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

光电技术是一种空间探索的赋能技术，在设计整个系统之前，需要对所采用的技术的生命周期进行充分的描述和了解。对于中地球轨道（MEO）或轨道半径为地球半径（Re）的1.8倍至2.5倍的卫星的寿命的主要关注是来自穿过货车艾伦带的高能辐射效应，在该带中，带电粒子被地球磁场捕获。由于光伏系统因暴露于辐射而退化，卫星或船舶的总功耗受到光伏系统在寿命结束时可以提供的功率的限制。该项目的基本目标是了解和设计在高辐射通量下表现出更好电气特性的材料，这是空间光伏界非常感兴趣的一个主题。这项研究将在日本原子能机构的半导体分析辐射效应小组中完成，并得到半导体材料辐射效应领域专家Shin-Ichiro Sato博士的协助。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。本项目将生长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。第一组将针对应变中性条件。第二组将被设计为通过减差距应变补偿层而具有轻微的压缩应变（通过X射线衍射法验证的约1000 ppm）。最后，第三组将具有较厚的GaP应变补偿层，导致轻微拉伸（~1000 ppm）应变的QD堆叠。所需的位移撞击能量的变化应当是经由来自DLTS的缺陷密度的变化可测量的，并且如果QD堆叠保持薄，则残余应变的相对较小的变化不应当对电性质具有有害影响。由于量子点太阳能电池也将被包括在内，因此将有可能将这些变化与设备的电气特性变化相关联。这种器件阵列使得可以从固有的QD特性中去卷积残余应变的影响，以增强对添加纳米结构对材料的辐射耐受性的影响的理解。该研究将重复与InGaAs/GaAs量子阱，以研究3D量子限制与1D量子限制对抑制太阳能电池中的辐射效应的影响。这个NSF EAPSI奖是与日本科学促进协会合作资助的。

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.