Identification of point defects in GaN materials and their impact on device performance

该项目提议将曼彻斯特集团用于较小禁带材料的电学表征技术扩展数十年，以测量宽带隙半导体中缺陷的电学性质。目前最重要的宽禁带材料是GaN和InGaN。它们被用来制造低能耗LED照明和大功率晶体管。从材料的性质来看，今天这一代设备的功能并不像看起来可能的那样好，目前的功能和性能是有限的。这至少部分是由于组件材料和器件中存在点缺陷。例如，在LED中，由于带隙状态导致的肖克利-里德-霍尔复合仍然是一种显著的效率损失机制。学生将使用深能级瞬变光谱和光致发光技术来识别这些材料中点缺陷的性质，以及它们对实际LED和晶体管设备的影响。特定的缺陷和杂质将被引入，要么由工业合作者在生长过程中引入，要么通过例如注入或照射。然后，将使用所描述的技术来表征由此产生的缺陷能级，并评估器件性能的影响。氮化物材料作为半导体仍处于初级阶段，它们含有高水平的点缺陷、空位、间隙和杂质，如碳。这些缺陷的电子行为几乎完全未知。已知的是，现实世界中的设备显示出不受欢迎的特性，例如晶体管中的电流崩溃和LED中的异常效率下降。这些影响被认为是由于缺陷状态造成的，但到今天为止，还没有明确的证据表明是什么缺陷造成的。这个项目代表着在这一领域进行世界级、高影响力研究的巨大机会。

The project proposes to extend the electrical characterisation techniques used for smaller gap materials by the Manchester group for decades to measure the electrical properties of defects in wide band gap semiconductors. The most important wide gap materials at the present time are GaN and InGaN. They are used to make low energy LED lighting and highpower transistors. Today's generation of these devices does not function as well as would seem possible from the properties of the materials and at the present time functionality and performance is limited. This is due, at least in part, to the presence of point defects in the component materials and devices. Eg, In LEDs so called Shockley-Reed-Hall recombination due to gap states is still a significant efficiency loss mechanism. The student will use deep level transient spectroscopy and photoluminescence techniques to identify the nature of the point defects in these materials and how they impact on real LED and transistor devices. Particular defects and impurities will be introduced, either by the industrial collaborator during growth or by using eg implantation or irradiation. The resulting defect energy levels will be then characterised using the techniques described, and the impact of device performance assessed. The nitride materials are still their infancy as semiconductors, they contain high levels of point defects, vacancies, interstitials and impurities such as carbon. The electronic behaviour of these defects is almost completely unknown. What is known is that real world devices show undesirable properties such as current collapse in transistors and anomalous efficiency droop in LEDs. These effects are believed to be due to defect states, but as of today there is no definitive demonstration of what defect is responsible. This project represents a tremendous opportunity to perform world class, high impact, research in this area.