Correlation Between Different Carrier-Lifetime Measurement Methods For Si-Blocks

A reliable material characterization in an early stage of fabrication is essential for further cost reduction in the photovoltaic industry. For the crystalline silicon technology, first investigations can be performed directly after cutting the Si-ingots into blocks (bricks). Thereby, valuable information about the electrical material properties can be gathered from carrier lifetime mappings in the beginning of the production chain. There are several methods available for carrier lifetime measurements for scientific research and industrial process screening. In this work we compare three different methods on Si-blocks of varying material quality quantitatively. The photoluminescence (PL) method has recently been introduced for the characterization of Si-blocks with commercially available measurement tools. It is compared to the widespread micro-wave detected photo conductance decay (μPCD) and the well-established quasi steady state photo conductance (QSSPC) methods. In order to get a better understanding for the interpretation of the measurements various types of silicon are compared. Different materials from standard p-type to compensated silicon are investigated. Within each of these blocks different regions from top to bottom are inspected and the measurement results are evaluated. A spatially resolved co-correlation analysis is used for pixel-wise comparison of the measured data. The results of this work show that in most cases the investigated methods correlate well to each other, i.e. justifying methods for quantitative PL measurements on Si-blocks. However, it is also demonstrated that for some regions within a single block the determined quantities show a rather low co-correlation. The possible reasons for the different response of the methods in certain materials respectively regions within a sample will be discussed.