Ultrasound treatment for porous silicon photoluminescence enhancement

One of the most important properties of the porous silicon is its strong visible photoluminescence. However the intensity and the shape of the photoluminescence is changing as the sample ages, due to absorption of oxygen and hydrogen in the skeleton of the porous layer. This is why a good passivation for the porous silicon is crucial in order to fabricate a stable and reliable device with well-defined characteristics. Porous silicon was exposed to an ultrasonic treatment in order to increase the photoluminescence intensity and to passivate the layer. In this work we show that the ultrasound treatment increases the photoluminescence intensity by a factor of 2-3 in a very short period of time (10 min). Long ultrasound treatment results in a smaller increase of the photoluminescence intensity but dramatically slows the aging process of the porous silicon. We believe that the ultrasonic treatment introduces some energy to the porous silicon, allowing the traps in the skeleton to be repopulated. In this process, the deeper traps get occupied while the shallower traps are kept free, allowing the photoluminescence to increase and the aging process to decay.