Novel Free-Carrier Pump/Probe Techniques for the Characterization of Silicon

Abstract

Two novel pump/probe techniques have been developed for measuring the recombination lifetime in crystalline silicon wafers. The first technique, single-beam pump/probe, uses one laser as both pump and probe. The second technique, quasi-steady state free-carrier absorption, measures lifetime under quasi-steady state conditions. These techniques are supported by a general mathematical model that predicts the experimental signal accounting for the 3D charge-carrier transport and recombination within the semiconductor. The predictions of the model are validated experimentally, and quantitative agreement is found between the model and experimental results for both techniques. The recombination lifetime measured by these techniques is verified independently using a standard pump/probe method, and the results are in agreement with this work. Single-beam pump/probe is a first-time demonstration of a technique capable of measuring lifetime in silicon using a single laser beam. It dramatically simplifies traditional pump/probe measurements by completely eliminating the second laser beam. QSS-FCA is the first quasi-steady state technique that can be calibrated in situ without the requirement of a calibrated reference wafer. The calibration constant is the free-carrier absorption cross section of silicon, which is a material constant. QSS-FCA is able to measure this cross section to a higher precision than what has been reported in the literature. Precise measurement of this constant opens up the possibility of studying more fundamental physics of silicon using QSS-FCA.