"Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium"

Michael Zürch: Hung-Tzu Chang, Lauren J. Borja, Peter M. Kraus, Scott K. Cushing, Andrey Gandman, Christopher J. Kaplan, Myoung Hwan Oh, James S. Prell, David Prendergast, Chaitanya D. Pemmaraju, Daniel M. Neumark & Stephen R. Leone; Nature Communications, 06/01/17.

Additional Authors: Hung-Tzu Chang, Lauren J. Borja, Peter M. Kraus, Scott K. Cushing, Andrey Gandman, Christopher J. Kaplan, Myoung Hwan Oh, James S. Prell, David Prendergast, Chaitanya D. Pemmaraju, Daniel M. Neumark & Stephen R. Leone

Abstract:

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 1020 cm−3. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first-order electron and hole decay of 1 ps suggests a Shockley–Read–Hall recombination mechanism. The simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.