On the origin of the 2.2–2.3 eV photoluminescence from chemically etched germanium

The photoluminescence (PL) at ∼2.2–2.3 eV from Ge-based nanocrystalline materials is described in the literature as nanocrystal size-independent. We have observed visible luminescence from two different types of stain-etched Ge samples, one prepared after Sendova-Vassileva et al. (Thin Solid Films 255 (1995) 282) in a solution of H2O2:HF at 50:1 volume ratio, and the other in a solution of HF:H3PO4:H2O2 at 34:17:1 volume ratio. Energy dispersive X-ray analysis (EDX), Raman and FTIR spectroscopy, and the near edge X-ray absorption structure (XANES), indicate that the chemically etched Ge layers of the former type of samples are composed of non-stoichometric Ge oxides, i.e. GeOx (0