Design and implementation of transmission-modulated photoconductive decay system for recombination lifetime measurements

Date of Award


Degree Name

M.S. in Electro-Optics


Department of Electro-Optics and Photonics


Advisor: Jay Mathews


Today's problems in silicon photonics will likely require an integration of CMOS compatible, high quality thin films grown on top of Si. GeSn is one of these thin film contenders and is currently being grown on Si platforms. CMOS devices require planar processing and low defect levels in the crystalline structure. A metric that will allow us to quantify defect densities in GeSn is recombination lifetime. Due to their thin film nature and band structure, measuring recombination lifetime in thin films Ge and GeSn can be difficult using industry standard techniques. Thus, we have developed a novel, contactless method in order to measure carrier lifetime called transmission-modulated photoconductive decay (TMPCD). The TMPCD system was first designed and fabricated and then fully characterized with respect to its optical and RF components. The system was validated by measuring lifetimes in bulk Si and bulk Ge. The recombination lifetimes were measured to be 2.6±ł0.5 æs and 7.5±ł0.7 æs for Si and Ge, respectively. These values were found to agree with the values from the literature that were obtained using alternative measurement techniques. Preliminary results so far do not indicate any usable recombination lifetime measurements for GeSn. However, we believe that fine tuning the TMPCD system will allow us to obtain recombination lifetime measurements in GeSn.


Semiconductors Recombination, Nanophotonics, Thin films, Optics, Recombination lifetime, transmission modulated photoconductive decay, silicon photonics, thin films, germanium and germanium tin

Rights Statement

Copyright 2016, author