cost effective passive addressed microdisplays.

We report the realization of a bright and stable electroluminescent Schottky diode based on aluminum-porous silicon junction. White light, visible in normal daylight, is emitted when a reverse bias is applied to the device, promoting the junction breakdown. The device has a fast (100 ns) rise time of the light emission. An excellent stability, tested over more than one month of continuous operation at a high bias level, is achieved by the complete encapsulation of the active porous silicon under a transparent alumina layer. The external power efficiency of light emission is 0.01%.

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The fabrication technologies and the properties of light-emitting devices based on A 1-porous silicon (PS) Schottky junctions have been developed. Bright light emission, visible by the naked eye at normal daylight, is observed at the edge of the electrodes under reverse bias.The electroluminescence (EL) starting voltage is in the range 5-18 V, depending on the doping level of Si substrate. The current level at which the EL starts is around 1 mA for devices of 2.3 X 10 " 3 cm 2 area. The lighi emission intensity increases with increasing current density. EL spectra were broad, covering the whole visible range.The time stability was excellent for all tested devices; the EL intensity did not show remarkable changes, even after more than ten days of continuous light emission at voltages lower than thermal breakdown.

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