V. Pushkarev, T. Ostatnický, H. Němec, T. Chlouba, F. Trojánek, P. Malý, M. Zacharias, S. Gutsch, D. Hiller, and P. Kužel
Quantum-size effects are essential for understanding the terahertz conductivity of semiconductor nanocrystals, particularly at low temperatures. We derived a quantum mechanical expression for the linear terahertz response of nanocrystals; its introduction into an appropriate effective medium model provides a comprehensive microscopic approach for the analysis of terahertz conductivity spectra as a function of frequency, temperature, and excitation fluence. We performed optical pump–terahertz probe experiments in multilayer Si quantum dot networks with various degrees of percolation at 300 and 20 K and with variable pump fluence (initial carrier density) over nearly three orders of magnitude. Our theoretical approach was successfully applied to quantitatively interpret all the measured data within a single model. A careful data analysis made it possible to assess the distribution of sizes of nanocrystals participating to the photoconduction. We show and justify that such conductivity-weighted distribution may differ from the size distribution obtained by standard analysis of transmission electron microscopy images.
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