Electrical properties of black silicon

Abstract

Black silicon thin films with supersaturated heavily doped sulfur were fabricated on silicon substrates through femtosecond laser scanning the silicon substrate surface in SF6 atmosphere. The temperature characteristics of the carrier concentration and mobility of the two-layer structure, black silicon films/silicon substrate, were measured with variable temperature Hall test methods within the 15-300 K temperature range. Numerical empirical model of carrier mobility and carrier concentration of impurity ionization model were used to fit the temperature characteristics of the carrier concentration and mobility of the two-layer structure, black silicon films/silicon substrate at the same time. The properties of each layer were separated from the measured results. Activation energy E ds was 0.0174 eV, the active sulfur impurity concentration was 3.2903×10 19 cm -3 , the concentration of the substrate doped with phosphorus Ndb was 3.4030×10 14 cm -3 , activation energy of the substrate doped with phosphorus E db was 0.0483 eV.Activation energy of the substrate doped with phosphorus E db and concentration N db were close to the actual measured values，therefore the fitting was effective. Active sulfur concentration in the Black silicon film was very high, and carrier activation energy was very low, so carrier concentration was weakly related with temperature. Carrier mobility was also weakly related with temperature. Black silicon was close to the metal-insulation transition critical point.