Defect healing at room temperature in pentacene thin films and improved transistor performance

Kalb, Wolfgang L.; Meier, Fabian; Mattenberger, K.; Batlogg, B.

doi:10.1103/physrevb.76.184112

Cited by 71 publications

(64 citation statements)

References 52 publications

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“…charge transport has been proposed and widely accepted, 13,14 and there have been many attempts to determine the trap density of states (trap DOS). However, the trap DOS has been analyzed mainly for p-channel materials, [13][14][15][16][17][18][19][20] and comparatively limited works have been done for n-channel materials. 15,[21][22][23] In particular, the trap DOS has not been systemically studied from the viewpoint of the basic transistor operation.…”

Section: Introductionmentioning

confidence: 99%

“…Lang et al have extracted the trap DOS from the Arrhenius plot of the transconductance for single-crystal pentacene transistors, 32,33 and similar analysis has been applied to other thin-film organic semiconductors. 15,16 In addition, a variety of methods to calculate the trap DOS have been investigated, and an exponential distribution of the DOS has been established in pentacene thin-film transistors, [17][18][19] and in single crystal transistors. 20 The DOS distribution has been also extracted from space-charge-limited-current spectroscopy and Kelvin probe microscopy.…”

Section: Introductionmentioning

confidence: 99%

“…Intrinsic carrier transport, in particular, band transport, has been explored in organic single crystals, [9][10][11][12] and trap-limited charge transport has been examined in organic thin films, which have higher density of trap states due to the structural defect, grain boundaries, and chemical impurities. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The multiple trapping and release model for a Author to whom correspondence should be addressed. Electric mail: cho.j.ad@m.titech.ac.jp.…”

Section: Introductionmentioning

confidence: 99%

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Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

et al. 2013

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We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N ’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

et al. 2013

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“…[10][11][12][13][14][15][16][17] Kalb et al have analysed organic transistors based on these methods and proved that various methods afford approximately consistent exponential trap distribution. [24][25][26][27][28] Although Lang's analysis has been extensively used due to its simpleness for (4)). The free carriers Q f are activated from E F to the interface E c according to Eq.…”

Section: Introductionmentioning

confidence: 99%

Analysing organic transistors based on interface approximation

Akiyama

Mori

2014

AIP Advances

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Temperature-dependent characteristics of organic transistors are analysed thoroughly using interface approximation. In contrast to amorphous silicon transistors, it is characteristic of organic transistors that the accumulation layer is concentrated on the first monolayer, and it is appropriate to consider interface charge rather than band bending. On the basis of this model, observed characteristics of hexamethylenetetrathiafulvalene (HMTTF) and dibenzotetrathiafulvalene (DBTTF) transistors with various surface treatments are analysed, and the trap distribution is extracted. In turn, starting from a simple exponential distribution, we can reproduce the temperature-dependent transistor characteristics as well as the gate voltage dependence of the activation energy, so we can investigate various aspects of organic transistors self-consistently under the interface approximation. Small deviation from such an ideal transistor operation is discussed assuming the presence of an energetically discrete trap level, which leads to a hump in the transfer characteristics. The contact resistance is estimated by measuring the transfer characteristics up to the linear region.

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“…This is likely to be originated from the interface charges between the pentacene layer and the cowl-shaped nanostructures. Considering that the flat band voltage (VFB) can be approximated to the onset voltage (V onset ) of the device [13], the density of trapped holes can be estimated using C ins (ΔV TH −ΔV FB )/q because V TH above V onset is an estimate of the trap density in the channel [14], where Cinsis the capacitance of gate insulator; using this approach, the density of trapped holes was found to be about 2.4×10 11 cm −2 .It is presumed that polyurethane molecules might induce an energetic disorder at the interface. Further investigation is required to elucidate the origin of such interface charges.…”

mentioning

confidence: 99%

Pentacene Thin-Film Transistors with Hydrophobic Nanostructures on a Polymeric Gate Insulator

Kim¹,

Lee²,

Park³

2015

Int J Metall Mater Eng

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The effects of hydrophobic nanostructures on the growth of pentacene molecules and the electrical characteristics of pentacene thin-film transistors (TFTs) are investigated. X-ray diffraction results show that hydrophobic nanostructures are conducive to the upright growth of pentacene molecules to the substrate. Pentacene TFTs, in which hydrophobic nanostructures with a cowl shape were introduced at the interface between the pentacene layer and the gate insulator, thus exhibit a pronounced enhancement in the field-effect mobility, up to approximately 2.94 cm 2 /Vs. These results suggest that hydrophobic nanostructures are effective to the ordered growth of pentacene molecules for high-performance organic TFTs. Pentacene Thin-Film Transistors with Hydrophobic Nanostructures on a Polymeric Gate Insulator Keywords:Organic semiconductor, Thin-film transistor, Molecular ordering Research ArticleOpen Access IntroductionOrganic thin-film transistors (TFTs) are attracting much interest because of their simple and low-temperature process ability. It is envisaged that they will have enormous market in a wide range of applications, for example as the driving elements for flexible displays, radio-frequency identification tags and large area sensors [1][2][3]. Previous investigations on organic TFTs have focused on materials [4], interfacial properties [5], source/drain contact engineering [6] and processing techniques [7], to enhance the TFT performance. Among the characteristic parameters, the field-effect mobility is known to be greatly influenced by the deposition conditions and consequent crystallinity of organic semiconductors. Likewise, the chemical and morphological properties of a gate insulator are deemed decisive to the field-effect mobility in bottom-gate organic TFTs by influencing the crystalline growth of an organic semiconductor. Several works have shown that the rough surface of a gate insulator causes a reduction in the field-effect mobility [5,8]. In contrast, recent studies reported that the crystalline growth of organic semiconductors and the performance of organic TFTs can be improved by introducing structured morphologies on the surface of a gate insulator [9,10], which motivates our research into cowl-shaped nanostructures for application in organic TFTs.In this study, we show that hydrophobic nanostructures with a cowl shape facilitate the upright growth of pentacene molecules to the substrate. The influence of hydrophobic cowl-shaped nanostructures on the morphological and structural characteristics of pentacene films are investigated. The enhancement in the field-effect mobility of pentacene-based TFTs fabricated with these nanostructures is reported. Experimental ProcedureTo fabricate pentacene TFTs, a 150-nm-thick Al gate was deposited on a glass substrate using the first shadow mask. Poly (4-vinylphenol) (PVP) with a cross-linking agent was spin-coated on the gate-patterned substrates and baked consecutively at 175°C for 1 h in a vacuum oven. A 480-nm-thick layer of cross-linked PVP (cP...

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Defect healing at room temperature in pentacene thin films and improved transistor performance

Cited by 71 publications

References 52 publications

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

Analysing organic transistors based on interface approximation

Pentacene Thin-Film Transistors with Hydrophobic Nanostructures on a Polymeric Gate Insulator

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