We study variation in mobility measurements on organic films. Values extracted by different scientists typically vary by about mobility and conductivity in semiconductors pdf factor of 3. We propose a protocol that drastically reduces this variation. Control of film thickness and electrode quality are also important factors.
Charge carrier mobility is a figure of merit commonly used to rate organic semiconducting materials for their suitability in applications such as solid-state lighting or photovoltaics. Although large variations are found in published mobility values on identical materials, there is little open discussion in the literature of the reproducibility of these results. We address this with an interlaboratory study of mobility measurements performed on a set of organic semiconductors using the space-charge limited current method. We found mobility measured on nominally identical devices could vary by more than one order of magnitude, with the largest sources of variation being poor electrodes and film thickness variation. Moreover, we found that mobility values extracted from identical data by different scientists would typically vary by a factor of 3. We also present general guidelines for improving the reproducibility of benchmark mobility measurements. 2014 Published by Elsevier B.
A number of technical applications require high mobilities. For high purity single crystals, a steep increase of mobilities towards low temperature with the consequence of nonlinear transport and final velocity saturation at elevated electric fields has been found and traced back to temperature-dependent electron and hole masses approaching the free electron mass at low temperature. For crystals with orientational disorder of the molecules band transport is precluded. Check if you have access through your login credentials or your institution.
Unsourced material may be challenged and removed. This process is known as doping and resulting semiconductors are known as doped or extrinsic semiconductors. Doping greatly increases the number of charge carriers within the crystal. The semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants.
Some of the properties of semiconductor materials were observed throughout the mid 19th and first decades of the 20th century. These modifications have two outcomes: n-type and p-type. These refer to the excess or shortage of electrons, respectively. An unbalanced number of electrons would cause a current to flow through the material.
This results in an exchange of electrons and holes between the differently doped semiconducting materials. The n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. A difference in electric potential on a semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. Whenever thermal equilibrium is disturbed in a semiconducting material, the number of holes and electrons changes.
In certain semiconductors, excited electrons can relax by emitting light instead of producing heat. Silicon and germanium are used here effectively because they have 4 valence electrons in their outermost shell which gives them the ability to gain or lose electrons equally at the same time. Groups 12 and 16, groups 14 and 16, and between different group 14 elements, e. Certain ternary compounds, oxides and alloys.