Temperature-dependent Photoluminescence Imaging using Non-uniform Excitation

Abstract

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 nonuniformity 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 multicrystalline 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.