arXiv subjects

K. Meerholz

Publications and source records attributed to K. Meerholz.

5 recordsLinked to original sources

arXiv2023

Parametrization of the Charge-Carrier Mobility in Organic Disordered Semiconductors. APAE against EGDM

An appropriately parameterized compact analytical equation (APAE) is suggested to account for charge carrier mobility in organic disordered semiconductors (ODSs). This equation correctly reproduces the effects of temperature $T$, carrier concentration $n$, and electric field $F$ on the carrier mobility $μ(T,F,n)$, as evidenced by comparison with analytical theories and Monte Carlo simulations. The set of material parameters responsible for charge transport is proven to be at varience to those used in the so-called extended Gaussian disorder model (EGDM) approach, which is widely exploited in commercially distributed device--simulation algorithms. While EGDM is only valid for cubic lattices with a specific choice of parameters, APAE describes charge transport in systems with spatial disorder in a wide range of parameters. APAE is user-friendly and, thus, suitable for incorporation into device-simulation algorithms.

cond-mat.soft↗

arXiv2023

Quantum states in disordered media. I. Low-pass filter approach

The current burst in research activities on disordered semiconductors calls for the development of appropriate theoretical tools that reveal the features of electron states in random potentials while avoiding the time-consuming numerical solution of the Schrödinger equation. Among various approaches suggested so far, the low-pass filter approach of Halperin and Lax (HL) and the so-called localization landscape technique (LLT) have received most recognition in the community. We prove that the HL approach becomes equivalent to the LLT for the specific case of a Lorentzian filter when applied to the Schrödinger equation with a constant mass. Advantageously, the low-pass filter approach allows further optimization beyond the Lorentzian shape. We propose the global HL filter as optimal filter with only a single length scale, namely, the size of the localized wave packets. As an application, we design an optimized potential landscape for a (semi-)classical calculation of the number of strongly localized states that faithfully reproduce the exact solution for a random white-noise potential in one dimension.

cond-mat.dis-nn↗

arXiv2023

Quantum states in disordered media. II. Spatial charge carrier distribution

The space- and temperature-dependent electron distribution $n(\mathbf r,T)$ is essential for the theoretical description of the opto-electronic properties of disordered semiconductors. We present two powerful techniques to access $n(\mathbf r,T)$ without solving the Schrödinger equation. First, we derive the density for non-degenerate electrons by applying the Hamiltonian recursively to random wave functions (RWF). Second, we obtain a temperature-dependent effective potential from the application of a universal low-pass filter (ULF) to the random potential acting on the charge carriers in disordered media. Thereby, the full quantum-mechanical problem is reduced to the quasi-classical description of $n(\mathbf r,T)$ in an effective potential. We numerically verify both approaches by comparison with the exact quantum-mechanical solution. Both approaches prove superior to the widely used localization landscape theory (LLT) when we compare our approximate results for the charge carrier density and mobility at elevated temperatures obtained by RWF, ULF, and LLT with those from the exact solution of the Schrödinger equation.

cond-mat.dis-nn↗

arXiv2022

Comment on "Interplay of Structural and Optoelectronic Properties in Formamidinium Mixed Tin-Lead Triiodide Perovskites"

Studying optoelectronic properties in FAPb$_{1-x}$Sn$_x$I$_3$ perovskites as a function of the lead:tin content, Parrott et al. observed the broadest luminescence linewidth and the largest luminescence Stokes shift in mixed compositions with Sn $ < 25$% and with $> 0.85$%. Since the largest effects of alloy disorder were expected for the 50:50 composition, it was concluded that the revealed disorder effects might arise from extrinsic factors that can be eliminated upon further crystal growth optimization. This comment shows that the largest effects of alloy disorder for perfectly random fluctuations in FAPb$_{1-x}$Sn$_x$I$_3$ perovskite are, in fact, expected for $x < 0.25$ and for $x > 0.85$. Therefore, further crystal growth optimization is futile.

cond-mat.mtrl-sci↗

arXiv2017

Plasmonic enhancement of aligned semiconducting graphene nanoribbons

We couple photoluminescent semiconducting 7-atom wide armchair edge graphene nanoribbons to plasmonic nanoantenna arrays and demonstrate an enhancement of the photoluminescence and Raman scattering intensity of the nanoribbons by more than one order of magnitude. The increase in signal allows us to study Raman spectra with high signal-to-noise ratio. Using plasmonic enhancement we are able to detect the off-resonant Raman signals from the modified radial breathing-like mode (RBLM) due to physisorbed molecules, the 3rd order RBLM, and C-H vibrations. We find excellent agreement between data and simulations describing the spectral dependence of the enhancement and modifications of the polarization anisotropy. The strong field gradients in the optical near-field further allow us to probe the subwavelength coherence properties of the phonon modes in the nanoribbons. We theoretically model this considering a finite coherence length along the GNR direction. Our results allow estimating the coherence length in graphene nanoribbons.

physics.optics↗