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Improved Contactless Method of IR Reflectance under Grazing Incidence for Measurement of Doping Profiles
J. Holovsky, Z. Remes, D. Franta, B. Conrad, L. Abelová, D. Bušek, A. Poruba
Diffusion, Characterisation, Characterization, Free-Carrier Absorption, In-Line, IR Spectroscopy
Silicon Cells
Subtopic: Characterisation & Simulation Methods for Si Cells
Event: 35th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2AO.5.3
278 - 280
ISBN: 3-936338-50-7
Paper DOI: 10.4229/35thEUPVSEC20182018-2AO.5.3
0,00 EUR
Document(s): paper


We have elaborated contactless method of measurement and evaluation of doping profiles in silicon polished wafers based on infrared reflectance under high angle of incidence. We have found higher angle of incidence increases sensitivity, however approaching Brewster angle increases also experimental error, therefore 65 angle has been chosen. Moreover, to increase reproducibility we divide the measured spectra by reference spectra taken on an undoped sample, and further we rescale the spectra to fixed value in the region of 4000 cm-1–7000 cm-1. To reduce number of evaluated parameter, the carrier profile in boron-doped samples was parametrized by 3 parameters and that in phosphorous-doped samples was parametrized by 4 parameters, using additional empirically determined assumption that the first part of the profile is a constant plateau and that the following two exponential tails are joined at a value of 3x1019 cm-3. As a physical model, the classical Drude equation is used and revised, leading to adjustment of effective mass and assuming concentration-dependent relaxation time and the contribution from band-to-band excitations. The relation of concentration-dependent relaxation time was represented in the range of interest by a power law that significantly deviates from typically used empirical data. The reason is that the empirical data had been obtained as a function of dopant density and not free carrier density. Because the doping efficiency drops at higher concentration this empirical data could not be used. This is one of the most important advancement of the free carrier absorption model. Finally, the model parameters were calibrated independently by infrared ellipsometry. Satisfactory agreement with the profiles measured by the electrochemical capacitance-voltage method was reached. The measurement using Fouriertransform infrared spectrophotometer takes few seconds and can be implemented as an in-line characterization technique in industry.