Minority and Majority Charge Carriers in Organic-Field Effect Transistors

摘要非技术：有机场效应晶体管(OFET)是用于可穿戴电子设备或柔性显示器等柔性和低成本电子产品的关键技术。然而，OFET面临着严重的障碍，延缓了它们的商业化进程。有机半导体的掺杂为OFET技术开辟了一个新的视角。这种额外的自由度允许实现新的器件概念，并克服目前OFET技术的局限性。为了充分利用掺杂对OFET的好处，必须显著降低0.1-1%范围内的电流掺杂率。该项目解决了这一挑战。将优化掺杂工艺，将掺杂水平降低到低于100ppm的范围。在这些超低掺杂浓度下，将深入研究掺杂对晶体管行为的影响：a)将开发一个描述掺杂有机晶体管中载流子积累和耗尽的定量模型；b)将研究在超低掺杂浓度下少数载流子的产生；c)将实现一个新的器件概念-有机隧道场效应晶体管-将评估其潜力。为了扩大该项目的影响，将采取额外措施增加少数族裔学生的参与。将提供暑期项目，这将为来自代表性不足群体的本科生提供机会，了解实验研究，并告知他们研究生院的潜在选择。此外，研究项目将通过大学学分+计划提供给当地的高中生，研究生将接受高度跨学科领域的培训。技术：掺杂有机半导体为OFET的设计提供了一个新的维度，并具有实现新器件概念和提高性能的潜力。鉴于这些前景，本项目的研究目标是研究掺杂对场效应管的影响，并对掺杂场效应管中多数和少数载流子的产生和复合有更好的了解。为了实现这一目标，人们致力于以下目标：a)开发一个描述掺杂有机晶体管中大多数载流子积累和耗尽的一致且经过实验验证的模型；b)研究掺杂有机晶体管中的非均匀载流子动力学，并阐明少数载流子产生和复合的机制；以及c)利用掺杂电势，实现垂直有机隧道场效应晶体管(VOTFET)。在本项目中，引入了一种能够在低于100ppm的范围内控制掺杂浓度的旋转快门系统，从而开启了一种新的掺杂制度。通过电容-电压测量、光电子能谱和晶体管表征，研究了在这些超低掺杂浓度下掺杂对平带、阈值和夹断电压的影响。在有机金属氧化物半导体结构和有机晶体管中研究了少数载流子的产生，而在p-n-i-p结构中研究了非均匀载流子的寿命和扩散长度。通过系统的器件变化来研究VOTFET的工作机理。特别是，隧道注入机制将通过增加本征半导体层的厚度来验证。这些实验将有可能推进该领域的知识：a)将澄清少数载流子产生的机制；b)将测试描述平带电压对阈值和夹断电压的影响的分析模型；c)将详细了解少数载流子扩散，并将研究少数载流子的寿命如何取决于掺杂浓度和温度；d)将验证描述掺杂OFET中电流饱和的新的解析解。

AbstractNontechnical:Organic Field-Effect Transistors (OFETs) are a key technology for flexible and low-cost electronics used e.g. for wearable electronics or flexible displays. However, OFETs are facing severe obstacles that delay their commer-cialization. Doping of organic semiconductors opens a new perspective on the OFET technology. This additional degree of freedom allows to realize new device concepts and to overcome current limitations of the OFET tech-nology. To take full advantage of the benefits of doping for OFETs, current doping ratios in the range of 0.1-1% have to be reduced significantly. The project addresses this challenge. Doping processes will be optimized to re-duce the doping level into the sub-100 ppm range. At these ultra-low doping concentrations, the influence of dop-ing on transistor behavior will be studied thoroughly: a) A quantitative model will be developed to describe charge carrier accumulation and depletion in doped organic transistors; b) Generation of minority charge carriers at ul-tralow doping concentrations will be studied; c) A new device concept - the organic tunnel field-effect transistor - will be realized, and its potential will be evaluated.To broaden the impact of the project, additional measures will be taken to increase the participation of minority students. Summer projects will be offered, which will provide undergraduate students from underrepresented groups with the opportunity to learn about experimental research and to inform them about potential choices for graduate school. Furthermore, research projects will be offered to local high-school students through the college credit plus program, and graduate students will be trained in a highly interdisciplinary field.Technical:Doping organic semiconductors provides a new dimension in the design of OFETs and bears the potential of ena-bling new device concepts with increased performance. In light of these prospects, the research goal of this project is to study the influence of doping on OFETs and to provide an improved understanding of majority and minority charge carrier generation and recombination in doped OFETs. To reach this aim, the following objectives are pursued: a) to develop a consistent and experimentally validated model describing majority charge carrier accumulation and depletion in doped organic transistors; b) to study mi-nority charge carrier dynamics in doped organic transistors and clarify the mechanism of minority charge carrier generation and recombination; and c) to leverage on the potential of doping and realize vertical organic tunnel field-effect transistors (VOTFETs).Doping organic transistors necessitates the use of much lower doping concentrations as commonly used in organic devices. In this project, a rotating shutter system capable of controlling doping concentrations in the sub 100 ppm regime is introduced, which opens a new regime of doping. The influence of doping on the flatband, threshold, and pinch-off voltage at these ultra-low doping concentrations is studied by capacitance vs. voltage measurements, photoelectron spectroscopy, and transistor characterization. Minority charge carrier generation is studied in organ-ic metal-oxide-semiconductor structures and organic transistors, whereas the lifetime and diffusion length of mi-nority charge carriers are characterized in p-n-i-p structures. The operation mechanism of VOTFETs will be stud-ied by systematic device variations. In particular, the tunnel injection mechanism will be validated by an increase in the thickness of the intrinsic semiconductor layer.These experiments have the potential to advance the knowledge in the field: a) The mechanism of minority charge carrier generation will be clarified; b) An analytical model describing the influence of the flatband voltage on the threshold and pinch-off voltage will be tested; c) A detailed understanding of minority charge carrier diffusion will be developed and it will be studied how the lifetime of minority charge carriers depends on the doping con-centration and temperature; d) A new analytical solution describing current saturation in doped OFETs will be verified.