Light-induced degradation on porous silicon

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Abstract
A study of photoluminescence degradation profiles in porous silicon as a function of time, temperature, and excitation intensity is reported. It is found that the degradation of the photoluminescence follows a stretched exponential function with the stretching parameter and the relaxation-time constant independent of the measured temperatures. The intensity of the saturated photoluminescence is linearly proportional to the excitation intensity, which indicates that the number of saturated nonradiative recombination centers does not depend on the excitation intensity. These results can be understood on the basis of the following mechanism: the defects in porous silicon are distributed exponentially in energy, and energy liberated upon carrier capture by the defects is localized in the vicinity of the defect and can be utilized to promote defect reactions and create nonradiative recombination centers. In addition, the striking results of the slowdown of the degradation rate and the enhancement of the photoluminescence intensity by illumination with an additional He-Ne laser can also be explained using the same mechanism.