Excellence in Research: GaAsSb/GaAs Nanowires based Avalanche Photodetectors on Si

单光子探测装置是量子信息电路的重要组成部分。纳米线结构的雪崩光电探测器是实现单光子探测的一种很有前途的途径，因为它可以减少冲击电离区域，从而提高增益和探测率。此外，纳米线结构中晶格失配约束的放松使雪崩光电探测器能够集成到传统的硅技术中。在1.3 ~ 1.55微米的光通信波长范围内，GaAsSb是一种理想的波长可调材料体系。GaAsSb/GaAs异质结构将被设计为独立的倍增区和吸收区，前者发生在较大带隙的GaAs结中，以最小化齐纳击穿的影响，这是低带隙材料中常见的问题。本提案的中心主题是在硅基GaAsSb/GaAs纳米线雪崩光电探测器异质结构中独立光吸收和倍增区的生长和设计优化。两种不同的纳米线结构，即轴向和核壳将使用各种材料和器件表征技术进行检查。实验工作将通过使用不同软件包进行建模来补充。重点将放在三维电场的增加工程上，并深入了解两种不同纳米线结构中的雪崩机制（载流子的倍增）。在最后阶段，将对这两种结构的性能进行评估，以达到优化设计，从而实现近红外区域增益超过10的纳米雪崩光电探测器。技术：雪崩光电探测器通常用于高速，高增益和低光信号检测应用。对基于纳米线的雪崩光电探测器的兴趣源于单光子探测装置的潜在成功。纳米线结构由于其一维属性导致了独特而新颖的材料特性，并同时使薄膜技术的制造工艺得以适应。晶格失配约束的放松，占地面积小，高表面体积比，优越的光捕获以及在不同纳米线架构中实现的可行性可以策略性地用于提高探测器性能并实现与传统Si技术的异质集成。在提出的工作中，从薄膜形式分离的光学吸收和倍增区雪崩光电探测器概念将以独特的方式适用于GaAsSb/GaAs异质结构的带隙工程，仅适用于纳米线结构。选择了GaAsSb材料体系，因为它包含了在电信波长区域可调谐的带隙。雪崩光电探测器的实现将实现不同的设计理念：轴向和径向结构，后者是纳米线配置所独有的。基于纳米线系综的雪崩光电探测器的研究能够利用垂直排列的优势，从而实现优越的光捕获特性，从而增强光吸收。在最后阶段，我们将对两种不同结构下的性能进行评估，以获得在近红外区域增益超过10的纳米雪崩光电探测器的优化设计。这项研究将深入了解光导调制对纳米线雪崩机制的影响，这是由于纳米线表面靠近NW核心而产生的带弯曲，特别是在轴向结构中。在异质结构设计方面取得的进展将在低维结构中实现更大的三维电场，这将使器件性能得到革命性的改善，对材料和器件的研究产生重大影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

An important building block of the quantum information circuit is the single photon detection device. The avalanche photodetector in the nanowire configuration is a promising route to achieving single photon detection as it enables reduction in the impact ionization region, thus improving gain and detectivity. Further, the relaxation of the lattice mismatch constraint in the nanowire configuration enables integration of the avalanche photodetector to the traditional silicon technology. GaAsSb is an ideal material system for wavelength tunability in the optical communication wavelength range of 1.3 - 1.55 microns. The GaAsSb/GaAs heterostructure will be designed for independent multiplication and absorption regions, with the former occurring in the larger bandgap GaAs junction to minimize the effect of Zener breakdown, which is a common problem in low band gap materials. This proposal's central theme is on the growth and design optimization of the separate optical absorption and multiplication region in the GaAsSb/GaAs nanowire based avalanche photodetector heterostructure on Si. Two different nanowire configurations namely axial and core-shell will be examined using a variety of material and device characterization techniques. The experimental work will be complemented by modeling using different software packages. Emphasis will be on engineering the increase of the electric field in 3D and gaining deeper insight into the avalanche mechanism (multiplication of the carriers) in the two different nanowire configurations. The performance in these two configurations will be evaluated to arrive at an optimized design in the final phase to achieve nano-avalanche photodetector with gain exceeding 10 in the near infrared region. Technical: Avalanche photodetectors are commonly used for high speed, high gain and low optical signal detection applications. The interest in nanowire - based avalanche photodetectors stems from the potential success of single photon detection devices. Nanowire architecture due to its one dimensional attributes leads to unique and novel material properties and concomitantly enables adaptation of fabrication processes from thin film technology. The relaxation of lattice mismatch constraint, small footprint, high surface to volume ratio, superior optical trapping and feasibility of implementing in different nanowire architectures can be strategically used to improve the detector performance and enabling heterogeneous integration with traditional Si technology. In the proposed work, separate optical absorption and multiplication region avalanche photodetector concepts from the thin film form will be adapted toward bandgap engineering of GaAsSb/GaAs heterostructure in a unique manner, exclusive to the nanowire architecture. The GaAsSb material system has been chosen as it encompasses the bandgap tunable in the telecommunication wavelength region. Different design concepts in the implementation of avalanche photodetector will be realized: axial and radial architectures, the latter of which is exclusive to the nanowire configuration. The investigation of nanowire ensemble based avalanche photodetectors enable taking advantage of the vertical alignment that allows superior light trapping properties leading to enhanced optical absorption. The performance in the two different configurations will be evaluated to arrive at an optimized design in the final phase to achieve nano-avalanche photodetector with gain exceeding 10 in the near infrared region. This study will provide deeper insight into the effect of photoconductivity modulation on the avalanche mechanism in nanowires due to the band bending at the surface stemming from the close proximity of the surface to the core of the NW, particularly in axial architecture. Advances made in the heterostructure design toward achieving an increased 3D electric field in a lower dimensional structure will enable transformational improvement in the device performance with significant impact on material and device research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.