Abstract
AbstractIn this work we describe the controlled shifting of the PL peak of p+ (10 mΩcm) porous silicon (PoSi) by means of atomic layer etching (ALEP). We hereby study the cluster-size dependence of the PL of this material. By this technique of repeated oxidation by H2O2 and stripping of the oxidized surface layer, we reduced the size of the crystallites layer by layer. In all previous reports the PoSi PL appeared to have a natural lower energy limit of ≈ 1.4 eV. We report for the first time a continuous shift of the PoSi PL peak between 1.01 and 1.20 eV. This observation allows us to draw conclusions for the luminescence mechanism: it proves that geometrical quantum confinement in Si crystallites is responsible for the efficient room-temperature PL in PoSi near the indirect bandgap of c-Si. Together with observations of size-independent PL peaks around 1.6 eV in thermally oxidized samples this result indicates that the PoSi PL cannot be described by one origin alone. Both the existence of molecular centers and the geometrical quantum confinement are valid in their specific range of etching and post-anodic treatment parameters.
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