Post-Anodization Implantation and CVD Techniques for Passivation of Porous Silicon

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 low as 400 °C. For device purposes, it is necessary that porous Si can tolerate at least 450 °C for post anodization annealing/metallization steps. We have established that, if the hydrogen at the surface is substituted by oxygen, the resulting Si-O_x passivation is significantly more stable. One way of achieving this is to implant low energy/low dose oxygen to form a thin coating of SiO₂ on the surface. Post implantation FTIR data report the absence of Si-H peaks. XPS data indicate the formation of nearly stoichiometric SiO₂ at the surface. Similar results were achieved by implanting with nitrogen to form Si₃N₄. As an alternative to implantation, we have deposited thin capping layers of SiO₂, Si₃N₄ and SiC by plasma-enhanced chemical vapor deposition (PECVD) which resulted in a similar degree of passivation. Wafers were pre-treated at 400 °C 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.