EAPSI:Investigation of Radiation Tolerance of Novel Semiconductor Materials for Space Power

光伏（PV）是空间探索的一项使能技术，在设计整个系统之前，需要对所采用技术的生命周期进行充分的描述和了解。中地球轨道（MEO）或轨道半径为地球半径（Re）的1.8至2.5倍的卫星寿命的一个主要问题是通过范艾伦带时的高能辐射效应，在范艾伦带中，带电粒子被地球磁场捕获。由于光伏系统暴露在辐射下会退化，因此卫星或航天器的总功耗受到光伏系统在使用寿命结束时所能提供的电量的限制。该项目的潜在目标是了解和设计在高辐射影响下表现出更好电气特性的材料，这是空间光伏社区非常感兴趣的话题。这项研究将在半导体材料辐射效应领域的专家Shin-Ichiro Sato博士的协助下，在日本原子能机构的半导体分析和辐射效应小组完成。该设施拥有最先进的太阳能电池辐照和测试设施，能够在相对较短的时间内完成广泛的研究。本项目将培养三套应变平衡量子点/量子阱太阳能电池（QDSC/QWSC）和量子点/量子阱（QD/QW）测试结构。第一组将针对紧张中性条件。第二组将被设计为具有轻微的压缩应变（通过x射线衍射仪验证~ 1000ppm），通过稀释GaP应变补偿层。最后，第三组将具有更厚的GaP应变补偿层，从而产生微拉伸（~1000 ppm）应变QD堆栈。位移冲击能的变化可以通过DLTS缺陷密度的变化来测量，如果量子点堆栈保持薄，相对较小的残余应变变化应该不会对电性能产生不利影响。由于量子点太阳能电池也将包括在内，因此有可能将这些变化与设备电性能的变化联系起来。这种器件阵列使得从固有量子点特性中提取残余应变的反卷积效应成为可能，从而增强了对添加纳米结构对材料辐射耐受性影响的理解。该研究将在InGaAs/GaAs量子阱中重复，以研究3D量子约束与1D量子约束对抑制太阳能电池辐射效应的影响。NSF EAPSI奖是与日本科学促进会合作资助的。

Photovoltaics (PV) is an enabling technology for space exploration, and the lifecycle of the technology employed needs to be well characterized and well understood before the full system can be designed. A major concern for the longevity of satellites in Medium Earth orbit (MEO), or orbital radii from 1.8 to 2.5 times the Earth's radius(Re) is the high energy radiation effects from passing through the Van Allen belts where charge particles are trapped by the Earth's magnetic field. Since the PV system degrades from exposure to radiation, the total power consumption of the satellite or vessel is limited by what the PV system can provide at end-of-life. The underlying goal of this project is to understand and engineer materials that exhibit better electrical characteristics under high radiation fluences, a topic of great interest to the space PV community. This research will be completed at the Semiconductor Analysis & Radiation Effects group of the Japan Atomic Energy Agency with the assistance of Dr. Shin-Ichiro Sato, an expert in the field of radiation effects in semiconductor materials. This facility possesses state-of-the-art solar cell irradiation and testing facilities, enabling completion of an extensive study in a relatively short period of time. For this project, three sets of strain balanced quantum dot/quantum well solar cells (QDSC/QWSC) and quantum dot/quantum well (QD/QW) test structures will be grown. The first set will target a strain-neutral condition. The second set will be designed to have a slightly compressive strain (~1000 parts per million (ppm) verified via x-ray diffractometry) by thinning the GaP strain compensation layer. Finally, the third set will have a thicker GaP strain compensation layer, resulting in a slightly tensile (~1000 ppm) strained QD stack. A change in required displacement knock-on energy should be measurable via changes in defect density from DLTS, and if the QD stack is kept thin, relatively minor changes in residual strain should not have detrimental effects on electrical properties. Since QD solar cells will also be included, it will be possible to correlate these changes to changes in electrical properties of devices. This array of devices makes it possible to deconvolve effects of residual strain from inherent QD properties in order to enhance understanding of the effects adding nanostructures has on radiation tolerance of the material. The study will be repeated with InGaAs/GaAs QWs in order to investigate the impact of 3D quantum confinement vs 1D quantum confinement on suppressing radiation effects in solar cells. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.