Thermoelectric contributions to electronic transport and THz responsivity of TeraFETs –simulations and experiments

天线耦合场效应晶体管（fet）成功地成为太赫兹（THz）辐射的敏感探测器。探测机制是基于FET通道中等离子体增强的分布电阻混合（Dyakonov-Shur机制），结合能量和电荷输运的扩散贡献引起的热电热载子效应。在本项目的第一阶段，我们扩展了不考虑热效应的流体动力学Dyakonov-Shur模型，利用矩量法从玻尔兹曼方程导出了电荷和能量输运的流体动力学模型。基于fet的电流/电压特性，我们还开发了石墨烯fet的电荷电压模型（对于其他材料系统，我们之前已经导出了它们）。完整的物理模型及其描述电荷和能量输运的四个微分方程在电路仿真工具Keysight ADS中对Si， GaN， GaAs和石墨烯材料系统进行了实现。作为仿真的输入参数，只需要从晶体管的直流测量和天线仿真中提取数据。该模型以接近定量的方式再现了探测器在各种材料系统中从0.1太赫兹到至少4太赫兹的测量太赫兹响应率和噪声等效功率。可以确定热电效应在III/V材料体系和石墨烯中制造的晶体管中的贡献；对于III/Vs，它在栅极电压的工作点是有害的。在我们现在申请资助的项目的第二阶段，我们的目标是各种模型的改进。其中之一涉及直流和太赫兹频率下通道边界电位分布的细节。预计交流电位分布将强烈影响扩散输运，从而影响热电效应。研究的另一个主题是高辐射强度下的饱和效应。进一步的改进主要针对石墨烯器件，并涉及与芬兰阿尔托大学的一个团队的密切合作。通过专门设计的器件结构，我们的目标是提取更可靠的电荷载流子的能量弛豫率数据。利用先进的模型，我们将着手设计优化的基于石墨烯的探测器结构，由Aalto团队实施，并由Aalto和我们进行测量。该项目的一个重要部分还将用于准备以下出版物：(i)关于模拟工具、其基础物理模型假设及其在ADS中的算法实现，（ii）关于模拟工具在设备性能分析中的应用，以及（iii）关于它在改进探测器开发中的预测性使用。

Antenna-coupled field-effect transistors (FETs) establish themselves successfully as sensitive detectors of terahertz (THz) radiation. The detection mechanism is based on plasmon-enhanced distributed resistive mixing in the FET's channel (Dyakonov-Shur mechanism) in combination with thermoelectric hot-carrier effects arising from diffusive contributions to energy and charge transport. Extending the hydrodynamic Dyakonov-Shur model, which does not take thermal effects into account, we derived in the first phase of this project a hydrodynamic model for charge and energy transport from the Boltzmann equation using the method of moments. Based on the current/voltage characteristics of the FETs, we also developed a charge-voltage model for graphene FETs (for other material systems, we had derived them earlier). The complete physical model with its four differential equations describing charge and energy transport was implemented in the circuit simulation tool Keysight ADS for the material systems Si, GaN, GaAs and Graphene. As input parameters for the simulations, only data extracted from DC measurements of the transistors and antenna simulations are needed. The model was found to reproduce the measured THz responsivity and noise-equivalent power of detectors in various material systems in a near-quantitative manner from 0.1 THz up to at least 4 THz. The contribution of the thermoelectric effect in transistors made in the III/V material systems and in Graphene could be determined; for III/Vs, it is detrimental at the operation points of the gate voltage.In the second phase of the project, for which we apply for funding now, we aim at various model refinements. One of them relates to the details of the potential distribution at the channel’s boundaries both at DC and THz frequencies. The AC potential distribution is expected to strongly influence the diffusive transport and thus the thermoelectric effect. Another subject of the studies will be saturation effects at high radiation intensities. Further refinements are mainly for graphene devices and involve a close cooperation with a team at Aalto University, Finland. With specifically designed device structures, we aim for the extraction of more robust data for the energy relaxation rates of the charge carriers. Using the advanced model, we will then embark on the design of optimized graphene-based detector structures, to be implemented by the Aalto team and to be measured at Aalto and by us. A significant part of the project will also be devoted to the preparation of publications (i) on the simulation tool, its underlying physical model assumptions and its algorithmic implementation in ADS, (ii) on the application of the simulation tool for the analysis of device performance, and (iii) on the predictive use of it for the development of improved detectors.