Investigations about the epitaxy of AlBGaN hetero structures for applications in UV-LEDs

在成功地优化了GaN基LED的可见光发射后，其他光谱范围越来越成为科学的焦点。在这个项目中，我们打算集中在短波长紫外线(UV-C)光谱范围内的LED，因为许多应用，如空气和水的杀菌和消毒变得越来越有趣。这类LED需要在AlN(准)衬底上生长AlGaN异质结构。这种异质结构中的一个主要问题仍然是相当高的缺陷密度，部分原因是不同单层之间的大晶格失配和所产生的应变。因此，我们打算研究如何通过使用硼(B)作为进一步的组份来处理这些问题。已经相当小的几个百分比的B分数可以帮助显著减少晶格失配。然而，B在AlGaN中的掺入是有限的，因为它的溶解度相当小。我们将采用温度高达1400°C的高温外延生长，以获得最佳的溶解度。我们的研究将澄清这是否确实有助于降低含铝异质结构中的应变-特别是在那些铝含量较大的异质结构中-而不会恶化晶体质量和缺陷密度。此外，目前关于这种四元材料体系的许多基本性质的信息很少，甚至是相互矛盾的，例如带隙随组成、带偏移、施主和受主电离能的函数而变化。通过在我们的样品上使用各种表征工具的相关方法进行测量，我们将找到这些问题的答案。由于六方氮化硼在掺镁方面具有很好的性能，我们还将进一步研究，这是否也能带来更好的AlBGaN层的p掺杂。

After having optimized successfully GaN-based LEDs for visible light emission, other spectral ranges move more and more into the scientific focus. In this project, we intend to concentrate on LEDs for the short wavelength ultraviolet (UV-C) spectral range, as many applications like sterilisation and disinfection of air and water become more and more interesting. Such LEDs require AlGaN hetero-structures grown on AlN (quasi) substrates. A major problem in such hetero-structures still is the fairly high defect density, partly caused by the large lattice mismatch between the different single layers and the resulting strain. Therefore, we intend to study how these problems can be managed by using boron (B) as a further component. Already quite small B fractions of a few percent can help reducing the lattice mismatch considerably. However, the incorporation of B into AlGaN is known to be limited because of a fairly small solubility. We will apply high-temperature epitaxial growth with temperatures up to 1400°C to get best solubility. Our investigations will clarify whether this indeed helps to reduce the strain in Al-containing hetero-structures - particularly in those with large Al content - without deteriorating the crystalline quality and defect density. Moreover, only scarce or even contradictory information about many fundamental properties of this quaternary material system such as band gap as function of composition, band offsets, donor and acceptor ionisation energies is currently available. By performing measurements with well-correlated methodology of various characterisation tools on our samples, we will find answers to such questions. Motivated by the very promising properties of hexagonal BN concerning p-doping with Mg, we will additionally investigate, whether this also can lead to better p-doping of AlBGaN layers.