Strong confinement-induced nonlinear terahertz response in semiconductor nanostructures revealed by Monte Carlo calculations

Challenging Kubo-Greenwood Theory: Nonunitarian Dynamics Reshapes THz Conductivity and Transport in Nanosystems

“…In recent years, more and more applications of semiconductor nanomaterials with quasi-continuous excitation evolve, e.g., in solar energy harvesting or hydrogen generation. , On the other hand, nanophotonics and nanoelectronics − develop to higher frequencies, e.g., for direct detection at THz frequencies or THz time domain imaging, so that understanding charge carrier and exciton transport in all frequency regimes becomes crucial for applications. THz time domain spectroscopy − is a powerful tool to study charge mobility and exciton polarizability in quantum dots, quantum wires, and quantum wells. − Models, like Drude ,, or Drude-Smith, − have been used to fit the frequency dependence, the latter including backscattering terms at domain boundaries. However, they deliver only limited insights into the basis of the observed transport properties.…”

“…THz time domain spectroscopy 9−11 is a powerful tool to study charge mobility and exciton polarizability in quantum dots, quantum wires, and quantum wells. 12−20 Models, like Drude 10,21,22 or Drude-Smith, 23−25 have been used to fit the frequency dependence, the latter including backscattering terms at domain boundaries. However, they deliver only limited insights into the basis of the observed transport properties.…”

Field-dependent THz transport nonlinearities in semiconductor nano structures

“…Although there is indepth understanding of linear transport in bulk and nano semiconductors based on Drude, Drude-Smith and Kubo-Greenwood based models, [26][27][28][29][30][31][32] understanding of nonlinear transport and charge carrier mobility remains scarce. [33][34][35][36] Recent density matrix calculations show strong THz transport nonlinearity in nanowires as well as a yet unexplored equilibration current, suppressing the low-frequency charge (or exciton) mobility. 32,34,37,38 The latter can be understood in the frame of a generalized Kubo-Greenwood theory including charge carrier relaxation and dephasing.…”

THz Response of Charge Carriers in Nanoparticles: Microscopic Master Equations Reveal an Unexplored Equilibration Current and Nonlinear Mobility Regimes

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However, the analysis of these experimental results with respect to the mobility of charge carriers (electrons or holes) is mostly done with bulk or phenomenological models like Drude, [8,10,26] Drude-Smith, [23,[27][28][29][30] or Monte-Carlo-based approaches. [31,32] Confinement to a finite system size has been shown to alter the initially Drude-like response of bulk systems to a Drude-Smith-like spectral response when an additional diffusive restoring current is introduced, resulting in a vanishing zero-frequency conductivity. In this context, the origin of the phenomenological back-scattering term in the Drude-Smith model is discussed.…”

“…On the other hand, THz transport nonlinearities have been considered infrequently in literature, however in bulk or systems with vanishing spatial carrier confinement. [ 31,46 ] In this contribution, we show that master equations are the appropriate formalism to treat the THz response of electrons in nanorods, which we exemplify for CdSe nanorods. The master equations offer a fully microscopic picture of the frequency‐dependent mobility, without introducing limits or approximations to applied field strength, phase, or thermal carrier distribution.…”