Wavelength dependent studies of Carrier Resolved Photo Hall measurements
András Bojtor a b, Dávid Krisztián a b, Ferenc Korsós a, Oki Gunawan c, Gábor Paráda a
a Semilab Co. Ltd, 2. Prielle K. str., Budapest, Hungary
b Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Muegyetem rkp. 3, H-1111 Budapest, Hungary
c IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, United States
Poster, Gábor Paráda, 214
Publication date: 6th February 2024

The Carrier Resolved Photo Hall (CRPH) measurement gave a new and interesting technique that allows one to measure the charge carrier mobility, density, diffusion length and recombination time values of majority and minority charge carriers. In the case of photoexcited measurements it is important whether the excitation of charge carriers is homogeneous throughout the depth of the material, the profile of excited charge carriers is determined by the sample thickness and excitation wavelength. The homogeneity of carrier concentration could influence the accuracy of measurements, thus it is a usual criteria for such studies. 

In this study we conducted measurements on Silicon samples using the same measurement parameters while changing the wavelength of continuous wave excitation between 450nm and 637nm. We also made simulations of the excitation wavelength dependent charge carrier distribution in the material to support these results. During these measurements we observed the effect of inhomogeneous excitation in thick silicon samples resulting in inhomogeneous charge carrier distribution. We made additional measurements on the same sample with a microwave photoconductivity decay measurement device and compared the measured charge carrier recombination times. We investigated the possible application of correction methods to compensate for the inhomogeneity in charge carrier distribution and analyzed the accuracy of evaluated charge carrier properties. Despite the inhomogeneous charge carrier distribution during the evaluation process, we were able to extract reliable information using the CRPH method. 

The presented results mean that substantial change in the wavelength of excitation does not change the results obtained during the evaluation process in the case of thick samples in the Hall bar geometry despite the difference in charge carrier generation profile. According to our simulations most solar cell materials of decent quality could be measured with multiple excitation wavelengths. By measuring materials with two excitation wavelengths and comparing the results we can obtain information about the accuracy of the evaluation and the quality of the analysed sample. 

Despite the presented measurement being conducted on a silicon sample the method and the information these results yield are applicable to any photovoltaic material. 

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