Stabilization of electroluminescence and photoluminescence of porous n-silicon by chemical oxidation in H 2 O 2
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677
Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
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EL peak position
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Table 1: typical properties of the samples used in the stabilization experiments. For the oxidation experiments we dipped the porous silicon samples for different times in a solution of 15 % H202 water and ethanol. 2. Influence of H20 2 treatment on the photoluminescence of porous silicon Irradiation of porous silicon with UV light3 leads to degradation of the PL. Also storing the samples in ambient air can deteriorate the PL efficiency of the samples. (This last observation is valid for the bright samples used in these experiments. Porous silicon prepared in the dark from psubstrates usually becomes brighter after storing in air). The PL properties of UV-type and VIStype samples are very similar. So we don't distinguish between the two types in this section. Parallel to the degradation of the luminescence the peakposition shifts to longer wavelengths (Fig. 1). After having processed the sample in a peroxide solution we observe a quite different PL
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exposure time [min] Fig. 2: After immersing a porous silicon sample for 40 min in 15 % H20 2 the PL intensity is stable. The peak position shifts to shorter wavelength during exposure. dependence on the exposure time. Immediately after the process there is only weak PL (see Fig. 2). After an exposure time of about 5-10 minutes, however, the PL intensity exceeds that of the untreated sample. Finally the PL intensity reaches a saturation level which is about 10 % larger than the initial value of the untreated sample. In contrast to the exposure experiment shown in Fig. I the PL peak position shifts to lower wavelengths during the experiment. The processing time of the porous silicon samples in the peroxide solution is essential for the success of the treatment. If the samples are less than 40 minutes in the bath, no stabilization effect can be observed, for longer times the intensity of PL decreases again. 3. Stabilization of electroluminescence In this section we only report results obtained with UV-type samples. The reason for this is that during the chemical oxidation of VIS-type samples cracks in the sample surface appear so that no coherent metal contact can be formed. Untreated porous silic
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