Properties of green-light-emitting anodic layers formed on Si substrates in HF/MnO2 mixed solution

We report the properties of anodic layers formed on p-Si substrates in a 50% HF solution with the addition of an oxidizing agent MnO2. The structural and optical properties are investigated using scanning electron microscopy (SEM), photoluminescence (PL), PL excitation, x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The anodic layers formed have several unique properties. For example, they are stable in acidic solutions, HF, HCl, and CH3COOH, regardless of light illumination but are unstable in air exposure or in water regardless of light illumination and in methanol under UV illumination. The as-prepared layer emits light in the green spectral region, but an exposure in air without light illumination or in methanol with UV illumination leads to spectral redshift with increasing its intensity. The SEM image indicates that the anodic layer usually shows a double-layered (much roughened top/uniform bottom) structure. The XPS and FTIR spectroscopy support that the anodic layer is any compound of the hydroxyl group or others. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3142425]