Determination of complex dielectric functions of ion implanted and implanted-annealed amorphous silicon by spectroscopic ellipsometry

Abstract

Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ε = ε1 + iε2) of different kinds of amorphous silicon prepared by self-implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a-Si (i-a-Si) differs from that of relaxed (annealed) a-Si (r-a-Si). Moreover, its ε differs from the ε of evaporated a-Si (e-a-Si) found in the handbooks as ε for a-Si. If we use this ε to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ε2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i-a-Si), 1.12 eV (e-a-Si), 1.30 eV (r-a-Si). We attribute the optical change to annihilation of point defects.