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The origin of intrinsic operational instability in organic field‐effect transistors (OFETs) is discussed by comparing bias stress effects of OFETs with unidirectionally aligned and unaligned active layers of two different semiconducting polymers under vacuum environment. By forming hydrophobic nano‐groove structures on gate dielectric surfaces, a high‐mobility donor–acceptor copolymer, poly[4‐(4,4‐dihexadecyl‐4H‐cyclopenta[1,2‐b:5,4‐b′]‐dithiophen‐2‐yl)‐alt‐[1,2,5]thiadiazolo[3,4‐c]pyridine] (PCDTPT) and a benchmark semicrystalline polymer, poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT‐C16), are successfully aligned. The mobilities of the PCDTPT‐OFETs are higher than those of the PBTTT‐OFETs, but the operational stabilities are lower. Moreover, for both semiconducting polymers, the aligned OFETs exhibit higher mobility but lower operational stability than the unaligned OFETs. These results indicate that an increase in mobility does not necessarily lead to an increase in operational stability. The interface trap density of states analysis reveals that the lower operational stability of PCDTPT‐OFETs is not due to the tail state change but primarily due to the much larger turn‐on voltage shift (ΔVon). The major mechanism causing ΔVon should be the charge carrier transfer from the channel to the gate dielectric. Since the energy barrier limiting the charge carrier transfer decreases with increasing ionization potential of the active layer, the lower operational stability of PCDTPT‐OFETs is attributed to the higher ionization potential of PCDTPT. [ABSTRACT FROM AUTHOR]

In this work, we systematically investigated the carrier transport of hysteresis-free amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) incorporating high- k (HfO2) x (Al2O3) y gate dielectrics with different composition and permittivity by atomic layer deposition. A dielectric surface morphology dominated interface scattering carrier transport mechanism is demonstrated, and the effect of the dielectric polarization and the interface states on the carrier mobility is discovered in TFT devices gated by high quality dielectrics with negligible charge trap effect. Accordingly, an a-IGZO TFT gated by (HfO2)0.5(Al2O3)0.5 dielectric with the smoothest surface exhibits the best performance in terms of a preferable field-effect mobility of 18.35 cm2 Vâˆ'1 sâˆ'1, a small subthreshold swing of 0.105 V decadeâˆ'1, a high on/off current ratio of 4.6 Ă— 106, and excellent stability under positive bias stress. [ABSTRACT FROM AUTHOR]

Revealing the intrinsic electrical properties is the basis of understanding new functional materials and developing their applications. However, in nonideal field‐effect transistors (FETs), conventional current–voltage characterizations do not accurately probe charge transport, particularly for newly developed semiconductors. Here, a generalized gated four‐probe (G‐GFP) technique is developed, which detects dynamic changes in carrier accumulation and transport. The technique is suitable for exploring the intrinsic properties of semiconductors in FETs with arbitrary contacts and in any operational regimes above the threshold. Application to simulated transistors confirms its accuracy in probing the evolution of channel potential, drift field, and gate‐dependent carrier mobility for devices with a contact‐limited operation and disordered semiconductors. Comparative experiments are performed based on FETs with various materials, device structures, and operational temperatures. The G‐GFP technique proves to exclude the various injection properties, to detect in situ how carriers are accumulated, and to clarify carrier mobility of the semiconductors. In particular, the well‐known "double‐slope" features in the current–voltage relations are controllably generated and their origins are identified. The approach could be used to explore electronic properties of newly developed materials such as organic, oxide, or 2D semiconductors. [ABSTRACT FROM AUTHOR]

For newly developed semiconductors, obtaining high‐performance transistors and identifying carrier mobility have been hot and important issues. Here, large‐area fabrications and thorough analysis of InGaZnO transistors with enhanced current by simple encapsulations are reported. The enhancement in the drain current and on–off ratio is remarkable in the long‐channel devices (e.g., 40 times in 200 µm long transistors) but becomes much less pronounced in short‐channel devices (e.g., 2 times in 5 µm long transistors), which limits its application to the display industry. Combining gated four‐probe measurements, scanning Kelvin‐probe microscopy, secondary ion mass spectrometry, X‐ray photoelectron spectroscopy, and device simulations, it is revealed that the enhanced apparent mobility up to several tens of times is attributed to the stabilized hydrogens in the middle area forming a degenerated channel area while that near the source‐drain contacts are merely doped, which causes artifact in mobility extraction. The studies demonstrate the use of hydrogens to remarkably enhance performance of oxide transistors by inducing a new mode of device operation. Also, this study shows clearly that a thorough analysis is necessary to understand the origin of very high apparent mobilities in thin‐film transistors or field‐effect transistors with advanced semiconductors. [ABSTRACT FROM AUTHOR]