Optical absorption properties of indium-doped thin crystalline silicon films

The optical absorption of indium-doped thin crystalline silicon films is investigated for photon energies from 1.24 to 2.75 eV (450 to 1000 nm) by transmittance measurements. It is found that the optical absorption coefficient of indium-doped silicon films increases not only in the infrared region but also in the visible region of the spectrum by increasing the concentration of indium impurities below the solid solubility limit of about 1018 cm-3. It is also revealed that this enhancement is more dominant when the sample is thinner than 10 μm. These results imply that In doping is effective in increasing the optical absorption of indirect-band-gap materials such as crystalline silicon.