Post-Anodization Implantation and CVD Techniques for Passivation of Porous Silicon
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S. P. Duttagupta, L. Tsybeskov, P. M. Fauchet Department of Electrical Engineering, University of Rochester, Rochester NY 14627
E. Ettedgui, Y. Gao Department of Physics and Astronomy, University of Rochester, Rochester NY 14627
ABSTRACT Proper surface passivation is critical for achieving stable, efficient PL from light-emitting porous silicon (LEPSi). As-anodized LEPSi is passivated by hydrogen which desorbs at a temperature as 0 low as 400 °C. For device purposes, it is necessary that porous Si can tolerate at least 450 C for at the that, if the hydrogen established steps. We have annealing/metallization post anodization surface is substituted by oxygen, the resulting Si-Ox passivation is significantly more stable. One way of achieving this is to implant low energy/low dose oxygen to form a thin coating of SiO 2 on
the surface. Post implantation FTIR data report the absence of Si-H peaks. XPS data indicate the formation of nearly stoichiometric SiO 2 at the surface. Similar results were achieved by implanting with nitrogen to form Si 3 N4 . As an alternative to implantation, we have deposited thin capping layers of Si0 2, Si 3 N4 and SiC by plasma-enhanced chemical vapor deposition (PECVD) which resulted in a similar degree of passivation. Wafers were pre-treated at 400 oC to remove hydrogen from the surface. Finally, we carried out a low-pressure CVD (LPCVD) oxide deposition on LEPSi. Post implantation/CVD annealing was done at temperatures up to 600 °C. In most cases, little or no change was observed in the resultant PL intensities.
INTRODUCTION Light-emitting porous Si (LEPSi) is attracting considerable attention since it emits bright visible photoluminescence (PL) at room temperature 1 and thus has significant potential for optoelectronic applications. Unfortunately, it has been observed that the PL degrades following high temperature processing. 2 This is unavoidable in device fabrication where even the final metallization steps typically involve sintering at 450 0C.3 As-anodized LEPSi has a large internal surface 4 of 500 m2 cm- 3 , which is completely passivated by hydrogen. The PL intensity decreases as hydrogen thermally desorbs from the surface, 5 because of the formation of dangling bonds that act as non-radiative recombination centers. 6 It has been reported that oxidation of LEPSi 8 provides a superior passivation. Under anodic oxidation, 7 chemical oxidation or oxidation by light-assisted electrochemical etching 9 stable PL was reported. Rapid-thermal-oxidation of LEPSi10o,1 was shown to result in LEPSi being less susceptible to photo and thermal degradation. However, in many cases a blue shift in the luminescence peak was observed which indicates that
the chemical or physical nature of LEPSi was altered.
In this report we show that passivation of a few surface monolayers can suffice to provide stable PL without affecting the bulk characteristics. In our approach, porous Si was considered to be made of two distinct components, the surface which extends up to only a few monolayers and 381 Mat.
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