Passivation of Si Surfaces Investigated by In Situ Photoluminescence Techniques

Abstract

We investigated Si surfaces modified by wet-chemical and electrochemical treatments using pulsed photoluminescence (PL) and infrared spectroscopic ellipsometry during and after processing, both also in surface mapping techniques. Etching of oxidized Si surfaces by HF containing solutions lead to an enhancement in PL due to hydrogenation of the surface what improves the surface passivation and reduces the recombination loss of charge carriers via surface/interface states. PL measurements show that the H-terminated surface is attacked soon by HF or H2O species increasing again the recombination loss. Hence, a narrow time window for this type of processing exists. Nitrogen purging or exchanging the etching solution by a non-etching solution under negative bias decelerated the defect formation in HF solutions. Grafting of organic molecules (exchanging the H-Si by a C-Si bond) induces only small amounts of defects at the interface but stabilizes PL on a high level (i.e. surface recombination is low) for much longer times than for H-terminated Si surfaces.