Quantitative analysis of boron–hydrogen pair dynamics by infrared absorption measurements at room temperature

Abstract

The ability of hydrogen quantification in crystalline silicon in concentrations as low as 1014cm−3 becomes fairly important in regard to hydrogen-related degradation phenomena in silicon devices generally and solar cells particularly. The method presented here allows for direct boron–hydrogen pair quantification and, therefore, allows inference on total hydrogen content. Hydrogen-rich amorphous silicon nitride was deposited on stripes of boron-doped float-zone silicon (1 Ωcm), which were exposed to a rapid high temperature step to introduce relatively high amounts of hydrogen into the wafer. Infrared absorption spectra, which have been corrected for multiple reflection and free-carrier absorption, show absorption related to the boron–hydrogen stretching mode at ν~=1868cm−1 with varying strengths during formation and subsequent dissociation of boron–hydrogen pairs triggered by annealing in the dark at 220°C. Since the measurements were performed at room temperature, this method allows investigations with little effort and standard laboratory equipment. Furthermore, the change in free-carrier absorption (described by Drude’s theory) is used to derive the change in hole concentration concurring with the formation and dissociation of boron–hydrogen pairs. The latter is found to fairly match not only the changing strength in absorption of the stretching mode, but also the change in hole concentration obtained by highly sensitive resistivity measurements. The comparison of stretching mode absorption strength and change in resistivity allows for a calibration of specific absorption, yielding a calibration factor ABH. This calibration was performed with the absorption α [ABHα=(4.2±0.3)×1015cm−1] as well as with the quotient of absorption and wavenumber α/ν~ [ABHα/ν~=(7.8±0.6)×1018cm−2].