Strongly Reduced Si Surface Recombination by Charge Injection during Etching in Diluted HF HNO3

In this study, we investigated the behaviour of the surface recombination of light induced charge carriers during the etching of Si in alkaline KOH and in acidic etching solutions of HF HNO3 CH3COOH HNA or HF HNO3 H3PO4 HNP at different concentration ratios of HF and HNO3 by means of photoluminescence PL measurements. The surface recombination velocity is strongly reduced during the first stages of etching in HF HNO3 containing solutions pointing to a well passivated interface by the etching process, where a positive surface charge is induced by hole injection from NO related surface species into the Si near surface region back surface field effect . This injected charge leads to a change in band bending by about 150 mV that repulses the light induced charge carriers from the surface and therefore enhances the photoluminescence intensity, since non radiative surface recombination is reduce