Defect reduction in GaN using the in-situ growth of transition metal nitride layers

基于GaAs和相关材料的红色、黄色和绿色LED自20世纪60年代以来就已经可用。然而，适用于蓝光LED的宽带隙半导体很难开发，直到1993年才制造出第一个高效，长寿命的蓝色GaN基LED。这彻底改变了固态照明领域，并启动了专注于GaN和相关材料的大量研究工作。然而，很快就发现GaN薄膜中的高密度穿透位错严重限制了GaN基器件在紫色和UV区域发射的性能。因此，许多研究工作都集中在位错密度降低上，以努力开发高效的紫色和UV发射LED和激光器。这些发射器本身对于水消毒、数据存储和通信是有用的，但是对于白色LED也是需要的，所述白色LED通常基于紫色或UV LED与磷光体的组合，所述磷光体将短波长光转换成红色、绿色和蓝色波长的适当混合物。如果白色LED的性能可以通过减少缺陷来改善，那么将产生具有比传统技术好得多的发光效率和寿命的固态照明。鉴于欧盟最近宣布禁止销售传统灯泡，这一举措尤为重要。我们相信，明亮的白色LED为英国的照明提供了最佳解决方案;荧光节能灯泡含有汞等有害金属（造成废物处理问题），体积大，而且往往显色性差。因此，我们提出的简短项目的目的是减少或消除（a）六方GaN（特别适合于LED的GaN形式）中的穿透位错和（B）立方GaN（特别适合于激光器的GaN形式）中的堆垛层错。这一雄心勃勃的目标是由我们的初步研究提出的，该研究表明，新型过渡金属氮化物夹层能够阻止这种位错传播到器件的有源发光区。我们打算通过使用用于生长GaN的相同技术（即用于六方GaN的MOCVD或用于立方GaN的MBE）在单个生长工艺中原位生长这样的层来开发这个概念。预期这将提供实际益处（不中断生长过程，如先前所要求的）和通过改善层的粗糙度来提供位错密度降低的显著改善，以及其他因素。然而，我们还打算这项工作为过渡金属氮化物与GaN器件的集成铺平道路，这可以改善LED接触技术，改善缓冲层技术，并允许制造高结构质量的超导TM-氮化物/绝缘GaN异质结构（约瑟夫森结），从而导致诸如用于医疗保健和生物物理学的超灵敏磁力计等应用。

Red, yellow and green LEDs based on GaAs and related materials have been available since the 1960s. However, wide band gap semiconductors suitable for blue LEDs were difficult to develop and the first efficient, long-lifetime blue GaN-based LED was not fabricated until 1993. This revolutionised the field of solid-state lighting and kick-started a considerable research effort focusing on GaN and related materials. However, it soon became clear that high densities of threading dislocations in the GaN films were severely limiting the performance of GaN-based devices that emit in the violet and UV region. Much research effort has therefore been focused on dislocation density reduction, in an effort to develop efficient violet and UV-emitting LEDs and lasers. These emitters are useful in their own right for water sterilisation, data storage and communications, but are also needed for white LEDs, which are commonly based on the combination of a violet or UV LED and phosphors which convert the short-wavelength light into an appropriate mixture of red, green and blue wavelengths. If the performance of white LEDs can be improved via defect reduction, then solid-state lighting with a luminous efficacy and lifetime considerably better than conventional technology will result. Such an initiative is particularly important in light of a recent EU announcement regarding the banning of sale of conventional light bulbs. We believe that bright, white LEDs offer the best solution for lighting the UK; fluorescent energy-saving bulbs contain harmful metals such as mercury (creating a waste disposal problem), are large in size and often provide poor colour rendering. The aim of our short proposed project is therefore to reduce or eliminate (a) threading dislocations in hexagonal GaN (a form of GaN particularly suitable for LEDs) and (b) stacking faults in cubic GaN (a form of GaN particularly suitable for lasers). This ambitious aim is prompted by our initial research, which indicated that novel transition metal nitride interlayers have the ability to block such dislocations from propagating into the active light-emitting region of a device. We intend to develop this concept by growing such layers in-situ in a single growth process using the same technique that is used to grow the GaN, namely MOCVD for hexagonal GaN or MBE for cubic GaN. This is expected to provide both practical benefits (no interruption of the growth process, as was previously required) and to provide significant improvements in dislocation density reduction via improvement in the roughness of the layers, among other factors. However, we also intend this work to pave the way for integration of transition metal nitrides with GaN devices, which could improve LED contact technology, improve buffer layer technology and allow superconducting TM-nitride/insulating GaN heterostructures (Josephson junctions) of high structural quality to be fabricated, leading to application such as ultra-sensitive magnetometers for use in healthcare and geophysics.