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

Abstract

We present a camera-based technique for the local determination of reverse saturation current densities J 0 of highly doped regions in silicon wafers utilizing photoconductancecalibrated photoluminescence (PL) imaging at different illumination intensities. We apply this approach to 12.5 × 12.5 cm 2 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 ,m eta llized = 1000 fA/cm 2 for the metalized areas compared with the nonmetallized area characterized by J 0 ,n o n m eta llized = 330 fA/cm 2 .

Dynamic Infrared Lifetime Mapping for the Measurement of the Saturation Current Density of Highly Doped Regions in Silicon

“…The front reflectivity R front of the sample at the excitation wavelength λ exc = 930 nm follows from reflectance measurements using an integrating sphere. Finally, the images of J 0,rear + J 0,front are determined from the local τ eval and Δn eval according to (1).…”

“…To determine J 0 , we measure the lifetime of lowly doped Si samples under high injection conditions (Δn N A ) according to (1). Under such conditions τ eff depends strongly on the excess charge carrier concentration Δn [18].…”

“…for the case of injection-dependent lifetimes τ eff (Δn) according to (1). The modulated photon flux Φ(t) is considered as time dependent.…”

“…For this purpose, we consider an injection-dependent lifetime according to (1). We calculate for this lifetime the evaluated lifetime τ eval using the numerical simulation according to (3).…”

“…This geometry makes it particularly attractive to employ an imaging method to determine J 0 locally. Recently, Müller et al [1] introduced a J 0 imaging method based on photoconductance-calibrated photoluminescence imaging [2] under high-level injection. This technique has been applied Manuscript to study recombination properties of laser processed selective emitter structures [3].…”