Modeling and Optimization of Ultrafast and Low-Noise Thin Avalanche Photodiodes for Optical Communications

这项研究计划是一项理论和实验交叉学科的努力，将导致新一代超快和高精度光电探测器的设计。该计划将重点放在被称为薄雪崩光电二极管(APD)的广泛使用的光电探测器类别上。该计划的动机是满足下一代光核心网络对带宽日益增长的需求，下一代光核心网络需要开发具有远远超出当前最先进水平的增益带宽产品的新一代低噪声和高响应度光电探测器。此外，由于光波网络的能力最终受到其体系结构和组件性能的限制，因此彻底了解适用的光电探测器的基本性能限制将对未来通信网络的设计产生重大影响。此外，随着宽带隙材料技术在各种高精度和超快传感应用中的兴起，有必要开发使用宽带隙材料的高性能光电探测器，如CAN。本项目的第一个目标是开发和验证一个严格的基于更新理论的模型，用于联合统计APDS的增益和响应时间。该模型将适用于各种结构和材料的APDS，特别是具有低倍增噪声和高带宽的薄型APDS。该理论将具体捕捉死区的重要影响，死区在薄型APD的性能中起主要作用，并显著影响超快(码间干扰受限)和批次功率(增益波动受限)应用的性能。通过减小雪崩光电二极管倍增层的厚度，可以显著改善噪声和带宽特性，而倍增层是器件增益的主要来源。到目前为止，薄APD的增益-带宽乘积的统计的基本极限，以及更值得注意的是，减少倍增层的厚度对响应时间波动的影响仍然未知。该项目的第二个目标是利用开发的模型来设计和开发下一代高性能的雪崩光电二极管。器件制造和表征将在奥斯汀得克萨斯大学微电子研究中心的现有设施中进行。将深入研究器件雪崩倍增层的厚度所起的作用，以努力设计具有特定用途的最佳特性的器件。该计划将开发增益带宽产品远超过500 Chz(带宽为50-100 GHz)的低噪声设备。优化标准将包括a)在固定误码率下最大化数据传输速率，这适用于符号间干扰受限的通信系统，以及b)在功率受限的侦听应用中最大化接收器的信噪比。作为实现上述目标的工具，将设计一个由定制的并行计算算法组成的CAD工具，旨在高性能地实现模型和优化过程。该项目中的研究人员在光电子器件建模和制造方面具有良好的记录，他们之间的协同作用可以导致开发出具有卓越性能特性的器件。该计划中开发的设备将对运行在400 HZ(每个通道)及更高频率的下一代光波系统有用。

This research program is a theoretical and experimental interdisciplinary effort that will lead to the design of a new generation of ultrafast and high-accuracy photodetectors. The program will focus on the widely-used class of photodetectors known as thin avalanche photodiodes (APDs). This program is motivated by the need to meet the increasing demand for bandwidth in next-generation optical core networks, where there is a need to develop a new generation of low-noise and high responsivity photodetectors with gain-bandwidth products that are far beyond the current state-of-the-art. Moreover, since the capability of a lightwave network is ultimately limited by its architecture and the performance of its components, a thorough understanding of the fundamental performance limits of applicable photodetectors significantly impacts the design of future communication networks. In addition, with the emerging int~rest in using wide-bandgap-material technology in various high- accuracy and ultrafast sensing applications, there is a need for the development of high-performance photodetectors using wide-bandgap materials such as CaN.The first goal of this project is to develop and validate a rigorous renewal-theory-based model for the joint statistics of the gain and the response time of APDs. The model will be applicable to APDS with various structures and materials with special emphasis on thin APDs, which exhibit low multiplication noise and high bandwidth. The theory will specifically capture the important effect of dead space, which plays a principal role in the performance of thin APDs and significantly affects the performance of both ultrafast (intersymbol-interference limited) and lot-power (gain-fluctuation limited) applications. Significant improvements in the noise and bandwidth characteristics is to be achieved by reducing the thickness of the APD's multiplication layer, which is responsible for the device gain. To date, the fundamental limits of the statistics of the gain-bandwidth product for thin APDs, and more notably, the effect of reducing the thickness of the multiplication layer on the fluctuations in the response time remain unknown. These questions will be thoroughly addressed in this research and the fundamental limits of APD performance will be established.The second goal of this project is to utilize the developed model to design and develop next- generation high-performance APD's. Device fabrication and characterization will be carried out at the existing facilities at the Microelectronics Research Center at the University of Texas in Austin. The role played by the thickness of the avalanche multiplication layer of the device will be thoroughly investigated in an effort to design devices with application-specific optimal charac-teristics. Low-noise devices with gain-bandwidth products well beyond 500 CHz (bandwidths of 50-100 GHz) are to be developed in this program. Optimization criteria will include a) maximizing the data transmission rate subject to a fixed bit-error rate, which is applicable to intersymbol-interference-limited communication systems, and B) maximizing the receiver signal-to-noise ratio in power-limited sensing applications. As a tool in accomplishing the above objectives, a CAD tool will be designed consisting of custom-made parallel-computing algorithms intended for the high-performance implementation of the model and the optimization process.The synergy between the investigators in this project, who have a demonstrated record in opto-electronic device modeling and fabrication, can lead to the development of devices with superb per-formance characteristics. The devices developed in this program will be useful for next-generation lightwave systems operating at 40 0Hz (per channel) and beyond.