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

该研究计划是一项理论和实验跨学科的努力，将导致新一代超快和高精度光电探测器的设计。该计划将重点关注广泛使用的一类光电探测器，称为薄雪崩光电二极管（APD）。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，需要开发新一代低噪声和高响应度的光电探测器，其增益带宽产品远远超过当前最先进的水平。此外，由于光波网络的能力最终受到其架构和组件性能的限制，对可应用的光电探测器的基本性能限制的透彻理解显著地影响未来通信网络的设计。此外，随着在各种高精度和超快传感应用中使用宽带隙材料技术的兴起，需要开发使用诸如CaN的宽带隙材料的高性能光电探测器。本项目的第一个目标是开发和验证用于APD的增益和响应时间的联合统计的严格的基于更新理论的模型。该模型将适用于各种结构和材料的APD，特别是薄APD，表现出低的乘法噪声和高带宽。该理论将具体捕捉死区的重要影响，它在薄APD的性能中起着主要作用，并显着影响超快（符号间干扰限制）和大功率（增益波动限制）应用的性能。噪声和带宽特性的显著改善将通过减小APD的倍增层的厚度来实现，该倍增层负责器件增益。到目前为止，薄APD的增益带宽积的统计的基本限制，更值得注意的是，在响应时间的波动上的倍增层的厚度减少的效果仍然未知。这些问题将在本研究中得到彻底解决，APD性能的基本限制将建立。本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APD。器件制造和表征将在奥斯汀德克萨斯大学微电子研究中心的现有设施中进行。器件雪崩倍增层的厚度所起的作用将被彻底研究，以设计出具有特定应用的最佳特性的器件。增益带宽产品远远超过500 CHz（50-100 GHz的带宽）的低噪声器件将在该计划中开发。优化标准将包括a）最大化受制于固定误码率的数据传输速率，这适用于码间干扰受限的通信系统，以及B）最大化功率受限感测应用中的接收机信噪比。作为实现上述目标的工具，将设计一个CAD工具，该工具由定制的并行计算算法组成，用于模型和优化过程的高性能实现。该项目中的研究人员在光电器件建模和制造方面有着良好的记录，他们之间的协同作用可以导致器件具有卓越的性能特性的开发。在这个计划中开发的设备将是有用的下一代光波系统工作在40 0 Hz（每通道）和超越。

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.