Variations in the refractive index of the near-surface region of low energy hydrogen ion bombarded silicon

Using ellipsometric analysis, the complex index of refraction of low-energy, hydrogen ion bombarded, (100) single-crystal silicon was measured as a function of distance from the bombarded surface. The bombardment conditions were a 1600 eV hydrogen beam produced by a Kaufman ion source, 1.4 mA/cm/sup 2/ flux, 2 x 10/sup 18/ ions/cm/sup 2/ fluence and 275/sup 0/C bulk silicon temperature. These conditions are comparable to the conditions generally reported to result in a substantial increase in the electrical conductivity of polycrystalline silicon solar cell material. Results indicate that the real and imaginary parts of the refractive index of the ion bombarded surface region approach that of the unbombarded substrate at a depth of 50 nm. The refractive index of about the first 10 nm of ion bombarded material is strongly dependent on the bombardment conditions. Variations in the imaginary part of the refractive index indicate that approximately 10% of incident radiation is absorbed by the first 50 nm of modified material.