Easier Way to Detect Damaging Hydrogen in Silicon

Hydrogen can degrade the performance of solar cells, especially those made of silicon. However, these small concentrations of hydrogen are difficult to detect directly.

Hydrogen tends to form pairs with dopants. Simon et al. developed a method to detect boron-hydrogen pairs and measure hydrogen in crystalline silicon at concentrations as low 10¹⁴ cm⁻³.

Direct measurement of the concentration of dopant-hydrogen pairs using infrared absorption spectroscopy is time consuming and must be done at cryogenic temperatures. This new approach uses Fourier-transform infrared spectroscopy (FTIR) to obtain infrared absorption measurements at room temperature and using standard laboratory equipment, meaning it could find use in different silicon technology applications.

“The proposed method can be applied to detect hydrogen in every context of crystalline silicon research and production, since an FTIR setup is rather common in these facilities,” said author Jochen Simon.

While some previous methods to indirectly determine hydrogen concentration in silicon have measured bulk resistivity to quantify dopant-hydrogen pairs, the changes in resistivity were not necessarily due to pair formation. The researchers compared their results to resistivity measurements and found changes in the resistivity of boron-doped silicon samples are caused by the formation of boron-hydrogen pairs.

“The combination of two independent methods on the same sample provides a calibration constant for FTIR measurements at room temperature, which has not been determined in the past,” Simon said.

The authors will apply this method to other doping atoms with which hydrogen pairs, such as phosphorus.

Source: “Quantitative analysis of boron-hydrogen pair dynamics by infrared absorption measurements at room temperature,” by J. Simon, A. Herguth, and G. Hahn, Journal of Applied Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0090965 .