Photoabsorption Cross Section for Silicon Doped with Indium

The photo-ionization cross section for indium as an acceptor in a silicon lattice has been deduced from optical transmission coupled with wide-range Hall-effect measurements. The normalized energy dependence observed in our samples agrees well with results previously reported, but the cross section we report has a maximum value of σₘₐₓ=3.3×10^-17 cm² at hν=0.3 eV. This is several times smaller than has traditionally been believed. The effective field ratio necessary to fit our data with a quantum-defect model agrees well with the local field predicted for a cavity in a dielectric medium. The general form of the energy dependence of the cross section accords with a quantum-defect model, but we do find that the behavior for energies above 0.4 eV is dependent on the doping and degree of compensation in the crystal.