Preparation of H-terminated Si surfaces and their characterisation by measuring the surface state density

H-terminated n- and p-type Si(111) surfaces are characterised by the large-signal field-modulated photovoltage technique (SPV) measuring the surface potential and the energetic distribution of surface states Dit(E). Using aqueous HF acid (HF) and buffered HF solution (BHF), different methods of chemical preparation were carried out characterising the treated surfaces repeatedly during the preparation process. The ideal H-terminated surface displays a very low density of surface states, comparable to well thermally oxidised surface and a significant decrease of HF-induced positive surface charge. The absence of these extrinsic defects indicates the successful preparation of H-terminated surfaces characterised by a nearly intrinsic surface state distribution. The surface state density was found to be mainly influenced by three aspects of the preparation: the doping type and the surface morphology of the substrate, the kind of chemical treatment, and the clean-room conditions as well. Very low surface state density (5 × 1010 cm−2 eV−1 and about 2 × 1010 cm−2 eV−1 on n-type and p-type Si surfaces, respectively) were obtained using BHF as final etching solution, when the treatment was carried out in N2 atmosphere.