Remarkable Mobility Increase and Threshold Voltage Reduction in Organic Field-Effect Transistors by Overlaying Discontinuous Nano-Patches of Charge-Transfer Doping Layer on Top of Semiconducting Film
Remarkable Mobility Increase and Threshold Voltage Reduction in Organic Field-Effect Transistors by Overlaying Discontinuous Nano-Patches of Charge-Transfer Doping Layer on Top of Semiconducting Film
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DOI：
10.1002/adma.201202789
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发表时间：
2013-02-06
影响因子：
29.4
通讯作者：
Park, Soo Young
中科院分区：
文献类型：
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作者：
Kim, Jong H.;Yun, Sun Woo;Park, Soo Young
在过去的十年里，有机场效应晶体管(OFET)因其在大面积、柔性电子器件中的高电势而引起了极大的实验和理论关注，例如电子纸显示器和射频识别标签(RFID)。[1]由于材料科学领域令人印象深刻的进步，许多优秀的场效应有机半导体被报道[2]，特别是高性能的并五苯基场效应晶体管[3]已经被密集地开发出来。然而，在大多数情况下，相当高的阈值电压(Vth)和仍然不足的迁移率(μ)水平仍然是实现高性能有机互补逻辑电路的挑战。[4]因此，迫切需要一种新颖的创新策略来同时提高有机半导体的阈值电压和迁移率。阈值电压被定义为陷阱和移动载流子之间平衡时的电压，其中位于价带边以上能隙内的所有分布陷阱被填充，因此精确控制OFET的阈值电压对于低电压操作集成电路的实际生产和使用是必要的。[5]已经展示了各种方法来改善OFET的阈值电压或载流子迁移率，例如采用高k栅绝缘体、自组装单层(SAM)栅介质体以及使用附加半导体层的双(三)层或混合层结构。由于其在器件制造过程中的高效率，由单个器件中顺序堆叠的p型和n型半导体层组成的层状结构受到了广泛的关注，特别是基于该器件方案，人们在开发具有良好平衡的空穴-电子迁移率的高性能双极OFET方面做出了广泛的努力。[7]在本研究中，我们将注意力转向通过覆盖不连续的电荷转移掺杂纳米贴片而不是渗漏覆盖层来同时显著地提高单极(空穴或电子)载流子迁移率和阈值电压，这应该决定了π−电子在界面区域的有效分子间交换[8]，同时保持了底层半导体的单极性质及其对−关断开关比的特性。通常，场效应晶体管在电荷载流子通过源−栅极电压(VG)积累后工作，称为电积累，其中积累的载流子(空穴或电子)的类型由VG的符号决定。[9]或者，OFET的操作也可以通过在宿主半导体中掺杂相反极性的掺杂剂来控制，这使得化学积累成为可能，并产生额外的可移动载流子。[8C]我们的工作策略是通过覆盖不连续的掺杂层纳米贴片在给定的半导体薄膜表面产生定向和单极的电荷转移掺杂，这应该通过有利的电荷积累和陷阱填充来影响迁移率和阈值电压。在此，我们系统地阐述了p型和n型场效应管的这一方法，以赋予高的载流子迁移率和可以忽略的阈值电压。推测界面电荷转移掺杂优先填充电荷陷阱，[10]降低了注入载流子跳跃输运过程的激活能(Ea)，并在有源沟道处积累了载流子。展示…的全部潜力
Organic field-effect transistors (OFETs) have attracted significant experimental and theoretical attention in the last decade because of their high potential as a fundamental switching component in large-area, flexible electronics devices, such as electronic paper display and radio-frequency identification tags (RFIDs).[1] Due to the impressive progress in the field of materials science, many excellent field-effective organic semiconductors [2] have been reported, and in particular high-performance pentacene-based OFETs [3] have been intensively developed. However, in most of the cases, rather high threshold voltage (Vth) and still insufficient mobility (μ) level remain a challenge for the realization of the high-performance organic complementary logic ciircuits.[4] Therefore, a novel and innovative strategy for the simultaneous enhancement of both threshold voltage and mobility of organic semiconductors is urgently required. Threshold voltage is defined as the voltage at the equilibrium between trapped and mobile carriers where all distributed traps lying within the energy band-gap above valence band edge are filled, and thus precise control of the threshold voltage of OFETs is necessary for the practical production and usage of low-voltage operating integrated circuits.[5] Various methods have been demonstrated in improving either the threshold voltage or charge carrier mobility of OFETs such as adopting high-k gate insulators, self-assembled monolayer (SAM) gate dielectrics, and bi-(tri-) layered or blended layer structures using an additional semiconducting layer.[4b, 6] Among them, due to its high efficiency in device fabrication process, layered structure, which is composed of sequentially stacked p-and n-type semiconductor layers in a single device, has received much attention, and in particular, extensive efforts have been made in the development of high-performance ambipolar OFETs exhibiting well balanced hole-electron mobility based on this device scheme.[7]In this study, we turned our attention to the simultaneous and remarkable enhancement of both unipolar (hole or electron) carrier mobility, rather than ambipolar transport, and threshold voltages by overlaying discontinuous nano-patches of charge-transfer doping layer instead of the percolated overlying layer, which should dictate the effective intermolecular exchange of π− electrons at the interfacial area,[8] while keeping the unipolar nature of underlying semiconductor with its characteristic on− off switching ratio. Generally, field-effect transistors operate after accumulation of charge carriers through a source− gate voltage (VG), called electrical accumulation, where the kind of accumulated carriers (hole or electron) is determined by the sign of VG.[9] Alternatively, operation of OFETs can also be controlled by doping opposite polarity dopant to the host semiconductor, which makes chemical accumulation possible and creates additional mobile charge carriers.[8c] Our strategy in this work is to create directional and unipolar charge-transfer doping on the surface of a given semiconducting film by overlaying discontinuous nano-patches of dopant layer, which should affect the mobility and threshold voltage via favorable charge accumulation and trap filling. Herein we present a systematic elaboration of this approach for both the p-and n-type OFETs to endow high charge carrier mobilities and negligible threshold voltages. It is speculated that the interfacial charge-transfer doping preferentially fills charge traps,[10] reduces activation energy (Ea) for the hopping transport process of the injected charge carriers, and accumulates mobile carriers at the active channels. To demonstrate the full potential …