Resonant coupling for contactless measurement of carrier lifetime

Abstract

Contactless measurements of the recombination lifetime have become the standard in photovoltaic and electronic materials research, as well as in the associated industries. Fast evaluation is a critical need as well as the need to keep the material under test from becoming contaminated by the measurement apparatus. A technique was developed for measuring the transport properties and recombination kinetics of semiconductors and photoconductors [R. K. Ahrenkiel and S. W. Johnston, Mater. Sci. Eng., B 102, 161172 (2003)]. The primary application of this technique is the measurement of carrier lifetime but carrier mobility can also be linked to the data. The author has named the technique resonance-coupled photoconductive decay and it was developed [R. Ahrenkiel, U.S. patent 5,929,652 (27 July 1999); R. Ahrenkiel and S. Johnston, U.S. patent 6,275,060 (14 August 2001); S. Johnston and R. Ahrenkiel, U.S. patent 6,369,603 (9 April 2002)] at the National Renewable Energy Laboratory. The technique provides the rapid measurement of recombination lifetimes that are of vital importance to electronic and photovoltaic materials. These measurements are also of value to a wide range of optoelectronic technologies. The operating frequencies of the measurements here are in the range of 420 to 430 MHz. The detection is based on the coupling of a high-Q resonant antenna to the sample. The operating frequency is chosen to be in the range of the resonant frequency so that the real and imaginary parts of the system impedance, Z, are changing rapidly. Here, these changes in Z about the resonance produce high sensitivity to changes in carrier concentration produced by photoexcitation.