MSc Compound Semiconductor Electronics (PhD Progression 1+3)

卡迪夫的团队成功地在(111)硅(Si)衬底上生长了外延氮化镓(GaN)层。这可能是能够将用于光子学的发光二极管(LED)集成到标准硅工艺技术生产线上的一种解决方案。关键问题是GaN的-17%拉伸应变导致晶片开裂，以及由于GaN和Si之间的失配和热膨胀失配而产生密集的失配位错网络，以及为器件操作形成良好的欧姆电接触。在这项结合了电子显微镜和电子能谱的研究中，将探索和减少晶格应变的各种方法，其中一个关键问题是电触点的退火是否以及在多大程度上增强了GaN层中的应变弛豫。在项目A中，将使用常规的电子衍射对比度(EDC)、高分辨率晶格成像(HREM)和环形暗场(ADF)扫描透射电子显微镜(STEM)来成像位错线并在平面(自上而下)几何形状中测量位错线的密度，并在横截面几何中确定位错类型和位错核的图像。

The team in Cardiff successful grows epitaxial gallium nitride (GaN) layers on (111) silicon (Si) substrates. This may be one solution to enable integration of light emitting diodes (LEDs) for photonics onto standard Si process technology production lines. Key issues are wafer cracking due to -17% tensile strain of the GaN and the generation of dense misfit dislocation networks due to the misfit and the thermal expansion mismatch between GaN and Si and also the formation of good ohmic electrical contacts for device operation. Various methods to explore and reduce lattice strain will be investigated in this combined electron microscopy and electron spectroscopy study where one key question to answer is whether and to what degree the anneal of the electrical contacts enhances strain relaxation in the GaN layers underneath.Conventional electron diffraction contrast (EDC), high-resolution lattice imaging (HREM), and annular dark-field (ADF) scanning transmission electron microscopy (STEM) will be used in project A to image dislocation lines and measure their density in plan-view (top-down) geometry, and to determine the dislocation types and image their cores in cross-sectional geometry.