Advanced photoluminescence imaging using non-uniform excitation

Photoluminescence (PL) imaging is a powerful inspection technique for research laboratories and photovoltaic production lines. Common PL imaging systems have two limitations: (a) due to the non-uniformities of the measured samples, the acquired images are affected by lateral carrier flow, resulting in inaccurate lifetime analysis and image blurring; (b) samples' non-uniformities are measured at locally different injection levels. In this paper, we present a PL imaging system that is not affected by these effects. By adaptively adjusting the light intensity at each pixel, we achieve a uniform excess carrier density across the sample, thereby eliminating any lateral currents. The non-uniformity of the minority carrier lifetime can then be extracted from the spatial inverse of the illumination intensity. The advantages of the proposed system are demonstrated using silicon wafers with and without a diffusion layer that contain non-uniform defects. This approach presents a significant improvement in accuracy and sharpness compared to conventional PL imaging techniques and, therefore, is expected to be beneficial for any quantitative PL-based analysis.