Plugging the 1 eV band gap gap: GaAsBiN as a highly mismatched alloy for multi-junction photovoltaics.

在这个项目中，将研究砷化镓的生长物理，最终证明这种材料在高效光伏发电方面的潜力。研究人员正在努力实现太阳能电池的效率超过50%，越来越深奥的设备设计被提出，以突破效率极限。成熟的多结装置设计（在不同的子电池中收集太阳光谱的不同区域）的理论效率限制远远超过50%。然而，目前的世界纪录效率只有46%。缺乏高质量的亚电池材料阻碍了这些设备的发展。一种好的候选材料将吸收适当的太阳光谱区域，并结合到现有的多结设计中，而不会在结构中造成应变，从而降低太阳能电池的性能。本研究提出的合金砷化铋氮化镓（GaAsBiN）是一种理想的候选材料。Bi和N对GaAs电子结构的巨大影响使得该合金的光学吸收谱易于定制；铋原子的大尺寸平衡了N原子的小尺寸，也允许合金被纳入现有的器件设计应变。然而，迄今为止，合成砷化镓的技术挑战限制了其发展。As， Bi和N之间的尺寸差异使得GaAsBiN晶体生长存在问题，需要非标准的生长条件和技术。世界上很少有实验室报道过GaAsBiN的生长，只有一个实验室展示了由这种材料组成的设备。该项目将分三个工作包完成：该项目的第一个工作包将涉及旨在生产简单GaAsN、GaAsBi和GaAsBiN测试样品的初步生长研究。从先前公布的生长参数开始，材料质量将通过生长条件调查进行优化。在第二个工作包中，工作包一中导出的生长参数将用于生产几个GaAsBiN器件，这些器件将使用标准电子技术进行表征。同时，选定的生长参数将用于生长薄的GaAsBiN层，这些层将在谢菲尔德大学用原子分辨率成像，并将在哈德斯菲尔德大学用原子层分辨率测量它们的Bi剖面。通过仔细分析表面图像和Bi轮廓，并将这些结果与相应的电子器件性能进行比较，将确定生长条件对材料成分和质量的影响。工作包三将利用在WP2中开发的生长条件来生产一系列GaAsBiN器件，这些器件将被表征以确定其光电性能和多结太阳能电池的适用性。

In this project, the growth physics of GaAsBiN will be investigated, culminating in a demonstration of the potential of this material for high efficiency photovoltaics.Researchers are striving to achieve solar cell efficiencies over 50 %, with ever more esoteric device designs being proposed to push efficiency limits. The well-established multi-junction device design (which harvests different regions of the solar spectrum in different sub-cells) has a theoretical efficiency limit well in excess of 50 %. However, the current world record efficiency is only 46 %. A lack of high quality sub-cell materials is hindering the development of these devices. A good candidate material will absorb an appropriate region of the solar spectrum and incorporate into existing multi-junction designs without causing strain in the structure, which degrades solar cell performance.The alloy proposed in this research, gallium arsenide bismide nitride (GaAsBiN), is an ideal candidate material. The dramatic impacts of Bi and N on the GaAs electronic structure allow the optical absorption profile of the alloy to be easily tailored; the large size of the Bi atom balancing the small size of the N atom also allows the alloy to be incorporated into existing device designs strain-free. However, the technical challenge of synthesising GaAsBiN has limited its development to date. The size differences between As, Bi and N make GaAsBiN crystal growth problematic, necessitating non-standard growth conditions and techniques. Very few laboratories around the world have reported GaAsBiN growth and only one has demonstrated a device comprising this material.The project will be completed in three work packages:The first work package of this project will involve preliminary growth studies aimed at producing simple GaAsN, GaAsBi, and GaAsBiN test samples. Starting with previously published growth parameters, the material quality will be optimised through a growth condition investigation.In the second work package, the growth parameters derived in work package one will be used to produce several GaAsBiN devices, which will be characterised using standard electronic techniques. In parallel, selected growth parameters will be used to grow thin GaAsBiN layers, which will be imaged with atomic resolution at the University of Sheffield and will have their Bi profiles measured with atomic layer resolution at the University of Huddersfield. Through careful analysis of the surface images and Bi profiles, and comparison of these results with the corresponding electronic device performances, the impact of growth conditions on material composition and quality will be determined.Work package three will use the growth condition understanding developed in WP2 to produce a series of GaAsBiN devices, which will be characterised to determine their opto-electronic performance and applicability for multi-junction solar cells.