Electron and spin transport studies of gated lateral organic devices

Abstract

Articles you may be interested inSpin-dependent transport behavior in C60 and Alq3 based spin valves with a magnetite electrode (invited) J. Appl. Phys. 115, 172608 (2014) In view of the many, often contradictory, reports of magneto-resistance (MR) in spin valve stacks containing a layer of organic semiconductor, mostly of the small molecule variety, we have investigated interdigitated lateral structures with an organic layer deposited in the narrow gap between two ferromagnetic electrodes, which are well-suited for studying charge and spin transport in novel (high resistivity) semiconducting materials. For the channel material we used three different organic semiconductors, the small molecule tris-(8-hydroxyquinoline) aluminum (Alq3), single crystals of pentacene, and the conductive polymer poly(3-hexylthiophene) (P3HT). The channel length was 80 nm. Temperature-dependent current-voltage characteristics reveal that in all instances the current is limited by field-assisted thermionic injection over an energy barrier at the metal/organic interface. No measurable magneto-resistance was observed down to 7 K. The interface energy barrier, together with the vastly different electronic structure of metals and organics close to the Fermi level, preclude spin injection. Nonetheless, unlike the case of inorganic semiconductors, the insertion of an artificial tunnel barrier at the contact did not improve spin injection. Gate-dependent measurements exhibited shortchannel effects and transistor operation with on/off ratios of 10 3 , but no magneto-resistance. We suggest the observations are a consequence of the formation of bipolaron-states at increasing carrier concentration. V C 2012 American Institute of Physics. [http://dx

Impurity-band transport in organic spin valves

“…Lateral ferromagnet-organic-ferromagnet devices, where both electrodes are fabricated before the deposition of the organic, however, are much more resistive and seldom exhibit any spin-valve effect 19 . While the I-V characteristics in the vertical OSVs is drastically different from what is expected from a Mott diode, it is strikingly similar to that of metal-inorganic insulator-metal devices, fabricated in a similar manner as the OSVs.…”

Effects of conjugated polymer on the magnetotransport properties in La0.7Sr0.3MnO3 ferromagnetic electrodes

“…There have been numerous reports on limitations, caused by e.g. Schottky barriers, formation of spin-less bipolarons and Fermi level pinning due to localized states, [6][7][8] regarding efficient spin polarized (SP) injection from inorganics into organics. This debate has enforced the need for more detailed studies of organic/inorganic interfaces and their ability to affect spin transport and injection.…”

Strategies for Fabricating Nanogap Single-Crystal Organic Transistors

“…A high-impedance setup was necessary, due to the low mobility and carrier concentration, which is typical of intrinsic organic semiconductors. Electrical characterization and transistor operation are reported elsewhere [16]; here we aimed at describing in detail the fabrication process used to make our short-channel organic devices.…”