| Posted: May 11, 2015 | |
Visualizing anisotropic carrier transport in organic semiconductor materials |
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| (Nanowerk News) Organic single crystal semiconductors have uniform crystal structures throughout their bulk. This means that any charge-carrying particles within the crystal will encounter different obstacles depending on their direction of travel (as an analogy, a stack of boxes looks different from different angles!). This property, known as mobility anisotropy, is very important to consider when using single crystals in the development of electronic devices. | |
| The most simple and direct method to measure charge carrier mobility, and therefore assess the level of mobility anisotropy within a crystal, is the current-voltage (IV) measurement. However, this requires large crystals, and cannot provide very high resolution for assessing the angular dependence. | |
| Now, Takaaki Manaka and Mitsumasa Iwamoto at Tokyo Institute of Technology have successfully visualized anisotropic carrier motion by using time-resolved microscopic optical second-harmonic generation (TRM-SHG) imaging (Applied Physics Express, "Direct Observation of Anisotropic Carrier Transport in Organic Semiconductor by Time-Resolved Microscopic Second-Harmonic Imaging"). | |
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| (a) Polarized microscopy image of round-shaped gold electrode. Time evolution of TRM-SHG images from round-shaped electrode at delay times of (b) 0, (c) 5, and (d) 10 ns. | |
| The light source for the TRM-SHG measurement was a femtosecond optical parametric amplifier. The round-shaped electrode that was deposited on the TIPS pentacene single crystalline domain was used to visualize the angular dependence of the carrier velocity at once. | |
| The elliptic shape of the SHG distribution directly represents the anisotropic carrier transport properties of the film, and the mobility anisotropy of this sample was evaluated as being 4.5. | |
| The TRM-SHG measurement is an effective method to investigate the anisotropic nature of carrier transport in practical devices. |
| Source: Tokyo Institute of Technology | |
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