Improvement of the Luminescing Behaviour of Si + -Implanted SiO 2 Films
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ABSTRACT In previous work we reported on the observation of continuously tunable photoluminescence in Si+-implanted Si0 2-films with moderate intensities. In this paper we demonstrate improved performance of such samples. The photoluminescence intensity increases abruptly up to two orders of magnitude when the anneal temperature is elevated to values higher than 1000... 1100IC. This strong photoluminescence degrades less than that of porous silicon. Very fine tunability in the spectral range from 2.1 eV to 1.3 eV is achieved in samples implanted with a graded dose. In the analysis of the results we try to distinguish between the contributions of the Si-nanocrystals and of the oxide related defects.
INTRODUCTION In the rush of papers dealing with light emitting silicon, where porous silicon is still the object attracting the most attention, more recently another photoluminescing system was introduced, namely Si+-implanted Si0 2 [1-4]. The Sit-implanted Si0 2 represents a very clean, MOS-compatible, quantitatively controllable, compact (absence of pores) system, which offers advantages for applications as well as for better academic understanding of the widely debated problem of the light emission in Si. Generally, the photoluminescence (PL) in the implanted layers is seen to appear after thermal annealing in inert gas atmosphere [1-4]. The Si precipitates in the Si0 2 are considered to be responsible for this behaviour, however the light emitting oxidic defects [5] can not be completely ruled out [1,4]. The formation of Si precipitates in Si0 2 can be understood in the frame of the well known theoretical work of oversaturated solid solutions [6], which was explored previously to understand, for example, the formation of CdS and CdSe in a glassy matrix [7]. In contrast to porous silicon, where the formation of very small Si crystallites is restricted by the fragility of the porous skeleton, very small Si clusters, containing only a couple of Siatoms, can be formed in the implanted layers. As a result of the superior size reduction we observed and reported [4,8,9] superior tunability of the PL in the green/blue spectral region in comparison to porous silicon. However, the quantum efficiency of these samples was moderate in comparison to porous silicon. The decay times are in the nanosecond range for the PL in the green/blue region [9], while the PL decays with microseconds in the red/orange region at room temperature which is also typical for porous silicon [4]. The slow decay time of the PL of Si+-implanted Si0 2 in the red/orange region can not be improved, in principle, for the given luminescence mechanism. In contrast, the quantum efficiency of the PL and its stability can be optimized within a given technological process. We used samples with graded implantation doses to get more detailed information about the dose
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Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
dependent tunability of the PL. Further we increased the annealing temperature to improve the passivation of the surfaces o
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