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The surface photovoltage method (SPV method for short) obtains the minority carrier diffusion length by measuring the surface voltage generated by light on the surface of semiconductor materials. The principle is: irradiate the surface of the semiconductor material with monochromatic light with energy greater than the bandgap width of the semiconductor material, and generate electron-hole pairs inside it. The electrons and holes diffused to the near-surface space charge region of the semiconductor material driven by the concentration gradient will be separated by the self-built electric field to form a photogenerated voltage, that is, the surface photovoltage.
The minority carrier diffusion length can be obtained according to the relationship between the surface photovoltage and the photon flux density and wavelength of the incident monochromatic light, the light absorption coefficient of the material, and the minority carrier diffusion length, and then the minority carrier lifetime can be obtained. The SPV method is the main method to characterize the minority carrier diffusion length of semiconductor materials, and its advantages are as follows.
1. A steady-state method that is independent of time, thereby avoiding the influence of in vivo and surface recombination on test results.
2. In general, the surface recombination process does not affect the test results of the minority carrier diffusion length, and the surface recombination rate only affects the surface photovoltage signal intensity, so there is no need for special treatment of the surface of the material.
3. A non-contact test method, which has low test cost, is easy to operate, is not easily disturbed, and can implement surface scanning (mapping).
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