Reverse Saturation Current Density Imaging of Highly Doped Regions in Silicon Employing Photoluminescence Measurements

We present a camera-based technique for the local determination of reverse saturation current densities J₀ of highly doped regions in silicon wafers utilizing photoconductance-calibrated photoluminescence (PL) imaging at different illumination intensities. We apply this approach to 12.5 × 12.5 cm² float zone silicon (Si) samples with textured surfaces and a homogeneous phosphorous diffusion with sheet resistances between 24 and 230 Ω/□. We find enhanced PL emission at metallized regions of a sample due to reflection of long-wavelength light at the sample rear. In order to allow for a transfer of the calibration function relating the camera PL signal to the excess charge carrier density Δn, our measurement setup comprises an optical short-pass filter in front of the camera that effectively blocks wavelengths above 970 nm. Investigating samples comprising local metal contacts to the highly doped regions prepared by screen printing of silver paste, we find a significantly higher J_0,metallized = 1000 fA/cm² for the metalized areas compared with the nonmetallized area characterized by J_{0,nonmetallized} = 330 fA/cm².