Temperature-dependent Photoluminescence Imaging using Non-uniform Excitation

Photoluminescence (PL) imaging is a powerful inspection technique for research laboratories and production lines. It is used for a wide range of applications across the entire manufacturing chain from bricks and ingots to modules. However, common PL imaging systems have three main limitations: (a) Due to the uniform illumination, the acquired images are affected by lateral carrier flow, resulting in image blurring; (b) sample's non-uniformity is measured at different injection levels; and (c) images are taken at room temperatures, although there is valuable information in temperature-dependent measurements. In this paper we present a novel temperature-dependent PL imaging system that is not affected by lateral balancing currents. By adaptively adjusting the light intensity at each pixel, we set a uniform excess carrier density across the sample. Hence, the lateral currents are eliminated. The non-uniformity of the material's electrical properties and temperature characteristics can then be extracted from the excitation image. The advantages of the proposed system are demonstrated using mono and multi-crystalline silicon wafers. This novel approach presents a significant improvement in accuracy and resolution compared to conventional PL imaging techniques and is therefore, expected to be beneficial for any PL-based quantitative analysis.