Christian Lennartz | Searcharxiv

arXiv2017

Focus-Induced Photoresponse: a novel optoelectronic distance measurement technique

We present the Focus-Induced Photoresponse (FIP) technique, a novel approach to optical distance measurement. It takes advantage of a widely-observed phenomenon in photodetector devices: a nonlinear, irradiance-dependent photoresponse. This means that the output from a sensor is dependent on the total number of photons incident and the size of the area in which they fall. With a certain arrangement of sensor and lens, this phenomenon will cause the output of the sensor to change based on how far in or out of focus an object is. We call this the FIP effect. Here we demonstrate how to use the FIP effect for distance measurements. We show that this technique works with different sensor materials, device types, as well as visible and near infrared light. In principle, any sensor exhibiting a photoresponse that depends nonlinearly on irradiance could be used with the FIP technique. It is our belief that the FIP technique can become an important method for measuring distance.

physics.app-ph↗

arXiv2016

Anisotropic electron mobility studies on Cl2-NDI single crystals and the role of static and dynamic lattice deformations upon temperature variation

The anisotropic electron transport in the (001) plane of sublimation-grown Cl$_{2}$-NDI (naphthalene diimide) single crystals is analysed over a temperature range between 175 K and 300 K. Upon cooling from room temperature to 175 K the electron mobility along the direction of preferred transport monotonously increases from 1.5 cm$^{2}$/Vs to 2.8 cm$^{2}$/Vs according to a distinct temperature relation of $~T^{-1.3}$. At first glance, these characteristics allude to a coherent, i.e. band-like charge carrier transport predominantly governed by inelastic scattering with accoustic phonons. However, as we will demonstrate, the experimental mobility data can be consistently described within the framework of incoherent, hopping-type transport modeled by Levich-Jortner rates, explicitly accounting for the inner and outer relaxation energies related to thermally induced lattice effects and enhanced electron-phonon interaction at elevated temperatures. Complementary band-structure calculations yielding temperature dependent effective mass tensors deviate stronger from experimentally observed spatially anisotropic transport behavior. Thus, these results hint at the fact that by the particular interplay of the transport energies the mobility of a given organic semiconducting material might appear to be band-like in a certain temperature regime even though the underlying charge carrier transport can be of incoherent, hopping-type nature. Building on this description, we further explore the role of the intermolecular electronic coupling and develop a procedure to distinguish between its dependence on static and dynamic lattice deformation upon temperature variation.

cond-mat.mtrl-sci↗