Improving organic transistor performance through contact-area-limited doping

Li, Jun; Zhang, Xiaowen; Zhang, Liang; Khizar-ul-Haq,; Jiang, Xue-Yin; Zhu, Wenqing; Zhang, Zhilin

doi:10.1016/j.ssc.2009.07.006

Cited by 35 publications

(27 citation statements)

References 18 publications

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“…If the energy of the lowest unoccupied molecular orbital (LUMO) of the dopant molecules is near (ideally below) the energy of the highest occupied molecular orbital (HOMO) of the host semiconductor, electrons can move from the host semiconductor to the dopant molecules, thereby creating excess holes in the semiconductor and thus increasing its electrical conductivity 18–22. This concept has previously been applied to organic p‐channel TFTs with channel lengths down to 300 nm 23–28. In all these reports, however, the gate electrode of the TFTs was not patterned.…”

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confidence: 99%

“…Since we cannot measure the orbital energies at the DNTT/NDP‐9 interface, we have to rely on conclusions from other measurements to elucidate the energy lineup at the DNTT/NDP‐9 interface. SI, Figure S4, summarizes the results of several measurements we have carried out to compare the doping strength of NDP‐9 to that of an organic dopant that has been previously employed in organic TFTs, 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F 4 ‐TCNQ) 26, 27. We found that the sheet resistance of a 30 nm‐thick DNTT layer doped with NDP‐9 (nominally 1 nm thick) is a factor of 7 smaller than the sheet resistance of a 30 nm‐thick DNTT layer doped with F 4 ‐TCNQ (also nominally 1 nm thick; SI, Figure S4a).…”

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confidence: 99%

“…A major concern with area‐selective doping in organic TFTs is the positional stability of the dopants. If the dopants were to drift or diffuse into the channel, the resulting channel doping would produce large off‐state currents 24, 27, 28 . Figure shows results from a bias‐stress measurement performed on a submicrometer TFT (channel length 150 nm) with contact doping.…”

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confidence: 99%

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Contact Doping and Ultrathin Gate Dielectrics for Nanoscale Organic Thin‐Film Transistors

Ante

Kälblein

Zschieschang

et al. 2011

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127

117

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To suppress undesirable short‐channel effects in organic transistors with nanoscale lateral dimensions, aggressive gate‐dielectric scaling (using an ultra‐thin monolayer‐based gate dielectric) and area‐selective contact doping (using a strong organic dopant) are introduced into organic transistors with channel lengths and gate‐to‐contact overlaps of about 100 nm. These nanoscale organic transistors have off‐state drain currents below 1 pA, on/off current ratios near 107, and clean linear and saturation characteristics.

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Contact Doping and Ultrathin Gate Dielectrics for Nanoscale Organic Thin‐Film Transistors

Ante

Kälblein

Zschieschang

et al. 2011

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“…In the case of p-channel OTFTs, strong acceptor molecules such as ferric chloride (FeCl 3 ), 3-5 molybdenum trioxide (MoO 3 ), 6,7 and 2,3,5,6tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) [8][9][10][11] are doped into the interface between the contact electrode and the active p-type semiconductor layer in order to form hole-doped interface layers, thereby resulting in lowering of the hole injection barrier or the bulk resistance. 1,2 Contact-area-limited doping has been widely studied and employed to enhance the charge carrier injection from a contact electrode to a semiconductor layer.…”

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confidence: 99%

Experimental and numerical investigation of contact-area-limited doping for top-contact pentacene thin-film transistors with Schottky contact

Noda

Wada

Toyabe

2015

Phys. Chem. Chem. Phys.

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Effects of contact-area-limited doping for pentacene thin-film transistors with a bottom-gate, top-contact configuration were investigated. The increase in the drain current and the effective field-effect mobility was achieved by preparing hole-doped layers underneath the gold contact electrodes by coevaporation of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), confirmed by using a thin-film organic transistor advanced simulator (TOTAS) incorporating Schottky contact with a thermionic field emission (TFE) model. Although the simulated electrical characteristics fit the experimental results well only in the linear regime of the transistor operation, the barrier height for hole injection and the gate-voltage-dependent hole mobility in the pentacene transistors were evaluated with the aid of the device simulation. This experimental data analysis with the simulation indicates that the highly-doped semiconducting layers prepared in the contact regions can enhance the charge carrier injection into the active semiconductor layer and concurrent trap filling in the transistor channel, caused by the mitigation of a Schottky energy barrier. This study suggests that both the contact-area-limited doping and the device simulation dealing with Schottky contact are indispensable in designing and developing high-performance organic thin-film transistors.

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“…[1][2][3] Recently, the improvement of device performance in top-contact p-channel organic thin-film transistors was demonstrated by contact-area-limited doping, where an electron-acceptor-doped layer was formed at the interface between a semiconductor layer and a contact electrode. [4][5][6][7] Since these molecular doping methods have been employed for controlling the electrical conductivity of organic semiconductors, [8][9][10][11][12] it has been commonly considered that p-type doping of the organic layer causes the decrease of the contact resistance and the hole injection barrier. However, it was also reported that acceptor=electrode charge transfer (without any organic=organic charge transfer) can also mimic p-type doping of the organic layer.…”

Section: Introductionmentioning

confidence: 99%

Molecular doping effect in bottom-gate, bottom-contact pentacene thin-film transistors

Wakatsuki

Noda

Wada

et al. 2011

Journal of Applied Physics

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A bottom-gate, bottom-contact (BGBC) organic thin-film transistor (OTFT) with carrier-doped regions over source-drain electrodes was investigated. Device simulation with our originally developed device simulator demonstrates that heavily doped layers (p+ layers) on top of the source-drain contact region can compensate the deficiency of charge carriers at the source-channel interface during transistor operation, leading to the increase of the drain current and the apparent field-effect mobility. The phenomena expected with the device simulation were experimentally confirmed in typical BGBC pentacene thin-film transistors. The 5-nm-thick p+ layers, located 10 nm (or 20 nm) over the source-drain electrodes, were prepared by coevaporation of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an acceptor dopant. Since the molecular doping in this study can increase the drain current without positive shift of threshold voltage, p+ layers were formed precisely on top of the source-drain regions. This study shows that common inferior characteristics of bottom-contact OTFT devices mainly derive from the supply shortage of charge carriers to the channel region. The importance of reliable molecular doping techniques or heavily doped semiconductor materials for improving OTFT device performance is clearly suggested.

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Improving organic transistor performance through contact-area-limited doping

Cited by 35 publications

References 18 publications

Contact Doping and Ultrathin Gate Dielectrics for Nanoscale Organic Thin‐Film Transistors

Contact Doping and Ultrathin Gate Dielectrics for Nanoscale Organic Thin‐Film Transistors

Experimental and numerical investigation of contact-area-limited doping for top-contact pentacene thin-film transistors with Schottky contact

Molecular doping effect in bottom-gate, bottom-contact pentacene thin-film transistors

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