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

该项目提议扩展曼彻斯特小组几十年来用于测量宽带隙半导体缺陷电性能的小间隙材料的电特性技术。目前最重要的宽隙材料是GaN和InGaN。它们被用于制造低能耗LED照明和高功率晶体管。从材料的特性来看，当今一代的这些设备的功能并不像看起来那样好，而且目前的功能和性能是有限的。这至少部分是由于元件材料和器件中存在点缺陷。在led中，由于间隙态而引起的肖克利-里德-霍尔复合仍然是一个重要的效率损失机制。学生将使用深层瞬态光谱和光致发光技术来识别这些材料中点缺陷的性质，以及它们如何影响真正的LED和晶体管器件。特定的缺陷和杂质将被引入，要么是由工业合作者在生长过程中，要么是通过植入或辐照。由此产生的缺陷能级将使用所描述的技术进行表征，并评估器件性能的影响。氮化材料作为半导体仍处于起步阶段，它们含有高水平的点缺陷、空位、间隙和碳等杂质。这些缺陷的电子行为几乎是完全未知的。我们所知道的是，现实世界的设备显示出不希望看到的特性，比如晶体管的电流崩溃和led的异常效率下降。这些影响被认为是由于缺陷状态造成的，但是到目前为止，还没有明确的证明是什么缺陷造成的。这个项目代表了在这个领域进行世界级、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.